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Home My WebLink AboutSWMM Volume 4 thur 6 Volume IV i Table of Contents Volume IV – Source Control Best Management Practices Table of Contents Purpose of this Volume ........................................................................... ........................................457 Content and Organization of this Volume .......................................................................................457 Chapter 1 Frequently Asked Questions ...........................................................................458 1.1 Applicability.......................................................................... .................................................458 1.2 Pollutants of Concern ............................................................................................................458 1.2.1 pH................................................................................................................................... 458 1.2.2 Total Suspended Solids .......................... ........................................................................ 458 1.2.3 Oils and Greases ................................................................................................... ......... 458 1.2.4 Oxygen-demanding Substances..................................................................................... 458 1.2.5 Metals.................................................. ........................................................................... 459 1.2.6 Bacteria and Viruses ............................................................................................ ........... 459 1.2.7 Nutrients......................................................................................................................... 459 1.2.8 Toxic Organic Compounds ............................................................................................. 459 1.2.9 Other Chemicals and Substances ................................................................ .................. 459 1.3 Types of Source Control BMPs .............................................................................................460 1.3.1 Operational BMPs ....................... .................................................................................... 460 1.3.2 Structural BMPs ........................................................................................ ...................... 460 Chapter 2 Worksheet for Commercial and Industrial Activities .....................................461 Chapter 3 BMPs for Homeowners ........................................ ............................................465 3.1 Automobile Washing (for Single-Family Residences) ...........................................................465 3.1.1 Suggested BMPs ............................................................................................................ 465 3.1.1.1 At Home ...................................................................... ..........................................465 3.1.1.2 Away from Home...................................................................................................466 3.2 Automobile Maintenance .......................................................................................................466 3.2.1 Required BMPs ............................................................ ................................................... 466 3.2.2 Suggested BMPs ............................................................................................................ 466 3.3 Storage of Solid Wastes and Food Wastes...........................................................................467 3.3.1 Suggested BMPs .................................................... ........................................................ 467 Volume IV ii Table of Contents 3.4 Composting...........................................................................................................................467 3.4.1 Suggested BMPs ............................................................................................................ 467 3.5 Yard Maintenance and Gardening .............................................. ..........................................468 3.5.1 Required BMPs ............................................................................................................... 468 3.5.2 Suggested BMPs ............................................................................................................ 468 3.6 Swimming Pool and Spa Cleaning and Maintenance ...........................................................469 3.6.1 Required BMPs ............................................................................................................... 469 3.6.2 Suggested BMPs ............................................................................................................ 469 3.7 Household Hazardous Material Use, Storage, and Disposal ................................................469 3.7.1 Required BMPs ............................................................................................................... 470 3.7.2 Suggested BMPs ............................................................................................................ 470 3.8 General Home Maintenance................................. .................................................................471 3.8.1 Suggested BMPs ............................................................................................................ 471 3.9 Pet Waste ..............................................................................................................................471 3.9.1 Suggested BMPs .............................. .............................................................................. 471 Chapter 4 BMPs for Commercial and Industrial Activities..............................................472 4.1 BMPs to Consider for all Activities ........................................................................................472 4.2 Cleaning and Washing Activities ............................... ............................................................473 4.2.1 BMP A101: Cleaning or Washing of Tools, Engines and Manufacturing Equipment .... 473 4.2.1.1 Description of Pollutant Sources ...........................................................................473 4.2.1.2 Pollutant Control Approach ............................................................................. ......473 4.2.1.3 Required BMPs .....................................................................................................473 4.2.1.4 Recommended BMPs ..................................... ......................................................474 4.2.2 BMP A102: Cleaning or Washing of Cooking Equipment............................................... 476 4.2.2.1 Description of Pollutant Sources ...........................................................................476 4.2.2.2 Pollutant Control Approach ................................................................ ...................476 4.2.2.3 Required BMPs .....................................................................................................476 4.2.2.4 Recommended BMPs ........................ ...................................................................477 4.2.3 BMP A103: Washing, Pressure Washing and Steam Cleaning of Vehicles/Equipment/Building Structures ......................... ............................................................. 478 4.2.3.1 Description of Pollutant Sources ...........................................................................478 4.2.3.2 Pollutant Control Approach ...................................................................................478 4.2.3.3 Required BMPs: ...................................................... ..............................................478 4.2.3.4 General..................................................................................................................480 4.2.4 BMP A104: Collection and Disposal of Wastewater in Mobile Interior Washing Operations............................................................................................................ .......... 481 4.2.4.1 Description of Pollutant Sources ...........................................................................481 4.2.4.2 Pollutant Control Approach ............................. ......................................................481 4.2.4.3 Required BMPs .....................................................................................................481 4.2.4.4 Recommended BMPs ...........................................................................................482 Volume IV iii Table of Contents 4.3 Transfer of Liquid or Solid Materials......................................................................................483 4.3.1 BMP A201: Loading and Unloading Areas for Liquid or Solid Material .......................... 483 4.3.1.1 Description of Pollutant Sources ...........................................................................483 4.3.1.2 Pollutant Control Approach ...................................................................................483 4.3.1.3 Required BMPs ....................................................... ..............................................483 4.3.1.4 Recommended BMPs: ..........................................................................................486 4.3.2 BMP A202: Fueling at Dedicated Stations...................................................................... 488 4.3.2.1 Description of Pollutant Sources ...................................................... .....................488 4.3.2.2 Pollutant Control Approach ...................................................................................488 4.3.2.3 Required BMPs: ............................. .......................................................................488 4.3.3 BMP A203: Vehicle Maintenance Activities .................................................................... 494 4.3.3.1 Description of Pollutant Sources ...........................................................................494 4.3.3.2 Pollutant Control Approach ........................................ ...........................................494 4.3.3.3 Required BMPs .....................................................................................................494 4.3.3.4 Recommended BMPs ...........................................................................................495 4.3.4 BMP A204: Mobile Fueling of Vehicles and Heavy Equipment ........................ .............. 496 4.3.4.1 Description of Pollutant Sources ...........................................................................496 4.3.4.2 Pollutant Control Approach ......................... ..........................................................496 4.3.4.3 Required BMPs .....................................................................................................496 4.4 Production and Application Activities ....................................................................................499 4.4.1 BMP A301: Concrete and Asphalt Mixing and Production at Stationary Sites............... 499 4.4.1.1 Description of Pollutant Sources ...........................................................................499 4.4.1.2 Pollutant Control Approach ...................................................................................499 4.4.1.3 Required BMPs ................................................................................. ....................499 4.4.1.4 Recommended BMPs ...........................................................................................500 4.4.2 BMP A302: Concrete Pouring, Concrete Cutting, and Asphalt Application at Temporary Sites.............................................................................................................. 501 4.4.2.1 Description of Pollutant Sources ...........................................................................501 4.4.2.2 Pollutant Control Approach ................................................................ ...................501 4.4.2.3 Required BMPs .....................................................................................................501 4.4.2.4 Recommended BMPs ........................ ...................................................................502 4.4.3 BMP A303: Manufacturing and Post-Processing of Metal Products .............................. 503 4.4.3.1 Description of Pollutant Sources ...........................................................................503 4.4.3.2 Pollutant Control Approach .................................................... ...............................503 4.4.3.3 Required BMPs .....................................................................................................503 4.4.3.4 Recommended BMPs ...........................................................................................504 4.4.4 BMP A304: Wood Treatment Areas............................................................... ................. 505 4.4.4.1 Description of Pollutant Sources ...........................................................................505 4.4.4.2 Pollutant Control Approach ...................... .............................................................505 4.4.4.3 Required BMPs .....................................................................................................505 4.4.4.4 Recommended BMP .............................................................................................506 Volume IV iv Table of Contents 4.4.5 BMP A305: Commercial Composting ............................................................................. 507 4.4.5.1 Description of Pollutant Sources ...........................................................................507 4.4.5.2 NPDES Permit Requirements .............................................................................. .507 4.4.5.3 Pollutant Control Approach ...................................................................................507 4.4.5.4 Required BMPs .................................................. ...................................................507 4.4.5.5 Recommended BMPs ...........................................................................................508 4.4.6 BMP A306: Landscaping and Lawn/Vegetation Management ....................................... 509 4.4.6.1 Description of Pollutant Sources ................................................................. ..........509 4.4.6.2 Pollutant Control Approach ...................................................................................509 4.4.6.3 Required BMPs for Landscaping ......................... .................................................509 4.4.6.4 Recommended BMPs for Landscaping.................................................................509 4.4.6.5 Required BMPs for the Use of Pesticides .............................................................510 4.4.6.6 Recommended BMPs for the use of Pesticides....................................................511 4.4.6.7 Required BMPs for Vegetation Management .......................................................512 4.4.6.8 Fertilizer Management:.............................................................. ............................512 4.4.6.9 Integrated Pest Management ................................................................................513 4.4.7 BMP A307: Painting, Finishing and Coating of Vehicles, Boats, Buildings and Equipment ................................................................................................................................... 514 4.4.7.1 Description of Pollutant Sources ...........................................................................514 4.4.7.2 Pollutant Control Approach ........................................ ...........................................514 4.4.7.3 Required BMPs .....................................................................................................514 4.4.7.4 Recommended BMPs ...........................................................................................515 4.4.8 BMP A308: Commercial Printing Operations......................................... ......................... 516 4.4.8.1 Description of Pollutant Sources ...........................................................................516 4.4.8.2 Pollutant Control Approach ...................................................................................516 4.4.8.3 Required BMPs .......................................................................................... ...........516 4.4.8.4 Recommended BMPs ...........................................................................................516 4.4.9 BMP A309: Manufacturing Operations – Outside.............. ............................................. 517 4.4.9.1 Description of Pollutant Sources ...........................................................................517 4.4.9.2 Pollution Control Approach ...................................................................................517 4.4.9.3 Required BMPs ......................................................................... ............................517 4.5 Storage and Stockpiling Activities .........................................................................................519 4.5.1 BMP A401: Storage or Transfer (Outside) of Solid Raw Materials, By-Products or Finished Products ........................................................................................................................ 519 4.5.1.1 Description of Pollutant Sources ...........................................................................519 4.5.1.2 Pollutant Control Approach ........................................ ...........................................519 4.5.1.3 Required BMPs .....................................................................................................519 4.5.1.4 Recommended BMPs ...........................................................................................520 4.5.2 BMP A402: Storage and Treatment of Contaminated Soils ........................... ................ 522 4.5.2.1 Description of Pollutant Sources ...........................................................................522 4.5.2.2 Pollutant Control Approach ....................... ............................................................522 4.5.2.3 Required BMPs .....................................................................................................522 4.5.2.4 Recommended BMPs ...........................................................................................522 Volume IV v Table of Contents 4.5.3 BMP A403: Temporary Storage or Processing of Fruits or Vegetables ......................... 523 4.5.3.1 Description of Pollutant Sources .......................... .................................................523 4.5.3.2 Pollutant Control Approach ...................................................................................523 4.5.3.3 Required BMPs .....................................................................................................523 4.5.3.4 Recommended BMPs ....................................................... ....................................524 4.5.4 BMP A404: Storage of Solid Wastes and Food Wastes................................................. 525 4.5.4.1 Description of Pollutant Sources ...........................................................................525 4.5.4.2 Pollutant Control Approach ............................................................................. ......525 4.5.4.3 Required BMPs .....................................................................................................525 4.5.4.4 Recommended BMPs ..................................... ......................................................526 4.5.5 BMP A405: Recyclers and Scrap Yards ......................................................................... 527 4.5.5.1 Description of Pollutant Sources ...........................................................................527 4.5.5.2 Required BMPs ................................................................. ....................................527 4.5.6 BMP A406: Treatment, Storage or Disposal of Dangerous Wastes............................... 528 4.5.7 BMP A407: Storage of Liquid, Food Waste or Dangerous Waste Containers ............... 529 4.5.7.1 Description of Pollutant Sources ...........................................................................529 4.5.7.2 Pollutant Control Approach ...................................................................................529 4.5.7.3 Required BMPs ............................................................... ......................................529 4.5.8 BMP A408: Storage of Liquids in Above-Ground Tanks................................................. 532 4.5.8.1 Description of Pollutant Sources ...........................................................................532 4.5.8.2 Pollutant Control Approach ............................................................................. ......532 4.5.8.3 Required BMPs for All Tanks ................................................................................532 4.5.8.4 Required BMPs for Single-walled Tanks........................ .......................................533 4.5.8.5 Recommended BMPs for Double-walled Tanks ...................................................533 4.5.9 BMP A409: Parking and Storage for Vehicles and Equipment....................................... 535 4.5.9.1 Description of Pollutant Sources ...........................................................................535 4.5.9.2 Required BMPs .....................................................................................................535 4.6 Construction and Demolition Activities ............................. .....................................................536 4.6.1 BMP A501: Clearing, Grading and Preparation of Construction Sites ........................... 536 4.6.2 BMP A502: Demolition of Buildings ................................................................................ 537 4.6.2.1 Description of Pollutant Sources ............................................................ ...............537 4.6.2.2 Pollutant Control Approach ...................................................................................537 4.6.2.3 Required BMPs .................................... .................................................................537 4.6.2.4 Recommended BMPs ...........................................................................................537 4.6.3 BMP A503: Building, Repair, Remodeling and Construction.......................................... 538 4.6.3.1 Description of Pollutant Sources .................................................. .........................538 4.6.3.2 Pollutant Control Approach ...................................................................................538 4.6.3.3 Required BMPs .......................... ...........................................................................538 4.6.3.4 Recommended BMPs ...........................................................................................539 4.7 Dust Control, and Soil and Sediment Control........................................................................540 Volume IV vi Table of Contents 4.7.1 BMP A601: Dust Control at Disturbed Land Areas and Unpaved Roadways and Parking Lots ............................................................................. ....................................... 540 4.7.1.1 Description of Pollutant Sources ...........................................................................540 4.7.1.2 Pollutant Control Approach ...................................................................................540 4.7.1.3 Required BMPs ......................................................................... ............................540 4.7.1.4 Recommended BMPs for Roadways and Other Trafficked Areas:.......................540 4.7.1.5 Recommended BMPs for Dust Generating Areas: ....................... ........................541 4.7.2 BMP A602: Dust Control at Manufacturing Sites............................................................ 542 4.7.2.1 Description of Pollutant Sources ...........................................................................542 4.7.2.2 Pollutant Control Approach ...................................................................................54 2 4.7.2.3 Required BMPs .....................................................................................................542 4.7.2.4 Recommended BMPs ............................................. ..............................................542 4.7.3 BMP A603: Soil Erosion and Sediment Control at Industrial Sites................................. 543 4.7.3.1 Description of Pollutant Sources ...........................................................................543 4.7.3.2 Pollutant Control Approach ............................................................................. ......543 4.7.3.3 Required BMPs .....................................................................................................543 4.8 Other Activities.......................................... ............................................................................544 4.8.1 BMP A701: A701: Commercial Animal Handling Areas............................................................ 544 4.8.1.1 Description of Pollutant Sources ...........................................................................544 4.8.1.2 Pollutant Control Approach ........................................ ...........................................544 4.8.1.3 Required BMPs .....................................................................................................544 4.8.2 BMP A702: Log Sorting and Handling ............................................................................ 545 4.8.2.1 Description of Pollutant Sources .............................................. .............................545 4.8.2.2 Ecology’s Baseline General Permit Requirements ...............................................545 4.8.3 BMP A703: Boat Building, Maintenance and Repair ...................................................... 546 4.8.3.1 Description of Pollutant Sources ...........................................................................546 4.8.3.2 Pollutant Control Approach ...................................................................................546 4.8.3.3 Required BMPs ....................................................... ..............................................546 4.8.3.4 Recommended BMPs ...........................................................................................547 4.8.4 BMP A704: Logging ........................................................................................................ 549 4.8.4.1 Description of Pollutant Sources ......................................... ..................................549 4.8.4.2 Pollutant Control Approach ...................................................................................549 4.8.4.3 Required BMPs .....................................................................................................549 4.8.4.4 Recommended BMPs ..................................................................... ......................550 4.8.5 BMP A705: Mining and Quarrying of Sand, Gravel, Rock, Peat, Clay and Other Materials................................................................................... ............................. 551 4.8.5.1 Description of Pollutant Sources ...........................................................................551 4.8.5.2 Recommended BMPs .................... .......................................................................551 4.8.6 BMP A706: Swimming Pool and Spa Cleaning and Maintenance ................................. 552 4.8.6.1 Description of Pollutant Sources ...........................................................................552 4.8.6.2 Pollutant Control Approach .................................................... ...............................552 4.8.6.3 Required BMPs .....................................................................................................552 4.8.6.4 Recommended BMP .............................................................................................552 Volume IV vii Table of Contents 4.8.7 BMP A707: De-Icing and Anti-Icing Operations for Streets & Highways........................ 553 4.8.7.1 Description of Pollutant Sources ........................ ...................................................553 4.8.7.2 Required BMPs .....................................................................................................553 4.8.7.3 Recommended BMPs ...........................................................................................553 4.8.8 BMP A708: Roof and Building Drains at Manufacturing and Commercial Buildings...... 554 4.8.8.1 Description of Pollutant Sources ...........................................................................554 4.8.8.2 Pollutant Control Approach ...................................................................................554 4.8.8.3 Required BMPs .......................................................................................... ...........554 4.8.9 BMP A709: Urban Streets............................................................................................... 555 4.8.9.1 Description of Pollutant Sources ...........................................................................555 4.8.9.2 Pollutant Control Approach ...................................................................................55 5 4.8.9.3 Recommended BMPs ...........................................................................................555 4.8.10 BMP A710: Railroad Yards ............................................. ................................................ 557 4.8.10.1 Description of Pollutant Sources ...........................................................................557 4.8.10.2 Pollutant Control Approach ...................................................................................557 4.8.10.3 Required BMPs .............................................................. .......................................557 4.8.11 BMP A711: Maintenance of Public and Utility Corridors and Facilities .......................... 558 4.8.11.1 Description of Pollutant Sources ...........................................................................558 4.8.11.2 Pollutant Control Approach ............................................................................ .......558 4.8.11.3 Required BMPs .....................................................................................................558 4.8.11.4 Recommended BMPs .................................. .........................................................559 4.8.12 BMP A712: Maintenance of Roadside Ditches............................................................... 560 4.8.12.1 Description of Pollutant Sources ...........................................................................560 4.8.12.2 Pollutant Control Approach ................................................... ................................560 4.8.12.3 Required BMPs .....................................................................................................560 4.8.12.4 Recommended BMPs ...........................................................................................561 4.8.13 BMP A713: Maintenance of Stormwater Drainage and Treatment Facilities ................ 562 4.8.13.1 Description of Pollutant Sources ...........................................................................562 4.8.13.2 Pollutant Control Approach ...................................... .............................................562 4.8.13.3 Required BMPs .....................................................................................................562 4.8.14 BMP A714: Spills of Oil and Hazardous Substances ..................................................... 564 4.8.14.1 Description of Pollutant Sources .................................................. .........................564 4.8.14.2 Pollutant Control Approach ...................................................................................564 4.8.14.3 Required BMPs ........................ .............................................................................564 4.8.14.4 Recommended BMPs ...........................................................................................5 65 4.8.15 BMP A715: Water Reservoir, Transmission Mainline, Wellhead, and Hydrant Flushing Activities ................................................................................................. .......... 566 4.8.15.1 Description of Pollutant Sources ...........................................................................566 4.8.15.2 Pollutant Control Approach ........................... ........................................................566 4.8.15.3 Required BMPs .....................................................................................................566 4.8.15.4 Recommended BMPs ...........................................................................................566 4.8.16 BMP S101: Eliminate Illicit Storm Drainage System Connections ................................. 568 4.8.17 BMP S102: Dispose of Contaminated Stormwater and Waste Waste Materials Properly ........ 569 Volume IV viii Table of Contents 4.8.18 BMP S103: Discharge Process Wastewater to a Sanitary Sewer, Holding Tank, or Water Treatment System............................................................ ................................ 570 4.8.19 BMP S108: Implement Integrated Pest Management Measures ................................... 571 4.8.20 BMP S109: Cleaning Catch Basins .................... ............................................................ 572 4.9 Cover and Surround Activities ...............................................................................................573 4.9.1 BMP S104: Cover the Activity with a Roof or Awning..................................................... 573 4.9.2 BMP S105: Cover the Activity with an Anchored Tarp or Plastic Sheet ......................... 574 4.9.3 BMP S106: Pave the Activity Area and Slope to a Sump, Holding Tank, or Oil/Water Separator .................................................................. ...................................... 575 4.9.4 BMP S107: Surround the Activity Area with a Curb, Dike, or Berm or Elevate the Activity............................................................... ............................................................. 576 Chapter 5 Regulations and Requirements.......................................................................580 5.1 City of Auburn Codes and Ordinances..................................................................................580 5.2 State, Federal, and Other Regulations and Requirements ................... ................................580 5.2.1 Washington State Department of Ecology Requirements for the Discharge of Process Wastewaters Directly to Surface Waters ..................................... ..................... 580 5.2.2 Washington State Department of Ecology Requirements for Dangerous Waste Generators .................................................................................... ....................... 581 5.2.3 Washington State Department of Ecology Stormwater NPDES NPDES Permit Requirements.................................................................................... .............................. 581 5.2.4 Washington State Department of Ecology Requirements for Underground and Above Ground Storage Tanks ........................................................... ............................. 582 5.2.5 U.S. Environmental Protection Agency and Ecology Emergency Spill Cleanup Requirements.......................................................................... ........................................ 582 5.2.6 Washington State Department of Agriculture Pesticide Regulations.............................. 582 5.2.7 Puget Sound Clean Air Agency Air Quality Regulations................................................. 582 Appendix A Quick Reference Phone Numbers ...................................................................583 Appendix B Recycling/Disposal of Vehicle Fluids and Other Wastes...............................584 Appendix C Example of an Integrated Pest Management Program (IPM) .........................585 Appendix D Recommendations for Management of Street Wastes..................................588 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Purpose Volume IV Content and Organization 4 57 Introduction Volume IV: Source Control Best Management Practices Purpose of this Volume This volume was designed to help businesses, homeowners and public agencies in Auburn implement source control best management practices (BMPs) to prevent pollutants from contaminating stormwater runoff and entering our rivers, streams and groundwater. Content and Organization of this Volume Volume IV contains five chapters and four appendices. • Chapter 1 provides an overview of who should use this volume and the type of pollutants being targeted. • Chapter 2 provides a worksheet for commercial and industrial activity. • Chapter 3 provides BMPs for single-family residences. • Chapter 4 provides BMPs for commercial and industrial activities. • Chapter 5 lists related regulations and requirements. • Appendix A provides a list of phone numbers for related agencies. • Appendix B lists recommended management procedures for the handling of hazardous wastes. • Appendix C provides an example of an Integrated Pest Management program. • Appendix D provides recommendations for the management of street wastes. Volume IV S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Frequently Asked Questions Volume IV 4 58 Chapter 1 Chapter 1 Frequently Asked Questions 1.1 Applicability The implementation of BMPs applies to all businesses, residences, and public agencies in Auburn. 1.2 Pollutants of Concern The City is required to show progress in eliminating virtually all non-stormwater discharges to the storm drainage system. Only uncontaminated stormwater may be discharged to the City of Auburn storm drainage system. Illicit discharges, intentional or unintentional, are not allowed and polluters may be subject to state and federal penalties. It is the property owner’s responsibility to keep pollutants from leaving a property and entering the City storm drainage system. Pollutants can be placed into several broad categories, as listed below. 1.2.1 pH The pH value of a substance is a relative measure of whether it is acidic or basic. Most aquatic species can only survive in neutral conditions. Sources that can contribute to a change in pH of stormwater and waterbodies include cement in concrete pouring, paving, and recycling operations; solutions from metal plating; chemicals from printing businesses and other industrial processes; and household cleaners such as bleaches and deck washes. 1.2.2 Total Suspended Solids This represents particulate solids such as eroded soil, heavy metal precipitates, and biological solids which can cause sedimentation in streams and turbidity in receiving surface waters. Sediments can destroy the desired habitat for fish and can impact drinking water supplies. Sediment may be carried to streams, rivers and eventually to Puget Sound where they may be toxic to aquatic life and destroy habitat. 1.2.3 Oils and Greases Oils and greases can be either petroleum-based or food-related sources. Petroleum-based compounds can be immediately toxic to fish and wildlife, and can destroy our drinking water aquifers. Food-based oils and greases can coat fish gills and insects, suffocating them. Oils and greases can clog conveyance systems, which may cause flooding. 1.2.4 Oxygen-demanding Substances Degradable organic matter, such as yard, food, and pet wastes, and some chemical wastes, can have a drastic effect on water quality. These substances, when broken down by bacteria, consume the oxygen in the water. This stresses and can eventually kill fish and other creatures in the water. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Frequently Asked Questions Volume IV 4 59 Chapter 1 1.2.5 Metals Metals are utilized in many products important to our daily lives. Certain metals, known as heavy metals, wear off of our car brakes and tires, and come from the paint and moss-killing roof strips and herbicides we use at our homes. These metals can cause severe health and reproductive problems in fish and animals that live in water. Metals can be transported on sediments to waterbodies. 1.2.6 Bacteria and Viruses Bacteria and viruses from pet wastes, failing septic systems and agricultural areas can contaminate drinking water and close down swimming and shellfish areas. A group of bacteria called fecal coliform bacteria are typically used as the indicators for all bacteria and viruses, so large amounts of fecal coliform may indicate serious problems. 1.2.7 Nutrients In the context of water quality, nutrients are mainly compounds of nitrogen and phosphorus. When nutrients are allowed to enter waterbodies, undesirable effects such as algae overgrowth, oxygen depletion, channel clogging due to overgrowth of vegetation, and fish and animal death can occur. Sources of nutrients can include fertilizers, failing septic systems, and yard and animal wastes. 1.2.8 Toxic Organic Compounds A number of organic chemicals are just plain toxic when they get into the aquatic environment. Pesticides, herbicides, rodenticides, and fungicides are deadly to aquatic life. Compounds such as antifreeze, wood preservatives, cleansers, and a host of other, more exotic organics derived from industries or past practices (such as polychlorinated biphenyls (PCBs), DDT, and chlordane) can also have detrimental effects on the environment. 1.2.9 Other Chemicals and Substances There are a host of other chemicals that can cause problems if allowed to enter the aquatic environment. Common household bleach can be deadly to fish and other critters if drained directly to waterbodies. Diatomaceous earth backwash from swimming pool filters can clog gills and suffocate fish. Arsenic has been used in rat and mole killing compounds. Even those compounds classified as biodegradable or environmentally friendly can have immediate devastating effects on aquatic life. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Frequently Asked Questions Volume IV 4 60 Chapter 1 1.3 Types of Source Control BMPs As the name implies, source control BMPs prevent contamination from entering stormwater runoff by controlling them at the source. There are two categories of source control BMPs: • Operational BMPs • Structural BMPs 1.3.1 Operational BMPs Operational source control BMPs are considered to be the most cost effective pollutant minimization practices. Operational source control BMPs are non-structural practices that prevent or reduce pollutants form entering stormwater. They can also include process changes such as raw material/product changes and recycling wastes. Examples include: • Formation of a pollution prevention team • Good housekeeping practices • Preventive maintenance procedures • Spill prevention and cleanup • Employee training • Inspections of pollutant sources • Record keeping 1.3.2 Structural BMPs Structural source control BMPs are physical, structural or mechanical devices or facilities that are intended to prevent pollutants from entering stormwater. Examples of structural source control BMPs typically include: • Enclosing and/or covering the pollutant source, i.e., within a building or other enclosure, a roof over storage and working areas, a temporary tarp • Physically segregating the pollutant source to prevent run-on of uncontaminated stormwater • Devices that direct only contaminated stormwater to appropriate treatment BMPs, i.e. discharge to a sanitary sewer if allowed by the local sewer utility. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 1 If any of these activities occur indoors, then BMPs are not required, provided no indoor drains or processes can ultimately contact stormwater or be transported to surface waters such as rivers and streams. Ensure that liquids, powders, dusts and fine granular materials stay confined indoors. Otherwise BMPs will be required. 2 If any of these activities occur outdoors, then use the activity code to find the appropriate BMPs described in Chapter 4. Worksheet for Commercial Volume IV and Industrial Activities 461 Chapter 2 Chapter 2 Worksheet for Commercial and Industrial Activities This worksheet is designed for use by business and industry operators. Complete the entire worksheet by checking the appropriate boxes for all activities that take place at the work site. If any of the activities as being performed outdoors, use the activity code on the worksheet to find the recommended BMPs contained in Chapter 4. Are you involved in this? If so, check if it occurs: Activity Code (BMP) TYPE OF ACTIVITY Indoors1 Outdoors2 SECTION A1 – CLEANING AND WASHING ACTIVITIES A101 Cleaning or Washing of Tools, Engines, and Manufacturing Equipment – includes parts washers and all types of manufactured equipment components. A102 Cleaning or Washing of Cooking Equipment – includes vents, filters, pots and pans, grills, and related items. A103 Washing, Pressure Washing, and Steam Cleaning of Vehicles/Equipment /Building Structures – covers cleaning and washing at all types of establishments, including fleet vehicle yards, car dealerships, car washes, and maintenance facilities. A104 Collection and Disposal of Wastewater from Mobile Interior Washing Operations – includes carpet cleaners, upholstery cleaners, and drapery cleaners. SECTION A2 – TRANSFERS OF LIQUID OR SOLID MATERIALS A201 Loading and Unloading Areas for Liquid or Solid Material – for loading and unloading of materials at industrial and commercial facilities A202 Fueling at Dedicated Stations – includes gas stations, pumps at fleet vehicle yards or shops, and other privately owned pumps. A203 Vehicle Maintenance Activities – covers oil changes and other engine fluids. A204 Mobile Fueling of Vehicles and Heavy Equipment – includes fleet fueling, wet fueling, and wet hosing S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 1 If any of these activities occur indoors, then BMPs are not required, provided no indoor drains or processes can ultimately contact stormwater or be transported to surface waters such as rivers and streams. Ensure that liquids, powders, dusts and fine granular materials stay confined indoors. Otherwise BMPs will be required. 2 If any of these activities occur outdoors, then use the activity code to find the appropriate BMPs described in Chapter 4. Worksheet for Commercial Volume IV and Industrial Activities 462 Chapter 2 Are you involved in this? If so, check if it occurs: Activity Code (BMP) TYPE OF ACTIVITY Indoors1 Outdoors2 SECTION A3 – PRODUCTION AND APPLICATION ACTIVITIES A301 Concrete and Asphalt Mixing and Production at Stationary Sites – applies to mixing of raw materials on-site to produce concrete or asphalt. A302 Concrete Pouring, Concrete Cutting, and Asphalt Application at Temporary Sites – includes construction sites, and driveway and parking lot resurfacing. A303 Manufacturing and Post-processing of Metal Products – includes machining, grinding, soldering, cutting, welding, quenching, rinsing, etc. A304 Wood Treatment Areas – includes wood treatment using pressure processes or by dipping or spraying. A305 Commercial Composting – includes commercial composting facilities operating outside. A306 Landscaping and Lawn/Vegetation Maintenance, Including Vegetation Removal, Herbicide and Insecticide Application, Fertilizer Application, Irrigation, Watering, Gardening, and Lawn Care – includes businesses involved in landscaping, applying pesticides and managing vegetation. A307 Painting, Finishing, and Coating of Vehicles, Boats, Buildings, and Equipment – includes surface preparation and the applications of paints, finishes, and/or coatings. A308 Commercial Printing Operations – includes materials used in the printing process. A309 Manufacturing Activities (Outside) -includes outdoor manufacturing areas. SECTION A4 – STORAGE ACTIVITIES A401 Storage or Transfer (Outside) of Solid Raw Materials, By-products, or Finished Products A402 Storage and Treatment of Contaminated Soils – applies to contaminated soils that are excavated and left on-site. A403 Temporary Storage or Processing of Fruits or Vegetables – includes processing activities at wineries, fresh and frozen juice makers, and other food and beverage processing operations. A404 Storage of Solid Wastes and Food Wastes – includes regular garbage and all other discarded non-liquid items. A405 Recyclers and Scrap Yards – includes scrapped equipment, vehicles, empty metal drums, and assorted recyclables. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 1 If any of these activities occur indoors, then BMPs are not required, provided no indoor drains or processes can ultimately contact stormwater or be transported to surface waters such as rivers and streams. Ensure that liquids, powders, dusts and fine granular materials stay confined indoors. Otherwise BMPs will be required. 2 If any of these activities occur outdoors, then use the activity code to find the appropriate BMPs described in Chapter 4. Worksheet for Commercial Volume IV and Industrial Activities 463 Chapter 2 Are you involved in this? If so, check if it occurs: Activity Code (BMP) TYPE OF ACTIVITY Indoors1 Outdoors2 A406 Treatment, Storage, or Disposal of Dangerous Wastes – Refer to Ecology and the appropriate County Health Department for more information, see Chapter 6. A407 Storage of Liquid, Food Waste, or Dangerous Waste Containers – includes containers located outside a building and used for temporary storage A408 Storage of Liquids in Permanent Above-ground Tanks – includes all liquids in above-ground tanks A409 Parking and Storage for Vehicles and Equipment – includes public and commercial parking lots SECTION A5 – CONSTRUCTION ACTIVITIES A501 Clearing, Grading, and Preparation of Construction Sites – applies to land developing activities and to residential yard clearing and grading projects. A502 Demolition of Buildings – applies to removal of existing buildings and subsequent clearing of the rubble. A503 Building Repair, Remodeling, and Construction – applies to construction of buildings, general exterior building repair work and remodeling of buildings. SECTION A6 – DUST CONTROL AND SOIL AND SEDIMENT CONTROL A601 Dust Control at Disturbed Land Areas and Unpaved Roadways and Parking Lots A602 Dust Control at Manufacturing Sites – includes grain dust, sawdust, coal, gravel, crushed rock, cement, and boiler fly ash. A603 Soil Erosion and Sediment Control at Industrial Sites – includes industrial activities that that take place on soil. SECTION A7 – OTHER ACTIVITIES A701 Commercial Animal Handling Areas – includes kennels, fenced pens, veterinarians, and businesses that board animals A702 Log Sorting and Handling – applies to log yards typically located at sawmills, ports, and pulp mills. A703 Boat building, Mooring, Maintenance, and Repair – includes all types of maintenance, repair, and building operations. A704 Logging – applies to logging activities that fall under Class IV general forest practices. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 1 If any of these activities occur indoors, then BMPs are not required, provided no indoor drains or processes can ultimately contact stormwater or be transported to surface waters such as rivers and streams. Ensure that liquids, powders, dusts and fine granular materials stay confined indoors. Otherwise BMPs will be required. 2 If any of these activities occur outdoors, then use the activity code to find the appropriate BMPs described in Chapter 4. Worksheet for Commercial Volume IV and Industrial Activities 464 Chapter 2 Are you involved in this? If so, check if it occurs: Activity Code (BMP) TYPE OF ACTIVITY Indoors1 Outdoors2 A705 Mining and Quarrying of Sand, Gravel, Minerals, Peat, Clay, Rock, and Other Materials – does not include excavation at construction sites. A706 Swimming Pool and Spa Cleaning and Maintenance – includes every swimming pool and spa not at a single family residence. Commercial pool cleaners are included here for all pools. A707 Deicing and Anti-icing Operations for Airports and Streets -includes aircraft, runways/taxiways, streets and highways. A708 Roof and Building Drains at Manufacturing and Commercial Buildings – These sites will be referred to the Puget Sound Clean Air Agency. A709 Urban Streets – includes recommended BMPs. A710 Railroad Yards A711 Maintenance of Public and Private Utility Corridors and Facilities – includes public and private utility maintenance activities. A712 Maintenance of Roadside Ditches A713 Maintenance of Stormwater Drainage and Treatment Facilities A714 Spills of Oil and Hazardous Substances A715 Water Reservoir, Transmission Mainline, Wellhead, and Hydrant Flushing Activities SECTION S1 – SOURCE CONTROL BMPs S101 Eliminate Illicit Sewer to Storm Drainage System Connections S102 Dispose of Contaminated Stormwater and Waste Materials Properly S103 Discharge Process Wastewater to a Sanitary Sewer, Holding Tank, or Water Treatment System S104 Cover the Activity with a Roof of of Awning S105 Cover the Activity with an Anchored Tarp or Plastic Sheet S106 Pave the Activity Area and Slope to a Sump or Holding Tank, or Oil/Water Generator S107 Surround the Activity Area with a Curb, Dike, or Berm or Elevate the Activity S108 Implement Integrated Pest Management Measures S109 Cleaning Catch Basins S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 65 Chapter 3 Chapter 3 BMPs for Homeowners Actions taken each day in and around homes have a profound effect on surface water quality and fish habitat in this region. Stormwater goes directly to rivers, streams and to Puget Sound. Stormwater does not go to the wastewater treatment plant. Any pollutants that get into the stormwater go directly to surface water. Small amounts of pollution from many different sources can significantly affect our waterways. Yard maintenance, waste storage, car washing and maintenance, and pool cleaning are some of the activities that can adversely impact water quality. The best management practices (BMPs) discussed in this section are practical ways to keep stormwater from becoming polluted in the first place. It is recommended that all residents in Auburn use these BMPs. Please note that some of these procedures are required by various state, or city laws, and are noted as required BMPs. A general list of BMPs for homeowners is described in this chapter. Some of the BMPs described in Chapter 4 may also be applicable to homeowners. • Section 3.1 – Automobile Washing • Section 3.2 – Automobile Maintenance • Section 3.3 – Storage of Solid Wastes and Food Wastes • Section 3.4 – Composting • Section 3.5 – Yard Maintenance and Gardening • Section 3.6 – Swimming Pool and Spa Cleaning and Maintenance • Section 3.7 – Household Hazardous Material Use, Storage, and Disposal • Section 3.8 – General Home Maintenance 3.1 Automobile Washing (for Single-Family Residences) Car washing at home will cause wash water to enter the storm system and flow untreated into surface waters. Soaps and detergents, even the biodegradable ones, can have immediate and longterm effects. 3.1.1 Suggested BMPs 3.1.1.1 At Home • Wash cars directly over lawn areas or make sure the wash water drains to a vegetated area. • Ideally, no soaps or detergents should be used, but if one is used, select one without phosphates. • Consider using commercial products that allow cleaning a vehicle without water. • Use a hose nozzle with a shut-off valve to save water. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 66 Chapter 3 • Do not wash cars if rain is expected. • Pour the bucket of soapy, dirty wash water down your sink. 3.1.1.2 Away from Home • Take cars to a commercial car wash that has a recycle system and discharges wastewater to the sanitary sewer for treatment. • Go to fundraising car washes where sponsors use Auburn’s Car Wash loaner kits. Use a Car Wash loaner kit. If your group is planning a car wash in Auburn, call (253) 931-3010 to get information about using a Car Wash loaner kit. 3.2 Automobile Maintenance 3.2.1 Required BMPs • Recycle all oils, antifreeze, solvents, and batteries. Many local car parts dealers and gas stations accept used oil. The King County Household Hazardous Wastemobile makes regular, scheduled visits to Auburn and accepts oil, oil filters, antifreeze, and solvents, (website: http://www.govlink.org/hazwaste/house/disposal/AnyProduct.cfm?catID=974 or call 206-296-4692). 4692). Old batteries can actually be worth money. Recycle old batteries at automotive or battery shops. • Never dump new or used automotive fluids or solvents on the ground, in a storm drain or street gutter, or in a waterbody. • Do not mix wastes. Always keep your wastes in separate containers which are properly labeled and store them out of the weather. 3.2.2 Suggested BMPs • Fix all leaks, to keep the leaky material off the streets and out of the surface water. • To dispose of oil filters, punch a hole in the top and let drain for 24 hours. After draining, wrap in 2 layers of plastic and dispose of in your regular garbage or recycle by taking it to the King County Household Hazardous Waste Wastemobile. Pending State law may make disposal in your home garbage illegal, so please call the King County Household Hazards Line at (206) 296-4692 for up-to-date information. • Use care in draining and collecting antifreeze to prevent accidental spills. Spilled antifreeze can be deadly to cats and dogs that ingest it. • Perform service activities on concrete or asphalt or over a plastic tarp to make spill clean-up easier. Keep a bag of kitty litter on hand to absorb spills. Sprinkle a good layer on the spill, let it absorb and then sweep it up. Place the contaminated litter in a double plastic bag (bag in a bag), tie it up, and dispose of it in your regular garbage. Do not leave kitty litter out in the rain. • If body work is performed outside, be sure to use a tarp to catch material resulting from grinding, sanding, and painting. Dispose of this waste by double bagging in plastic and placing in garbage. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 67 Chapter 3 3.3 Storage of Solid Wastes and Food Wastes Improper storage of food and solid waste at residences can lead not only to water pollution problems, but problems with neighborhood pets and vermin as well. Following the BMPs listed below can help keep property a clean and healthy place to live. 3.3.1 Suggested BMPs • All waste containers kept outside should have lids. If the hauler container lid is damaged, please call the City of Auburn Utilities at (253) 931-3038 for information on lid repair and replacement. • Leaking waste containers should be replaced. If the container is damaged, please call City of Auburn Utilities at (253) 931-3038. • Store waste containers under cover if possible, or on grassy areas. • Inspect the storage area regularly to pick up loose scraps of material and dispose of them properly. • Recycle as much as you can. The City of Auburn offers curbside recycling. Also, look under "Recycling" in the phone book for firms which take other recyclables or call the City of Auburn Solid Waste Division at (253) 931-3047. • Purchase products which have the least amount of packaging materials. • Recycle biodegradable materials such as grass clippings and vegetable scraps in your yard waste cart instead of throwing them away. Call the City of Auburn Utilities at (253) 931-3038 for more information on yard and food scrap recycling. 3.4 Composting Composting is an earth-friendly activity as long as the rules outlined below are followed. The following BMPs are applicable to composting. For more information go to the City of Auburn’s website at www.auburnwa.gov or call the City of Auburn Solid Waste Division at (253) 931-3047. 3.4.1 Suggested BMPs • Locate compost bins on an unpaved area that is not prone to water ponding during storms, and well away from wetlands, streams, lakes and other drainage paths. • Compost bins must be maintained and turned over regularly to work properly. Large piles of unattended compost may create odor and vermin problems and are not allowed within City limits. • Do not put hazardous or non-decomposable waste in the bin. • Cover the bin to keep excess water from cooling down the pile, which will slow down the rate of decomposition. • An alternative to traditional backyard composting is worm composting. For more information on getting started with worm composting, call the City of Auburn Solid Waste Division at (253) 931-3047. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 68 Chapter 3 3.5 Yard Maintenance and Gardening This section deals with the normal yard maintenance activities typically performed at residences. Overwatering, overfertilizing, improper herbicide application, and improper disposal of trimmings and clippings can all contribute to serious water pollution problems. Following the BMPs listed below will help alleviate pollutant runoff. 3.5.1 Required BMPs Follow the manufacturer's directions exactly for mixing and applying herbicides, fungicides, and pesticides, and use them sparingly. Never apply when it is windy or when rain is expected. Never apply over water, within 100 feet of a well-head, or adjacent to streams, wetlands, or other waterbodies. Triple-rinse empty containers, using the rinsate for mixing your next batch of spray, and then double-bag and dispose of the empty container in your regular garbage. Never dispose of grass clippings or other vegetation in or near storm drains, streams, lakes, or Puget Sound. 3.5.2 Suggested BMPs • Use natural, organic soil amendments. Visit www.kingcounty.gov/environment. Click on Composting, Natural Lawn Care for natural yard care information. • Use an integrated pest management program (IPM), which is a natural, long-term, ecologically based approach to controlling pest populations. See Section 4.4.6 and Appendix C – Example of an Integrated Best Management Program. • Follow manufacturer's directions when applying fertilizers. More is not better, either for your lawn or for local waterbodies. Never apply fertilizers over water or adjacent to ditches, streams, or other water bodies. Remember that organic fertilizers have a slow release of nitrogen, and less potential to pollute then synthetic fertilizers. • Save water and prevent pollution problems by watering lawns sensibly. Lawns and gardens typically need the equivalent of 1-inch of rainfall per week. Put a wide mouth jar out where watering is occurring, and measure the water with a small plastic ruler. Overwatering to the point of runoff can carry polluting nutrients to the nearest waterbody. • Consider using native plants as a vegetated buffer zone adjacent to streams or other water bodies. Call the Garden hotline at 206-633-0224 for advice and assistance in developing a planting plan or visit www.kingcounty.gov/Envir onment, Click on Compost, Plant Right for Your Site. • Reduce the need for pesticides and fertilizers on lawns by improving the health of the soil. Aerating, thatching, and topdressing with compost will improve soil health and help wanted grasses compete with weeds and moss. • Make sure all fertilizers and pesticides are stored in a covered location. • Use a mulching mower and mow higher to improve soil/grass health and reduce or eliminate pesticide use. • Compost all yard clippings, or use them as mulch to save water and keep down weeds in your garden. See Composting section for more information. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 69 Chapter 3 • Practice organic gardening and virtually eliminate the need to use pesticides and fertilizers. Contact King County Master Gardener Phone Clinic at 206-296-3440 for information and classes on earth-friendly gardening. • Pull weeds instead of spraying and get some healthy exercise, too. If you must spray, use the least toxic formulations that will get the job done. The Master Gardener program listed above can help advise you on which spray to use. • Work fertilizers into the soil instead of letting them lie on the ground surface exposed to the next rain storm. • Plant vegetation suited to Northwest conditions because they require less water and fewer to no fertilizers and pesticides. • The City of Auburn has a curbside yard waste recycling program. Call 253-931-3038 for more information. 3.6 Swimming Pool and Spa Cleaning and Maintenance Despite the fact that we immerse ourselves in it, the water from pools and spas is far from chemically clean. Nutrients, pH, and chlorine can adversely affect fish and wildlife in waterbodies. Following these BMPs will ensure the cleanliness of your pool and the environment. 3.6.1 Required BMPs • Pool and spa water must be dechlorinated if it is to be emptied into a ditch, on the ground or a lawn, or to the storm drainage system. Contact a pool chemical supplier to obtain the neutralizing chemicals needed. The rate of flow into the ditch or drainage system must be regulated so that it does not cause problems such as erosion, surcharging, or flooding. Contact the City of Auburn Strom Drainage Utility at 253-931-3010 for any conditions for discharge approval. Water discharged to the ground or a lawn must not cross property lines and must not produce runoff. • If pool and spa water cannot be dechlorinated, it must be discharged to the sanitary sewer. Prior to draining a pool or spa, contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for any conditions for discharge approval. A pool service company can help determine the frequency of cleaning and backwash of filters. • Diatomaceous earth used in pool filters cannot be disposed of in surface waters, on the ground, or into storm drainage systems or septic systems. Dry it out as much as possible, bag it in plastic, and dispose of at the landfill. 3.6.2 Suggested BMPs • Hire a professional pool service company to collect all pool water for proper disposal. Make sure to ask where the water will be disposed of and ensure the proper permits have been obtained. 3.7 Household Hazardous Material Use, Storage, and Disposal Oil-based paints and stains, paint thinner, gasoline, charcoal starter fluid, cleaners, waxes, pesticides, fingernail polish remover, and wood preservatives are just a few hazardous materials typically used in a residential setting. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 70 Chapter 3 When hazardous materials are dumped on the ground or in a storm drain, they can be washed directly to receiving waters where fish and wildlife can be harmed. Hazardous materials can also infiltrate into the ground and contaminate drinking water supplies. If disposed of with regular garbage, hazardous chemical containers can leak at the landfill and contaminate groundwater. Groundwater contamination can also occur if hazardous products are poured down a sink or toilet into a septic system. Do not pour hazardous chemicals down the drain if household plumbing is connected to municipal sewers, either. Many compounds will "pass through" the wastewater treatment plant without treatment and contaminate receiving waters, or they can harm the biological process used at the treatment plant, reducing overall treatment efficiency. With such a diversity of hazardous products present in all homes in Auburn, a large potential for serious environmental harm exists if improper methods of storage, usage, and disposal are employed. Using the following BMPs will help keep these materials out of soils, sediments, and waters. 3.7.1 Required BMPs • Hazardous materials must be stored out of the reach of children. • Dispose of hazardous materials and their containers properly. Never dump products labeled as poisonous, corrosive, caustic, flammable, inflammable, volatile, explosive danger, warning, caution, or dangerous outdoors, in a storm drain, or into sinks, toilets or drains. Call the King County Hazardous Waste Line at 206-296-4692 or 1-888-TOXIC ED for information on disposal methods, collection events, and alternative products. Household hazardous wastes from City of Auburn residents are accepted at King County Household Hazardous Waste Facilities. 3.7.2 Suggested BMPs • Check hazardous material containers frequently for signs of leakage. If a container is rusty and has the potential of leaking soon, place it in a secondary container before the leak occurs and prevent a clean-up problem. • Store hazardous materials containers under cover and off the ground. Keep them out of the weather to avoid rusting, freezing, cracking, labels being washed off, etc. • Keep appropriate spill cleanup materials on hand. Kitty litter is good for many oilbased spills. • Ground cloths and drip pans must be used under any work outdoors which involves hazardous materials such as oil-based paints, stains, rust removers, masonry cleaners, and others bearing label warnings as outlined above. • Latex paints are not a hazardous waste, but are not accepted in liquid form at the landfill. To dispose, leave uncovered in a protected place until dry, then place in the garbage. If you wish to dry waste paint quickly, just pour kitty litter in the can to absorb the paint. Once paint is dry, leave the lid off when you place it in the garbage so the garbage collector can see that it is no longer liquid. • Use less toxic products whenever possible. The King County Household Hazards Line at 206-296-4692 or 1-888-TOXIC ED and the Washington Toxics Coalition at 206-632-1545 have information detailing alternatives to toxic products. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Homeowners Volume IV 4 71 Chapter 3 • If an activity involving the use of a hazardous material can be moved indoors out of the weather, then do so. Make sure proper ventilation is provided. • Follow manufacturers' directions in the use of all materials. Over-application of yard chemicals, for instance, can result in the washing of these compounds into receiving waterbodies. Never apply pesticides when rain is expected. • When hazardous materials are in use, place the container inside a tub or bucket to minimize spills. • Purchase only the amount of product that is needed. 3.8 General Home Maintenance This section deals with the normal maintenance activities typically performed in residential settings. Following the BMPs listed below will help alleviate pollutant runoff. 3.8.1 Suggested BMPs Pressure washing of building facades, rooftops, pavement, and other large objects must be conducted in such a way that all of the runoff is collected for proper disposal. No runoff shall leave the site. Temporary curbs, dikes, or berms may be used to direct the water away from storm drains. Sweep up and collect debris for disposal as solid waste as an alternative to pressure washing. Carpet cleaning wash water must be disposed of to the sanitary sewer. It is preferred that the dirty wash water be discharged into a toilet or mop sink at the place where it was generated. Clean brushes and tools coated with non-water-based paints, finishes, or other materials in a manner that allow collection of used solvents (e.g. paint thinner, turpentine, xylol, etc.) for proper disposal at a Household Hazardous Waste Facility. Call the King County Household Hazards Line at 206-296-4692 or 1-888-TOXIC ED for information on disposal methods, collection events, and alternative products. Household hazardous wastes from City of Auburn residents are accepted at King County Household Hazardous Waste Facilities. 3.9 Pet Waste Pets can generate pollutants from manure deposits, animal washing, and cage or kennel cleaning. Pollutants include bacteria which can pollute water ways and make people sick. To prevent pet waste pollutants from entering the storm drains, follow the BMPs listed below. 3.9.1 Suggested BMPs • Regularly scoop, sweep and clean up pet waste deposited on walks and at home. Dispose of pet waste in the garbage or flush it down the toilet. • When cleaning out cages and kennels, wash directly over lawn areas or make sure the wash water drains to a vegetated area. Alternately, dispose of the wash water down the toilet or a mop sink. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 72 Chapter 4 Chapter 4 BMPs for Commercial and Industrial Activities This chapter coordinates with the worksheet completed in Chapter 2. That worksheet and the BMPs are organized by the different activities that businesses perform. If the listed activity is performed indoors and all discharges from the activity are controlled (e.g., process water, wash water, lubricants, solvents, fugitive dust, granular material, blowdown waste, etc.) such that no exposure to stormwater occurs, then no new BMPs for that activity are required. However, if the column for activities performed outdoors was checked, match the number from the worksheet to the activities listed in this section to find the BMPs suggested. Contact the City’s Storm Drainage Utility at 253-931-3010 for more information or technical assistance. Assistance can be provided over the phone or at on-site consultations. Every person/business in Auburn is required to use BMPs as outlined in this manual. Utilizing additional BMPs to protect water further quality is encouraged. Some businesses are or will be required to obtain a National Pollutant Discharge Elimination System (NPDES) permit for stormwater discharges. These permits are issued and regulated by the Washington State Department of Ecology. There are several BMPs contained in this chapter that may also apply to residences and other noncommercial or non-industrial sites. 4.1 BMPs to Consider for all Activities Some common best management practices that should be considered for all activities include: • Avoid the activity or reduce its occurrence. • Move the activity indoors if possible. • Clean up spills quickly. • Use less material. • Use the least toxic materials available. • Create and maintain vegetated areas near activity locations. • Locate activities as far as possible from surface drainage paths. • Keep storm drain systems clean. • Reduce, reuse, and recycle as much as possible. • Be an advocate for stormwater pollution prevention. • Report violators to Storm Drainage Utility 253-931-3010. • Provide oversight and training. • Sweep or vacuum to control dust and debris. • Regularly inspect, clean, and repair all facilities and BMPs. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 73 Chapter 4 4.2 Cleaning and Washing Activities 4.2.1 BMP A101: Cleaning or Washing of Tools, Engines and Manufacturing Equipment 4.2.1.1 Description of Pollutant Sources This activity applies to businesses and public agencies that clean manufacturing equipment such as saws, grinders, screens, and other processing devices outside of buildings, and to businesses engaged in pressure washing of engines, equipment, and portable objects. Pollutants sources include toxic hydrocarbons, organic compounds, oils and greases, nutrients, heavy metals, pH, suspended solids, biochemical oxygen demand (BOD), and chemical oxygen demand (COD). 4.2.1.2 Pollutant Control Approach The preferred approach is to cover and/or contain the cleaning activity or conduct the activity inside a building, to separate the uncontaminated stormwater from the pollutant sources. Wash water must be conveyed to a sanitary sewer after approval by the City of Auburn, temporarily stored before proper disposal, or recycled, with no discharge to the ground, a storm drain, or surface water. Washwater may be discharged to the ground after proper treatment in accordance with Ecology Guidance WQR-95-56, “Vehicle and Equipment Washwater Discharges,” revised September 2007. The quality of any discharge to the ground after proper treatment must comply with Ecology’s Groundwater Quality Standards, Chapter 173-200 WAC. Contact the Ecology Southwest Regional Office for an NPDES Permit application for discharge of washwater to surface water or to a storm drain after on-site treatment. 4.2.1.3 Required BMPs The following BMPs, or equivalent measures, are required of all businesses and public agencies engaged in cleaning or washing of tools, engines, equipment, and portable objects: • Illicit connections to the storm drainage system must be eliminated. See BMP S101 for detailed information. • Employees shall be educated to control washing operations to prevent stormwater contamination. • All washwater must discharge to a holding tank, process treatment system, or sanitary sewer, never to the storm drain system. See BMP S103 for detailed information on how this must be accomplished. • Pressure washing must be done in a designated area (such as a wash pad) provided with a sump drain and stormwater run-on prevention (Figure IV-4-1). See BMPs S106 and S107 for information on sumps (or holding tanks) and run-on prevention. Contact the City of Auburn Storm Drainage Utility at 253-931-3010 for washing operation policy. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 74 Chapter 4 Figure IV-4-1. Pressure Wash Water Recovery System 4.2.1.4 Recommended BMPs The following BMPs are not required, but they can provide additional pollution control: • If soaps or detergents are used, use the least toxic cleaner capable of doing the job. Use non-phosphate detergent, if possible, to reduce loadings at your local wastewater treatment plant. • Limit the amount of water used in washing activities to reduce the potential of runoff carrying pollutants beyond the designated wash pad or capture system. • Recycle washwater for subsequent washings. • Implement one or more of the following stormwater treatment BMPs in addition to the Required BMPs: o Oil/water separator (do not use an oil/water separator for wash water containing soaps or detergents). o Wet vault for settling. o Infiltration basin. o Filtration with media designed for the pollutants present. o Catch basin with a filter insert for pressure washing to collect suspended solids. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 75 Chapter 4 • Catch basin filters and/or sorbent inserts should be selected based on the type of contaminants in the stormwater. For discharging washwater containing soaps and detergents, the use of infiltration, biofiltration, wet ponds, and wetlands must not result in the violation of groundwater quality standards. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 76 Chapter 4 4.2.2 BMP A102: Cleaning or Washing of Cooking Equipment 4.2.2.1 Description of Pollutant Sources This activity applies to businesses that clean cooking equipment such as vent filters, grills, hoods, and grease traps outside of buildings and clean paved areas and floor mats around cooking equipment. Pollutants of concern consist of oil and grease, nutrients, suspended solids, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) 4.2.2.2 Pollutant Control Approach Businesses engaged in this activity that cannot connect discharges to a sanitary sewer, holding tank, or process water treatment system must contact the Department of Ecology and obtain a National Pollutant Discharge Elimination System (NPDES) wastewater permit. 4.2.2.3 Required BMPs The following BMPs or equivalent measures are required of all businesses engaged in cleaning or washing of cooking equipment: • Illicit connections to the storm drainage system must be eliminated. See BMP S101 for detailed requirements. • Employees must be educated about the need to prevent stormwater contamination from washing operations. • Washwater cannot be discharged to the storm drainage system. • Paved washing areas must be swept daily to collect loose solid materials for proper disposal. • Greasy buildup on cooking equipment must be removed and properly disposed of prior to washing to reduce the amount of material that can potentially contaminate runoff. Washing must either take place on a wash pad connected to the sanitary sewer, or the wastewater must be collected and disposed in the sanitary sewer. • Move the activity indoors, into either an existing building or a newly constructed building or shed, with drainage to a sanitary sewer, holding tank, or process treatment system. See BMP S103 for further information on drainage alternatives. Any connection to the sanitary sewer requires the approval of the the City of Auburn. If the washing activity cannot be moved indoors or contained in a tub, then the washing area must drain to a sanitary sewer, holding tank, or process treatment system, and provisions must be made to prevent stormwater run-on onto the washing area. See BMP S103 for detailed drainage requirements and BMP S107 for methods of run-on prevention. If discharging to a sanitary sewer, permits must be obtained from the City of Auburn Permit Center 253-931-3090. OR S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 77 Chapter 4 Use a tub or similar device to contain washwater. This water must be recycled for subsequent washing, or disposed into a holding tank or sanitary sewer. • If a holding tank is used for storage of washwater, the contents must be pumped out before it is full and disposed of appropriately to a sanitary sewer or wastewater treatment system. 4.2.2.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • A cover should be placed over a designated wash area to keep rain from falling on dirty equipment and producing contaminated runoff. • Implement one or more of the following treatment BMPs in addition to the required BMPs: o Oil/water separator. o Wet vault for settling. o Infiltration basin with pretreatment. o Filtration with media designed for the pollutants present. For discharging washwater containing soaps and and detergents, the use of infiltration, biofiltration, wet ponds, and wetlands must not result in the violation of groundwater quality standards. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 78 Chapter 4 4.2.3 BMP A103: Washing, Pressure Washing and Steam Cleaning of Vehicles/Equipment/Building Structures 4.2.3.1 Description of Pollutant Sources Vehicles, aircraft, vessels/boats, grocery carts, carpets, industrial equipment, and large buildings or structures may be commercially cleaned with low or high pressure water or steam. This also includes removing graffiti and “charity” car washes at gas stations and commercial parking lots. The cleaning can include hand washing, scrubbing, sanding, etc. Washwater from cleaning activities can contain oil and grease, suspended solids, heavy metals, soluble organics, soaps, and detergents that can contaminate stormwater. 4.2.3.2 Pollutant Control Approach The preferred approach is to cover and/or contain the cleaning activity, or conduct the activity inside a building, to separate the uncontaminated stormwater from the pollutant sources. Washwater must be conveyed to a sanitary sewer after approval by the City of Auburn. See Ecology guidance WQ-R-95-56, “Vehicle and Equipment Washwater Discharges,” June 1995 for more information. 4.2.3.3 Required BMPs: New and Used Car Dealer Lots If washing is accomplished only with cold water and consists of washing only the outside of the motor vehicles, (no soaps or detergents used) there should be no discharge to the sanitary sewer. See Ecology guidance WQ-R-95-56, “Vehicle and Equipment Washwater Discharge”, June 1995, for more information. If soaps or detergents are to be used, washing must occur on a dedicated wash pad. Only the washing of the outside of the vehicles is permitted. The wash pad must be equipped with a catch basin/sediment trap that discharges through a tee outlet to the sanitary sewer. The tee outlet will allow containment of minor amounts of free-floating oil. Wastewater must meet local limitations on wastewater strength and quality. If engines and/or undercarriages undercarriages are to be washed additional pretreatment will be required. Contact the City of Auburn Storm Drainage Utility at 253-931-3010 for further information. The facility will be inspected periodically by City staff. Other Washing Events Identify types of washing events and their locations (such as regional used car sales, RV shows, etc.) and evaluate options on a case-by-case basis according to the discharge criteria stated above. Charity car washes should wash only the exterior of vehicles. If soap is used the wash water must be captured and directed to the sanitary sewer. For information concerning the use of charity car wash kits, contact City of Auburn Public Works Department at 253-931-3010. Pressure washing of building facades, rooftops, pavement, and other large objects must be conducted in such a way that all of the runoff is collected for proper disposal. No runoff shall leave the site. Temporary curbs, dikes, or berms may be used to direct the water to a collection point or catch basins may be covered to help contain the water. The collected water, provided it meets local limits, should be disposed of to the sanitary sewer. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 79 Chapter 4 On a case by case basis, if runoff does not contain pollutants, following appropriate pretreatment, such as filtration or sedimentation, then this water may be allowed to be discharged to the storm drainage system. Contact the City of Storm Drainage Utility at 253-931-3010 for more information. Automatic Car Wash At a minimum, a catch basin/sediment trap that discharges through a tee outlet to the sanitary sewer is required. Other requirements may be necessary on a case-by-case basis. Manual (Wand) Car Wash There must be covered and bermed bays with a catch basin/sediment trap connected to a designed pretreatment device discharging to the sanitary sewer. At a minimum a coalescing plate oil water separator will be required. The facility will be inspected periodically by City staff. Truck Washing Facilities Wash on a concrete or asphalt paved dedicated wash pad pad with a catch basin/sediment trap connected to a designed pretreatment device, which discharges to the sanitary sewer. At a minimum a coalescing plate oil water separator will be required. The facility will be inspected periodically by City staff. Mobile Vehicle Washers The following summarizes the requirements for mobile vehicle and grocery cart washers doing work in the City of Auburn. Contact the City of Auburn Storm Drainage Utility at 253-931-3010 for more information. Mobile vehicle washers must possess a current City of Auburn Business License and they must possess a Letter of Authorization issued by the City’s Storm Drainage Utility. Mobile Vehicle Washers must also: • Discharge all wash water to the sanitary sewer; • Submit MSDS sheets for all chemicals used; • Obtain Source Control approval for any chemicals used; and • Provide adequate means to prevent contaminated wash water from entering the storm drainage system or discharging onto unpaved ground. Mobile vehicle washers may wash only the exteriors of the vehicles. Engine washing, cleaning the undercarriage or fifth wheel is strictly prohibited unless prior approval is received from the Storm Drainage Utility. Additional pretreatment may be required. Discharges from mobile washing must meet City of Auburn code requirement, Chapter 13.20 discharge limitations for pH. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 80 Chapter 4 Those washers employing the two-step (acid-alkaline) process must obtain approval from City of Auburn Sanitary Sewer Utility on a case-by-case basis. At a minimum, two-step washers must: • Provide some means of holding and mixing the wash water generated; • Provide an accepted means of testing the pH of the mixed wash water; • Provide a means of adjusting the pH, if necessary, to within City of Auburn limits; • Discharge the wastewater to the sanitary sewer; or • Capture all of the water and dispose of it at a licensed treatment, storage, and disposal facility. Mobile vehicle washers must discharge wash water to the sanitary sewer system through an on-site cleanout if available. Only wastewater generated within the City of Auburn may be discharged into the municipal sewer system. 4.2.3.4 General Two-step washing may be allowed at all facilities discharging to to the sanitary sewer. Provisions must be in place to neutralize the wash water rinsate prior to introduction into the sanitary sewer system. For facilities with dedicated wash pads with either a catch basin with a tee discharge and/or pretreatment equipment, sampling and monitoring ports will be required. Additionally, the installation of a valve may be required to prevent discharge from the system in the event of a spill. All ports must be accessible for inspection and sampling at all times. Any equipment needed for access must be available at all times. Any sampling and testing required of industry to verify pretreatment equipment performance shall be accomplished by using 40 CFR Part 136 approved methods. For Total Petroleum Hydrocarbons (TPH) EPA Method 1664 may be used. Applicants requesting approval of designed oil/water separator systems must submit three (3) sets of plans. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 81 Chapter 4 4.2.4 BMP A104: Collection and Disposal of Wastewater in Mobile Interior Washing Operations 4.2.4.1 Description of Pollutant Sources This activity applies to businesses that wash carpets and other interior items on a mobile site-to-site basis. The typical washing process includes use of machines that spray the wash water solution onto the carpet or upholstery and then suck the dirty solution up into a portable tank with limited capacity. Pollutants of concern consist of nutrients, suspended solids, organic compounds (such as pesticides and chemicals used for flea and odor control), biochemical oxygen demand (BOD), and chemical oxygen demand (COD). 4.2.4.2 Pollutant Control Approach Wastewater must be poured into a sanitary sewer drain at the site of collection, the business office, or at another proper location. If sanitary sewer disposal is not available or not allowed, the collected wastewater must be returned to the business site for process treatment or transfer to a holding tank. 4.2.4.3 Required BMPs This BMP is required of all businesses doing mobile interior wash activities: • Absolutely no wastewater from mobile interior wash activities shall be disposed of outdoors, or to a drain connected to the storm drainage system. This point must be made clear to all employees. Wastewater from mobile washing operations may be permitted for sanitary sewer disposal if it does not contain high concentrations of toxic materials. Some of the chemicals used for flea and odor control are listed by EPA as toxics. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 if you intend to use and discharge these types of chemicals. All wastewater must be poured into a sanitary sewer drain at the site of collection, the business office, or at another proper location. • If sanitary sewer disposal is not available or not allowed, the collected wastewater must be returned to the business site for process treatment or transfer to a holding tank. See BMP S103 for details on these drainage/disposal alternatives. Carpet cleaning wash water must be disposed of to the sanitary sewer. It is preferred that the dirty wash water be discharged into a toilet or sink at the place where it was generated. Alternatively, the carpet cleaner may discharge the water into the sanitary sewer back at their place of business if located in Auburn. Otherwise, they must contact the sewerage agency providing their service for that agency’s approval. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 82 Chapter 4 4.2.4.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • Use the least toxic detergents and cleaners that will get the job done. Select nonphosphate detergents when possible. • Limit the amount of water used in interior washing operations. This will save you time, money, and effort when it comes to proper disposal. • Recycle washwater for more than one use. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 83 Chapter 4 4.3 Transfer of Liquid or Solid Materials 4.3.1 BMP A201: Loading and Unloading Areas for Liquid or Solid Material 4.3.1.1 Description of Pollutant Sources Loading/unloading of liquid and solid materials at industrial and commercial facilities is typically conducted at shipping and receiving, outside storage, fueling areas, etc. Materials transferred can include products, raw materials, intermediate products, waste materials, fuels, scrap metals, etc. Leaks and spills of fuels, oils, powders, organics, heavy metals, salts, acids, alkalis, etc. during transfer are potential causes of stormwater contamination. Spills from hydraulic line breaks are a common problem at loading docks. 4.3.1.2 Pollutant Control Approach Cover and contain the loading/unloading area where necessary to prevent run-on of stormwater and runoff of contaminated stormwater. 4.3.1.3 Required BMPs At All Loading/Unloading Areas: • A significant amount of debris can accumulate at outside, uncovered loading/unloading areas. Sweep these surfaces frequently to remove material that could otherwise be washed off by stormwater. Sweep outside areas that are covered for a period of time by containers, logs, or other material after the areas are cleared. • Place drip pans or other appropriate temporary containment devices at locations where leaks or spills may occur such as hose connections, hose reels, and filler nozzles. Drip pans shall always be used when making and breaking connections (see Figure IV-4-2). Check loading/unloading equipment such as valves, pumps, flanges, and connections regularly for leaks and repair as needed. Frequent monitoring of drip pans is required to ensure captured materials are not displaced by wind or rainwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 84 Chapter 4 Figure 4.2 – Drip Pan Figure IV-4-2. Drip Pan At Tanker Truck and Rail Transfer Areas to Above/Below-ground Storage Tanks: • To minimize the risk of accidental spillage, prepare an "Operations Plan" that describes procedures for loading/unloading. Train the employees, especially fork lift operators, in its execution and post it or otherwise have it readily available to employees. • Report spills of reportable quantities to Ecology’s Northwest Regional Office 425-649-7000. • Prepare and implement an Emergency Spill Cleanup Plan for the facility (BMP A714 Spills of Oil and Hazardous Substances) which includes the following BMPs: o Ensure the clean up of liquid/solid spills in the loading/unloading area immediately if a significant spill occurs, upon completion of the loading/unloading activity, or at the end of the working day. o Retain and maintain an appropriate oil spill cleanup kit on-site for rapid cleanup of material spills (see BMP A714 Spills of Oil and Hazardous Substances). o Ensure that an employee trained in spill containment and cleanup is present during loading/unloading. At Rail Transfer Areas to Above/Below-ground Storage Tanks: Install a drip pan system as illustrated (see Figure IV-4-3) within the rails to collect spills/leaks from tank cars and hose connections, hose reels, and filler nozzles. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 85 Chapter 4 Figure IV-4-3. Drip Pan Within Rails Loading/Unloading from/to Marine Vessels: Facilities and procedures for the loading or unloading of petroleum products must comply with Coast Guard requirements. Transfer of Small Quantities from Tanks and Containers: Refer to BMPs A408 Storage of Liquids in Permanent Above-Ground Tanks and A407 Storage of Liquid, Food Waste, or Dangerous Waste Containers for requirements on the transfer of small quantities from tanks and containers, respectively. At All Loading/Unloading Areas: • Consistent with Uniform Fire Code requirements and to the extent practicable, conduct unloading or loading of solids and liquids in a manufacturing building or under a roof, lean-to, or other appropriate cover. • Berm, dike, and/or slope the loading/unloading area to prevent run-on of stormwater and to prevent the runoff or loss of any spilled material from the area. • Large loading areas frequently are not curbed along the shoreline. As a result, stormwater passes directly off the paved surface into surface water. Place curbs along the edge, or slope the edge such that the stormwater can flow to an internal storm drain system that leads to an approved treatment BMP. • Pave and slope loading/unloading areas to prevent the pooling of water. The use of catch basins and drain lines within the interior of the paved area must be minimized as they will frequently be covered by material, or they shall be placed in designated “alleyways” that are not covered by material, containers, or equipment. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 86 Chapter 4 4.3.1.4 Recommended BMPs: • For the transfer of pollutant liquids in areas that cannot contain a catastrophic spill, install an automatic shutoff system in case of unanticipated off-loading interruption (e.g. coupling break, hose rupture, overfill, etc.). At Loading and Unloading Docks: • Install/maintain overhangs or door skirts that enclose the trailer end (see Figure IV-4-4 and Figure IV-4-5) to prevent contact with rainwater. • Design the loading/unloading area with berms, sloping, etc. to prevent the run-on of stormwater. • Retain on-site the necessary materials for rapid cleanup of spills. At Tanker Truck Transfer Areas to Above/Below-Ground Storage Tanks: • Pave the area on which the transfer takes place. If any transferred liquid, such as gasoline, is reactive with asphalt, pave the area with Portland cement concrete. • Slope, berm, or dike the transfer area to a dead-end sump, spill containment sump, spill control (SC) oil/water separator, or other spill control device. The minimum spill retention time should be 15 minutes at the highest fuel dispenser nozzle through-put rate or the peak flow rate of the 6-month, 24-hour storm event over the surface of the containment pad, whichever is greater. The volume of the spill containment sump should be a minimum of 50 gallons with an adequate grit sedimentation volume. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 87 Chapter 4 Figure IV-4-4. Loading Dock with Door Skirt Figure 4.5 – Loading Dock with Overhang Figure IV-4-5. Loading Dock with Overhang S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 88 Chapter 4 4.3.2 BMP A202: Fueling at Dedicated Stations 4.3.2.1 Description of Pollutant Sources A fueling station is a facility dedicated to the transfer of fuels from a stationary pumping station to mobile vehicles or equipment. It includes above or under-ground fuel storage facilities. In addition to general service gas stations, fueling may also occur at 24-hour convenience stores, construction sites, warehouses, car washes, manufacturing establishments, port facilities, and businesses with fleet vehicles. Typically, stormwater contamination at fueling stations is caused by leaks/spills of fuels, lube oils, radiator coolants, and vehicle wash water. 4.3.2.2 Pollutant Control Approach New or substantially remodeled fueling stations must be constructed on an impervious concrete pad under a roof to keep out rainfall and stormwater run-on. Substantial remodeling includes replacing the canopy or relocating or adding one or more fuel dispensers in such a way that the Portland cement concrete (or equivalent) paving in the fueling area is modified. A treatment BMP must be used for contaminated stormwater and wastewaters in the fueling containment area. 4.3.2.3 Required BMPs: General Requirements • Fuel islands shall not drain into the storm drainage system. • Fuel islands shall be paved and provide a means to protect the storm drainage and sanitary sewers from spills. • Fuel islands may provide blind sumps for spill containment, or they may drain into the sanitary sewer through a properly sized oil/water separator protected by an emergency shut-off valve. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for assistance. • Fueling areas must encompass the reach of the longest fueling hose. Oil/Water Separator Requirements (see Figure IV-4-6) • Separators shall have as a minimum a 4” diameter tee installed in the discharge line. • Separators shall have an emergency shut-off valve installed on the discharge line. A valve key shall be provided and be prominently displayed near the shut-off valve. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 89 Chapter 4 Figure IV-4-6. Oil/Water Separator Layout Accidental Spill Prevention Plan An Accidental Spill Prevention Plan developed by the operator and approved by Storm Drainage Utility shall be available for inspection. See BMP A714 Spills of Oil and Hazardous Materials for the elements of a spill plan. Covered Fuel Islands • Areas outside the canopy cover shall be sloped or bermed to divert precipitation away from the fuel island and into the storm drainage system. • For a covered fuel island with incidental stormwater run-on and no more than four (4) hose bibs, a minimum 18 gpm rated, 530 gallon capacity oil/water separator (Hanson Pipe Vault 466-S or equivalent) shall be used when connecting to a sanitary sewer. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 90 Chapter 4 • Covered fueling islands must have a roof or canopy to prevent the direct entry of precipitation onto the spill containment pad (see Figure IV-4-7 below). The roof or canopy shall, at a minimum, cover the spill containment pad (within the grade break or fuel dispensing area) and preferably extend several additional feet to reduce the introduction of windblown rain. Convey all roof drains to storm drains outside the fueling containment area. Figure IV-4-7. Covered Fuel Island S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 91 Chapter 4 Uncovered Fuel Islands a. Fuel islands shall be sized to minimize the area which drains to the sanitary sewer. Areas outside the pad shall be sloped to divert precipitation into the storm drainage system. b. Separators used for spill protection with uncovered fuel islands must be sized using standard engineering practices and shall be based on a 25-year storm event (see Table IV-4-1 below). Table IV-4-1. Uncovered Fuel Island Separator Sizing Requirements Calculated Flow (gpm) Separator Size Requirement 18 530 gallon capacity PIPE Vault 466-S, or equivalent 30 900 gallon capacity PIPE Vault 577-S, or equivalent 72 2,160 gallon capacity PIPE Vault 5106-S, or equivalent 108 3,230 gallon capacity PIPE Vault 612-S, or equivalent 126 3,770 gallon capacity PIPE Vault 712-S, or equivalent 182 5,450 gallon capacity PIPE Vault 814-8-S, or equivalent 215 6,460 gallon capacity PIPE Vault 818-8-S, or equivalent NOTE: This sizing is not appropriate for a stormwater quality treatment device. Refer to Volume V, Chapter 9. BMPs Applicable to Both Covered and Uncovered Fuel Islands • Prepare an emergency spill response and cleanup plan (per BMP A714 Spills of Oil and Hazardous Substances) and have designated trained person(s) available either on site or on call at all times to promptly and properly implement that plan and immediately cleanup all spills. Keep suitable cleanup materials, such as dry adsorbent materials, on site to allow prompt cleanup of a spill. • Train employees on the proper use of fuel dispensers. Post signs in accordance with the International Fire Code (IFC). Post “No Topping Off” signs (topping off gas tanks causes spillage and vents gas fumes to the air). Make sure that the automatic shutoff on the fuel nozzle is functioning properly. • The person conducting the fuel transfer must be present at the fueling pump during fuel transfer, particularly at unattended or self-serve stations. • Provide suitable containers for waste materials such as oil filters, oil cans, and garbage. • Design the fueling island to control spills (a spill control oil/water separator in compliance with City of Auburn requirements) and to treat collected stormwater and/or wastewater to required levels. Slope the concrete containment pad around the fueling island toward drains: trench drains or, catch basins. The slope of the drains shall not be less than 1 percent (Section 3405.3.8.1 of the IFC). The outlet from the spill control oil/water separator shall have a shutoff valve, which must be S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 92 Chapter 4 closed in the event of a spill. The spill control sump must be sized using standard engineering practices and shall be based a 25-year storm event when the fueling area is uncovered; or • Design the fueling island as a spill containment pad with a sill or berm raised to a minimum of four inches to prevent the runoff of spilled liquids and to prevent run-on of stormwater from the surrounding area. Raised sills are not required at the opengrate trenches that connect to an approved drainage-control system. • The fueling pad must be paved with Portland cement concrete, or equivalent. Asphalt is not considered an equivalent material. • Stormwater collected on the fuel island containment pad must be conveyed to a sanitary sewer system, as approved by the City of Auburn. In rare cases, stormwater may be conveyed to the storm drainage system through an approved treatment system such as an oil/water separator and a basic treatment BMP (basic treatment BMPs are listed in Volume V and include media filters and biofilters). Discharges from treatment systems to storm drains or surface water or to the ground must not display ongoing or recurring visible sheen and must not contain levels of oil and grease above Water Quality or Model Toxics Control Act criteria. • Alternatively, stormwater collected on the fuel island containment pad may be collected and held for proper off site disposal. • Conveyance of any fuel-contaminated stormwater to a sanitary sewer must be approved by the City of Auburn. All discharge must meet the criteria specified in Auburn City Code Chapter 13.20. • Transfer fuel from the delivery tank truck to the fuel storage tank on an impervious surface and ensure that appropriate overflow protection is used. Use drip pans under all hose connections. Additional BMP for Vehicles 10 feet in height or greater: A roof or canopy may not be practicable at fueling stations that regularly fuel vehicles that are 10 feet in height or greater, particularly at industrial sites. At those types of fueling facilities, the following BMPs apply, as well as all of the other required BMPs and fire code requirements. • The concrete fueling pad must be equipped with emergency spill control, which may include an oil/water separator, with a shutoff valve for the drainage from the fueling area. The valve must be closed in the event of a spill. Spills must be cleaned up and disposed off-site in accordance with BMP A714 Spills of Oil and Hazardous Substances. • Stormwater collected on the fuel island containment pad must be conveyed to a sanitary sewer system, as approved by the City of Auburn. In rare cases, and only when approved by the City, stormwater may be conveyed to the storm drainage system through an approved treatment system such as an oil/water separator and a basic treatment BMP (basic treatment BMPs are listed in Volume V and include S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 93 Chapter 4 media filters and biofilters). Discharges from treatment systems to storm drains or surface water or to the ground must not display ongoing or recurring visible sheen and must not contain levels of oil and grease above Water Quality or Model Toxics Control Act criteria. An explosive or flammable mixture is defined under state and federal pretreatment regulations, based on a flash point determination of the mixture. If contaminated stormwater is determined not to be explosive or flammable, then it could be conveyed to a sanitary sewer system, if approved by the City of Auburn. Figure IV-4-8. Surrounding Activities Containing Oversized Equipment S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 94 Chapter 4 4.3.3 BMP A203: Vehicle Maintenance Activities 4.3.3.1 Description of Pollutant Sources This activity applies to businesses and public agencies where fuel filters, engine oil, and other fluids such as battery acid, coolants, and transmission and brake fluids are removed and replaced in vehicles and equipment. It also applies to mobile vehicle maintenance operations, such as at construction sites. Related vehicle maintenance activities are covered under the following activity headings in this manual, and other BMPs provided in this manual: A103 Washing, Pressure Washing, and Steam Cleaning of Vehicles/Equipment/Building Structures A201 Loading and Unloading Areas for Liquid or Solid Material A202 Fueling at Dedicated Stations A204 Mobile Fueling A307 Painting, Finishing and Coating of Vehicles, Boats, Buildings, and Equipment A401 Storage or Transfer (Outside) Outside) of Solid Raw Materials, By-Products, or Finished Products A407 Storage of Liquid, Food Waste, or Dangerous Waste Containers A408 Storage of Liquids in Permanent Above-ground Tanks A409 Parking and Storage for Vehicles and Equipment A714 Spills of Oil and Hazardous Substances Pollutants of concern include toxic hydrocarbons, toxic organic compounds, oils and greases, pH, and heavy metals. 4.3.3.2 Pollutant Control Approach Control of leaks and spills of fluids using good housekeeping and cover and containment BMPs. 4.3.3.3 Required BMPs The following BMPs or equivalent measures are required of all businesses and agencies engaged in engine and vehicle repair: • Employees must be educated about the need for careful handling of automotive fluids. Employees at businesses or agencies who routinely change or handle these fluids must be trained in spill response and cleanup procedures. Inspect all incoming vehicles, parts, and equipment stored temporarily outside for leaks. • Remove batteries and liquids from vehicles and equipment in designated areas designed to prevent stormwater contamination. Store cracked batteries in a covered non-leaking secondary containment system. • Empty fuel and fuel filters before disposal. • Spill cleanup materials, such as rags and absorbent materials, must always be kept close at hand when changing oil and other fluids. Soiled rags and other cleanup material must be properly disposed of or cleaned and reused. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 95 Chapter 4 • Floor drains inside buildings shall connect to sanitary sewer, be routed through an appropriately sized oil/water separator and shall be approved by the City. • Do not hose down the maintenance/repair area. Instead, sweep the area weekly to collect dirt, and wipe up spills with rags and other absorbent materials. • A bermed tarp, ground cloth, or drip pans must be used beneath the vehicle or equipment to capture all spills and drips. The collected drips and spills must be recycled or disposed of properly. See BMP S102 for disposal options. • If this activity occurs at a stationary business location, the activity area must be moved indoors. An exception to this requirement would be equipment that is too large to fit under a roofed area. In this case, the outdoor area must be paved, provided with a sump drain, and provision made for stormwater run-on prevention. See BMP S106 and S107 for more on paving, sump drains and holding tanks, and run-on prevention. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for information on requirements for disposal to sewer. If the site utilizes a septic tank, sump contents will need to be pumped and disposed of by an oil recycler or hazardous waste company. • Recycle oil, antifreeze, batteries, and air conditioning coolant. • If engine washing is to be performed, then appropriate pretreatment will be required. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for the requirements. • Implement the following treatment BMP in addition to the Required BMPs: • Contaminated stormwater runoff from vehicle staging and maintenance areas must be conveyed to an API or CP oil and water separator followed by a basic treatment BMP (see Volume V), applicable filter, or other equivalent oil treatment system. 4.3.3.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution prevention. • Drain all fluids from wrecked vehicles and car parts upon arrival. Recover air conditioning gases. • Use reusable cloth rags to clean up drips and small spills instead of disposables: these can be professionally laundered and reused. Do not attempt to launder these at home or at a coin-op laundry. • Use absorbent pillows or booms in or around storm drains and catch basins to absorb oil and fuel. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 96 Chapter 4 4.3.4 BMP A204: Mobile Fueling of Vehicles and Heavy Equipment 4.3.4.1 Description of Pollutant Sources Mobile fueling, also known as fleet fueling, wet fueling, or wet hosing, is the practice of filling fuel tanks of vehicles by tank trucks that are driven to the yards or sites where the vehicles to be fueled are located. Mobile fueling is only conducted using diesel fuel, as mobile fueling of gasoline is prohibited. Diesel fuel is considered a Class II Combustible Liquid, whereas gasoline is considered a Flammable Liquid. Historically mobile fueling has been conducted for off-road vehicles that are operated for extended periods of time in remote areas. This includes construction sites, logging operations, and farms. Mobile fueling of on-road vehicles is also conducted commercially in the State of Washington. 4.3.4.2 Pollutant Control Approach Proper training of the fueling operator, and the use of spill/drip control and reliable fuel transfer equipment with backup shutoff valving are typically needed. 4.3.4.3 Required BMPs Organizations and individuals conducting mobile fueling operations must implement the following BMPs. The operating procedures for the driver/operator shall be simple, clear, effective and their implementation verified by the organization that will potentially be liable for environmental and third party damage. • Ensure that all mobile fueling operations are approved and permitted by the Valley Regional Fire Authority and comply with local and Washington State fire codes. Contact the Valley Regional Fire Authority at 253-931-3060. • In fueling locations that are in close proximity to sensitive aquifers, designated wetlands, wetland buffers, or other waters of the State, approval by the City of Auburn is necessary to ensure compliance with additional local requirements. It shall be the responsibility of the site owner to obtain approval under under this exception. Any permit holder permitted under this exception shall cover all catch basins prior to commencing any fueling operations. Sites which are adjacent to designated wetlands, wetland buffers, streams, or bodies of water shall have on site, in a marked conspicuous location a minimum of 50 feet of 4-inch diameter, non-water absorbing containment boom. • Ensure compliance with all 49 CFR 178 requirements for DOT 406 cargo tanker. Documentation from a Department of Transportation (DOT) Registered Inspector shall be proof of compliance. • Ensure the presence and the constant observation/monitoring by the driver/operator at the fuel transfer location at all times during fuel transfer and ensure that the following procedures are implemented at the fuel transfer locations: o Locate the point of fueling at least 25 feet from the nearest storm drain or inside an impervious containment area with a volumetric holding capacity equal to or greater than 110 percent of the receiving tank volume, or place a n S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 97 Chapter 4 impervious covering over the storm drain to ensure no inflow of spilled or leaked fuel. Storm drains that convey the inflow to a spill control separator approved by the City of Auburn and the Valley Regional Fire Authority need not be covered. Potential spill/leak conveyance surfaces must be impervious and in good repair. o Place a drip pan or an absorbent pad under each fueling location prior to and during all dispensing operations. The pan (must be liquid tight) and the absorbent pad must have a capacity of 3 gallons. Spills retained in the drip pan or the pad need not be reported. o Handle and operate fuel transfer hoses and nozzle, drip pan(s), and absorbent pads to prevent spills/leaks of fuel from reaching the ground, storm drains, and receiving waters. o Do not extend the fueling hoses across a traffic lane without fluorescent traffic cones, or equivalent devices. o Remove the fill nozzle and cease filling when the automatic shut-off valve engages. Do not allow automatic shutoff fueling nozzles to be locked in the open position. o Do not “top off” the equipment receiving fuel. • Provide the driver/operator of the fueling vehicle with: o Adequate headlamps, flashlights or other mobile lighting to view fill openings with poor accessibility. Consult with the Valley Regional Fire Authority for additional lighting requirements. o Two-way communication with home base. • Train the driver/operator annually in spill prevention, reporting and cleanup measures and emergency procedures. Make all employees aware of the significant liability associated with fuel spills. • The fueling operation procedures shall be properly signed and dated by the responsible manager, distributed to the operators, retained in the organization files, and made available in the event an authorized government agency requests a review. • Ensure that the Valley Regional Fire Authority (911) and the Ecology Northwest Regional Office (425) 649-7000 are immediately notified in the event of any spill entering surface or groundwaters, including catch basins. Establish a 24-hour “call down list” to ensure the rapid and proper notification of management and government officials should any amount of product be spilled on-site. Keep the list in a protected but readily accessible location in the mobile fueling truck. The “call down list” shall also pre-identify spill response contractors available in the area to ensure the rapid removal of significant product spillage into the environment. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 98 Chapter 4 • Maintain a minimum of the following spill clean-up materials in all fueling vehicles, that are readily available for use: o Non-water absorbents (pads, pillows, sump skimmers) capable of absorbing 15 gallons of diesel fuel; o A storm drain plug or cover kit; o A non-water absorbent containment boom of a minimum 10 feet in length with a 12-gallon absorbent capacity; o A non-metallic shovel; and o Two, five-gallon buckets with lids. o Loose granular absorbent material capable of absorbing a minimum of 5 gallons of diesel. Use only non-water absorbing materials, such as peat moss, during wet weather conditions. • Use automatic shutoff nozzles for dispensing the fuel. Replace automatic shut-off nozzles as recommended by the manufacturer. • Maintain and replace equipment on fueling vehicles, particularly hoses and nozzles, at established intervals to prevent failures. • Do not overfill tanks. Allow room for heat expansion of fuel during warm weather. • Include the following fuel transfer site components: o Automatic fuel transfer shut-off nozzles; and o An adequate lighting system at the filling point. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 4 99 Chapter 4 4.4 Production and Application Activities 4.4.1 BMP A301: Concrete and Asphalt Mixing and Production at Stationary Sites 4.4.1.1 Description of Pollutant Sources This activity applies to businesses and agencies that mix raw materials onsite to produce concrete or asphalt. It also applies to subsequent uses such as pouring concrete structures and making other concrete or asphalt products. Mobile concrete pouring and asphalt application are covered under BMP A302. Requirements for stockpiling of raw materials are covered under BMP A401 Storage or Transfer (Outside) of Solid Raw Materials, By-products or Finished Products. Pollutants of concern include toxic hydrocarbons, toxic organic compounds, oils and greases, heavy metals, and pH. 4.4.1.2 Pollutant Control Approach Cover and contain processes where possible and prevent stormwater run-on and contamination, where feasible. Any facility categorized under SIC Code 2951 or SIC Code 3273 may need to comply with Ecology’s Sand and Gravel General Permit. Contact Ecology at 360-407-6400 for additional information. These facilities may also be subject to City of Auburn requirements. Contact the City of Auburn Public Works Department at 253-931-3010 for further information. 4.4.1.3 Required BMPs The following BMPs or equivalent measures are required of all businesses and public agencies active in concrete and asphalt mixing and production: • Eliminate all illicit connections to the storm drainage system. See BMP S101 for a detailed discussion on identifying and eliminating these connections. • All process water from production, pouring, and equipment cleaning must be discharged to a dead-end sump, a process water treatment system, connected to the sanitary sewer, or recycled. Never wash fresh concrete or concrete mixer washout into streets, storm drainage systems, streams, or other water bodies. • A BMP maintenance schedule must be established, maintenance documented, and employees educated about the need to prevent stormwater contamination through the use and proper maintenance of BMPs. • Production and pouring areas must be protected from stormwater run-on. See BMP S107 for methods of run-on protection. • Cover the production area for prevention of stormwater run-on. See BMP S104 and S107 for information on covers and run-on prevention. • Use absorbent materials or catch basin filters in and around storm drains and catch basins to filter out contaminants. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 00 Chapter 4 4.4.1.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • The production and pouring area should be swept at the end of each work day to collect loose chunks of aggregate and raw materials for recycling or proper disposal. See BMP S102 for disposal options. • Sweep all driveways and gutters that show accumulation of materials to minimize the amount that could be carried offsite by rain and enter the storm drainage system. Use of vacuum sweepers is most efficient. • Asphalt plants should use an oil/water separator to treat stormwater runoff. See Volume V, Water Quality Treatment BMPs, for more information. • Pave the mixing, production, and pouring areas. A sump drain in these areas is probably not advisable due to potential clogging problems, but could be used in a curing area. Sweep these areas to remove remove loose aggregate and recycle or dispose of properly. • Use storm drain covers or similarly effective containment devices to prevent runoff from entering the storm drainage system. Accumulations of dirty runoff must be disposed of properly. Contact the City of Auburn Storm Drainage Utility at 253-931-3010 for information about water quality treatment BMPs for these types of operations. Contact the Department of Ecology’s web page for accepted water quality treatment at http://www.ecy.wa.gov/programs/wq/stormwater/index.html. The use of any treatment BMP must not result in the violation of groundwater, surface water, or wastewater standards. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 01 Chapter 4 4.4.2 BMP A302: Concrete Pouring, Concrete Cutting, and Asphalt Application at Temporary Sites 4.4.2.1 Description of Pollutant Sources This activity applies to businesses and public agencies that apply asphalt or pour or cut concrete for building construction and remodeling, road construction, utility projects, sidewalk, curb and gutter repairs and construction, sealing of driveways and roofs, and other applications. These activities are typically done on a temporary site-to-site basis where permanent BMP measures do not apply. Concrete pouring activities can not only severely alter the pH of receiving waters, but slurry from aggregate washing can harden in storm pipes, thus reducing capacity and creating flooding problems. Pollutants of concern include toxic hydrocarbons, toxic organic compounds, oils and greases, heavy metals, suspended solids, and pH. 4.4.2.2 Pollutant Control Approach Train employees on proper procedures, sweep or shovel aggregate chunks, collect accumulated runoff and solids, and wash equipment in designated areas. 4.4.2.3 Required BMPs The following BMPs or equivalent measures are required of all businesses and agencies doing concrete pouring and asphalt application at temporary sites: • Employees must be educated on the pollution hazards of concrete and asphalt application and cutting. • Loose aggregate chunks and dust must be swept or shoveled and collected (not hosed down a storm drain) for recycling or proper disposal at the end of each work day, especially at work sites such as streets, driveways, parking lots, sidewalks, curbs, and gutters where rain can readily pick up the loose material and carry it to the nearest stormwater conveyance. Small amounts of excess concrete, grout, and mortar can be disposed of in the trash. • Storm drain covers or similarly effective containment devices must be placed over all nearby drains at the beginning of each day. Shovel or vacuum slurry and remove from the site. All accumulated runoff and solids must be collected and properly disposed (see BMP S102 for disposal options) at the end of each work day, or more often if necessary. • Exposed aggregate washing, where the top layer of unhardened concrete is hosed or scraped off to leave a rough finish, must be done with a mechanism for containment and collection of the discarded concrete slurry (such as the storm drain covers mentioned above). The easiest way to contain the washwater is to direct the washings to a trench in the ground where the water can percolate into the ground and the solids later covered with soil. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 02 Chapter 4 • Cleaning of concrete application and mixing equipment or concrete vehicles on the work site must be done in a designated area where the rinse water is controlled. The rinse water must either be collected for proper disposal or put into a trench in the ground where the water can percolate away and the solids later covered with soil or recovered and disposed or recycled. The use of any treatment BMP must not result in the violation of groundwater, surface water, or drinking water quality standards. 4.4.2.4 Recommended BMPs The following BMPs are not required but can provide additional pollution prevention: • Avoid the activity when rain is occurring or expected. • If possible, portable asphalt mixing equipment should be covered by an awning, a lean-to, or another simple structure to avoid contact with rain. See BMP S104 for further details on cover structures. • Recycle broken concrete and asphalt. Look under Recycling Services in the Yellow pages of the phone book to find the nearest recycler. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 03 Chapter 4 4.4.3 BMP A303: Manufacturing and Post-Processing of Metal Products 4.4.3.1 Description of Pollutant Sources This activity applies to businesses such as mills, foundries, and fabricators that manufacture or postprocess metal products. A variety of activities such as machining, grinding, soldering, cutting, welding, quenching, cooling, and rinsing may take place. These businesses may be required to obtain a National Pollutant Discharge Elimination System (NPDES) permit from the Department of Ecology or an Industrial Wastewater Discharge Permit from King County-Metro. See Chapter 5 for a discussion of NPDES requirements and contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 to determine if a wastewater discharge permit is necessary. NOTE: Painting, finishing and coating of metal products is covered under BMP A307 Painting, Finishing, and Coating of Vehicles, Boats, Buildings, and Equipment. Pollutants of concern include toxic organic compounds, heavy metals, oils and greases, pH, suspended solids, and biological oxygen demand (BOD). 4.4.3.2 Pollutant Control Approach Cover and contain operations and apply good housekeeping and preventive maintenance practices to prevent the contamination of stormwater. 4.4.3.3 Required BMPs The following BMPs or equivalent measures are required of all businesses engaged in metals manufacturing or post-processing: • Eliminate illicit connections to the storm drainage system. See BMP S101 for detailed information on identifying and eliminating illicit connections. • Process wastewater (including contact cooling water, filter backwash, cooling tower blowdown, etc.) from this activity, and stormwater runoff from activity areas, must discharge to a sanitary sewer, holding tank, or process treatment system that would need an Ecology NPDES Permit for discharge to surface water or storm drain. Contact the City of Auburn Permit Center at 253-931-3090 to obtain permits for discharge to the sewer. See BMP S103 for detailed requirements. • Employees must be educated to control their work with metal products to minimize pollution. • The activity area must be swept at the end of each work day to collect and dispose of metal fragments and product residues properly. See BMP S102 for disposal alternatives. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 04 Chapter 4 4.4.3.4 Recommended BMPs The following BMPs are not required but can provide additional pollution protection: • Limit the amount of water used in quenching and rinsing. Recycle used water where possible. • Cover the activity area to prevent rain from contacting the process and reduce the amount of runoff that has to be detained or treated. • Use a catch basin filter or screen basket insert to capture stray metal particles. • Implement a program to track purchase and consumption of lubricants, solvents, and additives. Check with operating managers for an explanation if consumption increases. Recommend actions if significant equipment leaks or spills are identified. • Utilize any additional BMPs which are applicable for materials storage and maintenance activities in your shop. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 05 Chapter 4 4.4.4 BMP A304: Wood Treatment Areas 4.4.4.1 Description of Pollutant Sources Wood treatment includes both anti-staining and wood preserving using pressure processes or by dipping or spraying. Wood preservatives include creosote, creosote/coal tar, pentachlorophenol, copper naphthenate, arsenic trioxide, malathion, or inorganic arsenicals such as chromated copper arsenate, acid copper chromate, chromate zinc chloride, and fluor-chrome-arsenate-phenol. Antistaining chemical additives include iodo-prophenyl-butyl carbamate, dimethyl sulfoxide, didecyl dimethyl ammonium chloride, sodium azide, 8-quinolinol, copper (II) chelate, sodium orthophenylphenate, 2-(thiocyanomethylthio)-benzothiazole (TCMTB) and methylene bis-(thiocyanate), and zinc naphthenate. Pollutant sources include drips of condensate or preservative after pressurized treatment, product washwater (in the treatment or storage areas), spills and leaks from process equipment and preservative tanks, fugitive emissions from vapors in the process, blowouts and emergency pressure releases, and kick-back from lumber (phenomenon where preservative leaks as it returns to normal pressure). Potential pollutants typically include the wood treating chemicals, BOD, suspended solids, oil and grease, benzene, toluene, ethylbenzene, phenol, chlorophenols, nitrophenols, heavy metals, and PAH, depending on the chemical additive used. 4.4.4.2 Pollutant Control Approach Cover and contain all wood treating areas and prevent all leaching of and stormwater contamination by wood treating chemicals. All wood treating facilities in Washington State are required to be covered under an individual NPDES Permit and may require an Industrial Wastewater Discharge Permit from King County-Metro. 4.4.4.3 Required BMPs The individual NPDES Permit will require the following BMPs at a minimum: • Dedicate equipment that is used for treatment treatment activities to prevent the tracking of treatment chemicals to other areas on the site. • Eliminate non-process traffic on the drip pad. Scrub down non-dedicated lift trucks on the drip pad. • Immediately remove and properly dispose of soils with visible surface contamination (green soil) to prevent the spread of chemicals to groundwater and/or surface water via stormwater runoff. • If any wood is observed to be contributing chemicals to the environment in the treated wood storage area, relocate it on a concrete chemical containment structure until the surface is clean and until it is drip free and surface dry. • Cover and/or enclose, and contain with impervious surfaces, all wood treatment areas. Slope and drain areas around dip tanks, spray booths, retorts, and any other process equipment in a manner that allows return of treatment chemicals to the wood treatment process. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 06 Chapter 4 • Cover storage areas for freshly treated wood to prevent contact of treated wood products with stormwater. Segregate clean stormwater from process water. Ensure that all process water is conveyed to an approved treatment system. • Seal any holes or cracks in the asphalt areas that are subject to wood treatment chemical contamination. • Elevate stored, treated wood products to prevent contact with stormwater run-on and runoff. • Place dipped lumber over the dip tank or on an inclined ramp for a minimum of 30 minutes to allow excess chemical to drip back to the dip tank. • Place treated lumber either from dip tanks or retorts in a covered paved storage area for at least 24 hours before placement in outside storage. Use a longer storage period during cold weather unless the temporary storage building is heated. The wood shall be drip free and surface dry before before it is moved outside. 4.4.4.4 Recommended BMP Consider using preservative chemicals that do not adversely impact receiving surface water and groundwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 07 Chapter 4 4.4.5 BMP A305: Commercial Composting 4.4.5.1 Description of Pollutant Sources Commercial compost facilities operating outside without cover require large areas to decompose wastes and other feedstocks. These facilities should be designed to separate stormwater from leachate (i.e., industrial wastewater) to the greatest extent possible. When stormwater is allowed to contact any active composting areas, including waste receiving and processing areas, it becomes leachate. Pollutants in leachate include nutrients, biochemical oxygen demand (BOD), organics, coliform bacteria, acidic pH, color, and suspended solids. Stormwater at a compost facility consists of runoff from areas at the facility that are not associated with active processing and curing, such as product storage areas, vehicle maintenance areas, and access roads. 4.4.5.2 NPDES Permit Requirements Discharge of leachate from a compost facility will require a State or NPDES permit from Ecology, depending on the disposal method chosen for managing leachate at the facility (see the Ecology website www.ecy.wa.gov/programs/swfa/compost ). An additional alternative, zero discharge, is possible by containing all leachate from the facility (in tanks or ponds) or preventing production of leachate (by composting under a roof or in an enclosed building). 4.4.5.3 Pollutant Control Approach Consider the leachate control specified on the Ecology website: www.ecy.wa.gov/programs/swfa/compost or zero discharge of leachate. 4.4.5.4 Required BMPs • Ensure that the compost feedstocks do not contain dangerous wastes regulated under Chapter 173-303 WAC or hazardous products of a similar nature or solid wastes that are not beneficial to the composting process. Employees must be trained to screen these materials in incoming wastes. • Contact other federal, state, and City of Auburn departments with environmental or zoning authority for applicable permit and regulatory information. County Health Departments are responsible for issuing solid waste handling permits for commercial compost facilities. • Apply for coverage under the General Permit to Discharge Stormwater Associated with Industrial Activities if the facility discharges stormwater to surface water or a municipal stormwater system. If all stormwater from the facility infiltrates into the surrounding area, the General Permit is not required. • Develop a plan of operations as outlined in the Composting Facility Standards (WAC 173-350-220). • Store finished compost in a manner to prevent contamination of stormwater. • Compost pads are required for all uncovered facilities in areas of the state with wet climates (per water quality regulations). • Provide curbing for all compost pads to prevent stormwater run-on and leachate run-off. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 08 Chapter 4 • Slope all compost pads sufficiently to direct leachate to the collection device. • Provide one or more sumps or catch basins capable of collecting all leachate generated by the design storm and conveying it to the leachate holding structure for all compost pads. • Convey all leachate from composting operations to a sanitary sewer, holding tank, or on-site treatment system designed to treat the leachate. Discharge of leachate to the sanitary sewer may require an Industrial Wastewater Discharge Permit. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for a determination. • Ponds used to collect, store, or treat leachate and other contaminated waters associated with the composting process must be lined to prevent groundwater contamination. Apply “AKART” or All Known Available and Reasonable Methods of Prevention and Treatment to all pond liners, regardless of the construction materials. Refer to “Compost Facility Resource Handbook, Guidance for Washington State,” November 1998, Publication # 97-502, for additional design criteria and information. 4.4.5.5 Recommended BMPs • Clean up debris from yard areas regularly. • Locate stored residues in areas designed to collect leachate. • Limit storage times of residues to prevent degradation and generation of leachate. • Consider using leachate as make-up water in early stages of the composting process. Since leachate can contain pathogenic bacteria, care should be taken to avoid contaminating finished product or nearly finished product with leachate. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 09 Chapter 4 4.4.6 BMP A306: Landscaping and Lawn/Vegetation Management 4.4.6.1 Description of Pollutant Sources Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer application, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with chemical pesticides and is conducted commercially at commercial, industrial, and residential sites. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks; and residential lawn/plant care. Toxic pesticides such as pentachlorophenol, carbamates, and organometallics can be released to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation, poor application of pesticides or fertilizers, and non-targeted irrigation water or over watering can cause appreciable stormwater contamination. 4.4.6.2 Pollutant Control Approach Control of fertilizer and pesticide applications, soil erosion, and site debris to prevent contamination of stormwater. Develop and implement an Integrated Pest Management Plan (IPM) and use pesticides only as a last resort. Refer to Volume IV, Appendix C – Example of an Integrated Pest Management Program for more information. If pesticides/herbicides are used they must be carefully applied in accordance with label instructions on U.S. Environmental Protection Agency (EPA) registered materials. Maintain appropriate vegetation, with proper fertilizer application where practicable, to control erosion and the discharge of stormwater pollutants. Where practicable, grow plant species appropriate for the site, or adjust the soil properties of the subject site to grow desired plant species. 4.4.6.3 Required BMPs for Landscaping • Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. • Do not dispose of collected vegetation into wetlands, waterways or storm drainage systems. 4.4.6.4 Recommended BMPs for Landscaping • Conduct mulch-mowing whenever practicable. • Dispose of grass clippings, leaves, sticks, or other collected vegetation by composting, if feasible. • Collect all clippings, leaves, bark, and trimmings blown onto the sidewalk or street. Do not leave this material in the gutter or where it can be washed into the storm drainage system. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 10 Chapter 4 • Use mulch or other erosion control measures when soils are exposed for more than one week during the dry season or two days during the rainy season. • If oil or other chemicals are handled, store and maintain appropriate oil and chemical spill cleanup materials in readily accessible locations. Ensure that employees are familiar with proper spill cleanup procedures. • Till fertilizers into the soil rather than dumping or broadcasting onto the surface. Determine the proper fertilizer application for the types of soil and vegetation encountered. • Till a topsoil mix or composted organic material into the soil to create a well-mixed transition layer that encourages deeper root systems and drought-resistant plants. • Use manual and/or mechanical methods of vegetation removal rather than applying herbicides, where practical. • Target irrigation water on vegetated vegetated areas and limit irrigation time to reduce the potential of carrying fertilizers and pesticides off-site. 4.4.6.5 Required BMPs for the Use of Pesticides • Develop and implement an integrated pest management system (IPM) (See section on IPM at end of BMP) and use pesticides only as a last resort. • Implement a pesticide-use plan and include at a minimum: a list of selected pesticides and their specific uses; brands, formulations, application methods, and quantities to be used; equipment use and maintenance procedures; safety, storage, and disposal methods; and monitoring, record keeping, and public notice procedures. All procedures shall conform to the requirements of Chapter 17.21 RCW and Chapter 16-228 WAC (Appendix 4 – D.R.7). • Choose the least toxic pesticide available that is capable of reducing the infestation to acceptable levels. The pesticide should readily degrade in the environment and/or have properties that strongly bind it to the soil. Any pest control used should be conducted at the the life stage when the pest is most vulnerable. Any method used should be site-specific and not used wholesale over a wide area. • Apply the pesticide according to label directions. Under no conditions shall pesticides be applied in quantities that exceed manufacturer’s instructions. • Mix the pesticides and clean the application equipment in an area where accidental spills will not enter surface or groundwaters, and will not contaminate the soil. • Store pesticides in enclosed areas or in covered impervious containment. Ensure that pesticide contaminated stormwater or spills/leaks of pesticides are not discharged to storm drains. Do not hose down paved areas to a storm drain or conveyance ditch. Store and maintain appropriate spill cleanup materials in a location known to all near the storage area. • Clean up any spilled pesticides and ensure that the pesticide contaminated waste materials are kept in designated covered and contained areas. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 11 Chapter 4 • The pesticide application equipment must be capable of immediate shutoff in the event of an emergency. • Do not spray pesticides within 100 feet of open waters including wetlands; ponds; and streams, sloughs, and any drainage ditch or channel that leads to open water, except when approved by Ecology or by the City of Auburn. All sensitive areas including wells, creeks, and wetlands must be flagged prior to spraying. • As required by the City of Auburn or by Ecology, complete public posting of the area to be sprayed prior to the application. • Spray applications should only be conducted during weather conditions as specified in the label direction and applicable local and state regulations. Do not apply during rain or immediately before expected rain. 4.4.6.6 Recommended BMPs for the use of Pesticides • Consider alternatives to the use of pesticides such as covering or harvesting weeds, substitute vegetative growth, and manual weed control/moss removal. • Consider the use of soil amendments, such as compost, that are known to control some common diseases in plants, such as Pythium root rot, ashy stem blight, and parasitic nematodes. The following are three possible mechanisms for disease control by compost addition (USEPA Publication 530-F-9-044): o Successful competition for nutrients by antibiotic production; o Successful predation against pathogens by beneficial microorganism; and o Activation of disease-resistant genes in plants by composts. Installing an amended soil/landscape system can preserve both the plant system and the soil system more effectively. This type of approach provides a soil/landscape system with adequate depth, permeability, and organic matter to sustain itself and continue working as an effective stormwater infiltration system and a sustainable nutrient cycle. • Once a pesticide is applied, its effectiveness should be evaluated for possible improvement. Records should be kept showing the applicability and inapplicability of the pesticides considered. • An annual evaluation procedure should be developed including a review of the effectiveness of pesticide applications, impact on buffers and sensitive areas (including potable wells), public concerns, and recent toxicological information on pesticides used/proposed for use. If individual or public potable wells are located in the proximity of commercial pesticide applications, contact the regional Ecology hydrologist to determine if additional pesticide application control measures are necessary. • Rinsate from equipment cleaning and/or triple-rinsing of pesticide containers should be used as product or recycled into product. For more information, contact the WSU Extension Home-Assist Program at 253-445-4556; Bio-Integral Resource Center (BIRC), P.O. Box 7414, Berkeley, CA 94707; or the Washington Department of Ecology to obtain “Hazardous Waste Pesticides” (Publication #89-41); contact EPA to S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 12 Chapter 4 obtain a publication entitled “Suspended, Canceled and Restricted Pesticides” which lists all restricted pesticides and the specific uses that are allowed. Valuable information from these sources may also be available on the internet. 4.4.6.7 Required BMPs for Vegetation Management • Use at least an eight-inch topsoil layer with at least 8 percent organic matter to provide a sufficient vegetation–growing medium. • Select the appropriate turf grass mixture for climate and soil type based on recommendations from a licensed landscape architect. • Selection of desired plant species can be made by adjusting the soil properties of the subject site. For example, a constructed wetland can be designed to resist the invasion of reed canary grass by layering specific strata of organic matters (e.g., compost forest product residuals) and creating a mildly acidic pH and carbon-rich soil medium. Consult a soil restoration specialist for site-specific conditions. • Aerate lawns regularly in areas of heavy use, where the soil tends to become compacted. Aeration shall be conducted while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than ¾-inch deep. • Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. 4.4.6.8 Fertilizer Management: • Fertilization needs vary by site depending on plant, soil, and climatic conditions. Evaluation of soil nutrient levels through regular testing ensures the best possible efficiency and economy of fertilization. For details on soils testing, contact the Pierce Conservation District or Cooperative Extension Service. • Fertilizers shall be applied in amounts appropriate for the target vegetation and at the time of year that minimizes losses to surface and groundwaters. Do not fertilize during a drought or when the soil is dry. Alternatively, do not apply fertilizers within three days prior to predicted rainfall. The longer the period between fertilizer application and either rainfall or irrigation, the less fertilizer runoff occurs. • Use slow release fertilizers such as methylene urea, IDBU, or resin coated fertilizers when appropriate, generally in the spring. Use of slow release fertilizers is especially important in areas with sandy or gravelly soils. • Time the fertilizer application to periods of maximum plant uptake. Generally fall and spring applications are recommended. • Properly trained persons shall apply all fertilizers. Fertilizers shall not be applied to grass swales, filter strips, or buffer areas that drain to surface water bodies. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 13 Chapter 4 4.4.6.9 Integrated Pest Management An IPM program might consist of the following steps: 1. Correctly identify problem pests and understand their life cycle. 2. Establish tolerance thresholds for pests. 3. Monitor to detect and prevent pest problems. 4. Modify the maintenance program to promote healthy plants and discourage pests. 5. Use cultural, physical, mechanical, or biological controls first if pests exceed the tolerance thresholds. 6. Evaluate and record the effectiveness of the control and modify maintenance practices to support lawn or landscape recovery and prevent recurrence. For an elaboration of these steps refer to Volume IV, Appendix C – Example of an Integrated Pest Management Program. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 14 Chapter 4 4.4.7 BMP A307: Painting, Finishing and Coating of Vehicles, Boats, Buildings and Equipment 4.4.7.1 Description of Pollutant Sources Surface preparation and the application of paints, finishes, and/or coatings to vehicles, boats, buildings, and/or equipment outdoors can be sources of pollutants. Potential pollutants include organic compounds, oils and greases, heavy metals, and suspended solids. 4.4.7.2 Pollutant Control Approach Cover and contain painting and sanding operations and apply good housekeeping and preventive maintenance practices to prevent the contamination of stormwater with painting overspray and grit from sanding. 4.4.7.3 Required BMPs • Train employees in the careful application of paints, finishes, and coatings to reduce misuse and over spray. Use ground or drop cloths or temporary berms underneath outdoor painting, scraping, sandblasting work, and properly clean and temporarily store collected debris daily. • Do not conduct spraying, blasting, or sanding activities over open water or where wind may blow paint into water. • Wipe up spills with rags and other absorbent materials immediately. Do not hose down the area to a storm drain, receiving water, or conveyance ditch to receiving water. • On dock areas, sweep or vacuum rather than hose down debris. Collect any hose water generated and convey to appropriate treatment and disposal. • Use a storm drain cover, filter fabric, or similarly effective runoff control device if dust, grit, washwater, or other pollutants may escape the work area and enter a catch basin. The containment device(s) must be in place at the beginning of the workday. Collect contaminated runoff and solids and properly dispose of such wastes before removing the containment device(s) at the end of the workday. • Use a ground cloth, pail, drum, drip pan, tarpaulin, or other protective device (e.g. plastic wading pool) for activities such as paint mixing and tool cleaning outside or where spills can contaminate stormwater. • Properly dispose of all wastes and prevent all uncontrolled releases to the air, ground, or water. • Clean brushes and tools covered with non-water-based paints, finishes, or other materials in a manner that allows collection of used solvents (e.g., paint thinner, turpentine, xylol, etc.) for recycling or proper disposal. • Store toxic materials under cover (tarp, etc.) during precipitation events and when not in use to prevent contact with stormwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 15 Chapter 4 • Enclose and/or contain all work while using a spray gun or conducting sand blasting and in compliance with applicable air pollution control, OSHA, and WISHA requirements. Do not conduct outside spraying, grit blasting, or sanding activities during windy conditions which render containment ineffective. 4.4.7.4 Recommended BMPs • Clean paintbrushes and tools covered with water-based paints in sinks connected to sanitary sewers or in portable containers that can be dumped into a sanitary sewer drain. • Recycle paint, paint thinner, solvents, pressure wash water, and any other recyclable materials. • Use efficient spray equipment such as electrostatic, air-atomized, high volume/low pressure, or gravity feed spray equipment. • Purchase recycled paints, paint thinner, solvents, and other products if feasible. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 16 Chapter 4 4.4.8 BMP A308: Commercial Printing Operations 4.4.8.1 Description of Pollutant Sources Materials used in the printing process include inorganic and organic acids, resins, solvents, polyester film, developers, alcohol, vinyl lacquer, dyes, acetates, and polymers. Waste products may include waste inks and ink sludge, resins, photographic chemicals, solvents, acid and alkaline solutions, chlorides, chromium, zinc, lead, spent formaldehyde, silver, plasticizers, and used lubricating oils. As the printing operations are conducted indoors, the only likely points of potential contact with stormwater are the outside temporary waste material storage area and area where chemicals are offloaded at external unloading bays. Pollutants can include TSS, pH, heavy metals, oil and grease, and COD. 4.4.8.2 Pollutant Control Approach Ensure appropriate disposal and NPDES permitting of process wastes. Cover and contain stored raw and waste materials. 4.4.8.3 Required BMPs • Discharge process wastewaters to a sanitary sewer (if approved by the City of Auburn) or to an approved process wastewater treatment system. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for discharge requirements. • Do not discharge process wastes or wastewaters into storm drains or surface water. • Determine whether any of these wastes qualify for regulation as dangerous wastes and dispose of them accordingly. • Store raw materials or waste materials that could contaminate stormwater in covered and contained areas. 4.4.8.4 Recommended BMPs • Train all employees in pollution prevention, spill response, spill reporting, and environmentally acceptable materials handling procedures. • Store materials in proper, appropriately labeled containers. Identify and label all chemical substances. • All stormwater management devices should be inspected regularly and maintained as necessary. • Try to use use press washes without listed solvents, and with the lowest VOC content possible. Do not evaporate ink cleanup trays to the outside atmosphere. • Place cleanup sludges into a properly labeled container with a tight lid and dispose of as hazardous waste. Do not dispose of cleanup sludges in the garbage or in containers of soiled towels. For additional information on pollution prevention the following Washington Department of Ecology publications are recommended: A Guide for Screen Printers, Publication #94-137 and A Guide for Lithographic Printers, Publication #94-139. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 17 Chapter 4 4.4.9 BMP A309: Manufacturing Operations – Outside 4.4.9.1 Description of Pollutant Sources Manufacturing pollutant sources include outside process areas, stack emissions, and areas where manufacturing activity has taken place in the past and significant pollutant materials remain and are exposed to stormwater. 4.4.9.2 Pollution Control Approach Cover and contain outside manufacturing and prevent stormwater run-on and contamination, where feasible. 4.4.9.3 Required BMPs • Sweep paved areas regularly, as needed, to prevent contamination of stormwater. Vacuum sweeping is preferred. • Alter the activity by eliminating or minimizing the contamination of stormwater. • Enclose the activity (see Figure IV-4-9). If possible, enclose the manufacturing activity in a building. • Cover the activity and connect floor drains to a sanitary sewer, if approved by the City of Auburn. Berm or slope the floor as needed to prevent drainage of pollutants to areas outside (see Figure IV-4-10). • Isolate and segregate pollutants, as feasible. Convey the segregated pollutants to a sanitary sewer, process treatment, or dead-end sump, depending on available methods and applicable permit requirements. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 18 Chapter 4 Figure 4.7 – Enclose the Activity Figure IV-4-9. Enclose the Activity Figure 4.8 – Cover the Activity Figure IV-4-10. Cover the Activity S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 19 Chapter 4 4.5 Storage and Stockpiling Activities 4.5.1 BMP A401: Storage or Transfer (Outside) of Solid Raw Materials, By-Products or Finished Products 4.5.1.1 Description of Pollutant Sources Solid raw materials, by-products, or products such as gravel, sand, salts, topsoil, compost, logs, sawdust, wood chips, lumber and other building materials, concrete, and metal products are typically stored outside in large piles, stacks, etc. at commercial or industrial establishments. Contact of outside bulk materials with stormwater can cause leachate and/or erosion of the stored materials. Contaminants may include TSS, BOD, organics, and dissolved salts (sodium, calcium, magnesium chloride, etc). 4.5.1.2 Pollutant Control Approach Provide impervious containment with berms, dikes, etc. and/or cover to prevent run-on and discharge of leachate, pollutant(s) and TSS. 4.5.1.3 Required BMPs • Do not hose down the contained stockpile area to a storm drain or other conveyance leading to a storm drain or receiving water. • Choose one or more of the source control BMP options listed below for stockpiles greater than 5 cubic yards of erodible or water soluble materials such as soil, road deicing salts, compost, unwashed sand and gravel, sawdust, etc. or for outside storage areas for solid materials such as logs, bark, lumber, metal products, etc.: o Store in a building or paved and bermed covered area as shown in Figure IV-4-11. o Place temporary plastic sheeting (polyethylene, polypropylene, hypalon, or equivalent) over the material as shown in Figure IV-4-12. OR o Pave the area and install a stormwater drainage system. Place curbs or berms along the perimeter of the area to prevent the run-on of uncontaminated stormwater and to collect and convey runoff to treatment. Slope the paved area in a manner that minimizes contact between stormwater (e.g., pooling) and leachable materials in compost, logs, bark, wood chips, etc. o For large stockpiles that cannot be covered, implement containment practices at the perimeter of the site and at any catch basins as needed to prevent erosion and discharge of the stockpiled material offsite or to a storm drain. Ensure that contaminated stormwater is not discharged directly to catch basins without being conveyed through a treatment BMP. For log yards see Ecology publication “Industrial Stormwater General Permit Implementation Manual for Log Yards:, publication # 04-10-031. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 20 Chapter 4 o Convey contaminated stormwater from the stockpile area to a wet pond, wet vault, settling basin, media filter, or other appropriate treatment system, depending on the contaminate. Figure IV-4-11. Covered Storage Area for Bulk Solids (including berm if needed) 4.5.1.4 Recommended BMPs • Maintain drainage areas in and around storage of solid materials with a minimum slope of 1.5 percent to prevent pooling and minimize leachate formation. Areas should be sloped to drain stormwater to the perimeter where it can be collected, or to internal drainage “alleyways” where material is not stockpiled. • Sweep paved storage areas regularly for collection and disposal of loose solid materials. • If and when feasible, collect and recycle water-soluble materials (leachates) to the stockpile. • Stock cleanup materials such as brooms, dustpans, and vacuum sweepers near the storage area. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 21 Chapter 4 Figure IV-4-12. Material Covered with Plastic Sheeting S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 22 Chapter 4 4.5.2 BMP A402: Storage and Treatment of Contaminated Soils 4.5.2.1 Description of Pollutant Sources This activity applies to businesses and agencies that store and treat soils contaminated with toxic organic compounds, petroleum products, or heavy metals. Stormwater runoff that comes in contact with contaminated soil can carry those contaminants along with loose dirt into receiving waters. 4.5.2.2 Pollutant Control Approach Ecology regulates businesses disposing and treating contaminated soil. A permit from the Puget Sound Clean Air Agency is required if the treatment method for removing soil contaminants involves forcing air through, or sucking air from, the soil. In addition, a Special Approved Discharge Authorization from the Metro-King County may be required if potentially contaminated water is to be discharged from the site. The Puget Sound Clean Air Agency can be reached at 1-800-552-3565. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010. 4.5.2.3 Required BMPs The BMPs included here are intended as a supplement to other regulations. The following BMPs or equivalent measures are required of all businesses engaged in storage and treatment of contaminated soils: • The storage area for contaminated soils must be enclosed indoors, covered, or contained by a curb, dike, or berm constructed around the material storage area. If the contaminated soils are covered, stormwater run-on protection must also be provided. BMP S107 provides further details on containment and run-on prevention. • Employees must be educated on methods to prevent contamination from leaving the site. • Cleanup materials must be stocked near the storage area. • Gutters, storm drains, catch basins, and other drainage system features on the site must be cleaned following the completion of site work, or at least once per year, whichever comes first. Sediments from such cleaning must be disposed of properly. See BMP S109 and S102 for details on catch basin cleaning and disposal options. 4.5.2.4 Recommended BMPs The following BMPs are not required but can provide additional pollution protection: • If feasible, the storage area should be swept weekly for collection of stray soil, which can be added back to the piles or properly disposed. See BMP S102 for information on disposal options. • Implement one of the following treatment BMPs in conjunction with a runoff containment plan: o Vegetated biofilter. o Equivalent BMP for the targeted pollutant (see Volume V). The use of any treatment BMP must not result in the violation of groundwater, surface water, wastewater, or drinking water quality standards. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 23 Chapter 4 4.5.3 BMP A403: Temporary Storage or Processing of Fruits or Vegetables 4.5.3.1 Description of Pollutant Sources This activity applies to businesses that temporarily store fruits and vegetables outdoors prior to processing or sale, or that crush, cut, or shred fruits or vegetables for wines, frozen juices, and other food and beverage products. These businesses may include farmers markets, fruit and vegetable stands, and fruit and vegetable processors. Nutrients and soil washing off of fruit and vegetables can have a detrimental effect on receiving waters. Pollutants of concern include nutrients, suspended solids, biochemical oxygen demand (BOD), and color. 4.5.3.2 Pollutant Control Approach Store and process fruits and vegetables indoors or under cover whenever possible. Educate employees about proper procedures. Eliminate illicit connections to the storm drainage system. Cover and contain operations and apply good housekeeping and preventive maintenance practices to prevent the contamination of stormwater. 4.5.3.3 Required BMPs The following BMPs or equivalent measures are required of all businesses engaged in storage of fruits or vegetables: • Employees must be educated on benefits of keeping a clean storage area. • Eliminate illicit connections to the storm drainage system. See BMP S101 for details on detecting and eliminating these connections. • Water used to clean produce or other liquid wastes cannot enter the storm drainage system unless treated. Minimize the use of water when cleaning produce to avoid excess runoff. • Cleanup materials, such as brooms and dustpans, must be kept near the storage area. • Gutters, storm drains, and catch basins on the property must be cleaned as needed. See BMP S109 for details on catch basin cleaning requirements. The following BMPs or equivalent measures are required of all businesses that process fruits or vegetables: • • Eliminate illicit connections to the storm drainage system. See BMP S101 for details on detecting and eliminating these connections. • Employees must be educated on benefits of keeping a clean processing area. • Cleanup materials, such as brooms, dustpans, and shovels, must be kept near the storage area. • The processing area must be swept or shoveled daily to collect dirt and fruit and vegetable fragments for proper disposal. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 24 Chapter 4 • The processing area must be enclosed in a building or shed, or covered with provisions for stormwater run-on prevention. See BMP S104, S105, and S107 for more on covering and run-on prevention. OR The processing area must be paved and sloped to a sanitary sewer drain, holding tank, or process treatment system collection drain, and stormwater run-on prevention must be provided for the processing area. Call the Auburn Permit Center at 253-931-3090 for information on discharging to the sanitary sewer. See BMP S106 and S103 for details on paving and drainage. 4.5.3.4 Recommended BMPs The following BMPs are not required but can provide additional pollution protection: • Cover storage areas for fruits and vegetables. See BMP S104 and S105 for more details on coverings. • A containment curb, dike, or berm can be used to prevent offsite runoff from storage or processing areas and also to prevent stormwater run-on. See BMP S107 for more information. Note that run-on prevention is required for processing areas, but not for storage areas. • The storage area should be swept or shoveled daily to collect dirt and fruit and vegetable fragments for proper disposal. Keep hosing to a minimum. • Use one or a combination of the following treatment BMPs: o Wet pond or wet vault to treat storage area runoff. o Vegetated biofilter to treat storage area runoff. o Catch basin with appropriate insert for the targeted pollutants to treat storage area runoff. See S109 for information on catch basin cleaning. o Equivalent BMP (see Volume V). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 25 Chapter 4 4.5.4 BMP A404: Storage of Solid Wastes and Food Wastes 4.5.4.1 Description of Pollutant Sources This activity applies to facilities such as hospitals, restaurants, meat and seafood markets, veterinarian clinics, schools, grocery stores, assisted living centers, and group assembly halls that store solid wastes and food wastes outdoors. This includes ordinary garbage. If improperly stored, these wastes can contribute a variety of different pollutants to stormwater. Requirements for handling and storing solid waste may include a permit from the local health departments; Tacoma-Pierce County Health Department or Seattle-King County Health Department NOTE: Dangerous solid wastes must be stored and handled under special guidelines. Businesses and agencies that store dangerous wastes must follow specific regulations outlined by the Department of Ecology. Ecology regulations are outlined in Volume IV, Chapter 5. Please contact the Department of Ecology at 360-407-6300 for the specific requirements and permitting information. Pollutants of concern include toxic organic compounds, oils and greases, heavy metals, nutrients, suspended solids, chemical oxygen demand (COD), and biochemical oxygen demand (BOD). 4.5.4.2 Pollutant Control Approach Store wastes in suitable containers with leak-proof lids. Sweep or shovel loose solids. Educate employees about the need to check for and replace leaking containers. 4.5.4.3 Required BMPs The following BMPs are required of all businesses and public agencies engaged in storage of nondangerous solid wastes or food wastes: • All solid and food wastes must be stored in suitable containers. Piling of wastes without any cover is prohibited. • Waste storage areas and trash enclosures for food or liquid bearing wastes must be connected to the sanitary sewer and bermed or sloped to prevent stormwater run-on. • Trash compactors or dumpsters for for food or liquid-bearing wastes shall drain to the sanitary sewer system and be designed as required by the City of Auburn. • Storage containers must be checked for leaks and replaced if they are leaking, corroded, or otherwise deteriorating. If storage containers contain liquid wastes of any kind, then the container shall be located on a pad equipped with a drainage system connected to the City sanitary sewer. • Storage containers must have leak-proof lids or be covered by some other means. Lids must be kept closed at all times. This is especially important for dumpsters, as birds can pick out garbage and drop it, promoting rodent, health, and stormwater problems. OR • If lids cannot be provided for the waste containers, or they cannot otherwise be covered, there is another option: a designated waste storage area must be provided S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 26 Chapter 4 with a containment berm, dike, or curb, and the designated area must drain to a sanitary sewer or holding tank for further treatment. See BMP S107 and S103 for more information. • Do not completely fill containers of waste grease and oil. Leave a minimum of four inches of freeboard to prevent spills when the containers are moved or handled for recycling. • Employees must be trained to check storage containers frequently for leaks and to ensure that the lids are on tightly. • The waste storage area must be swept or otherwise cleaned frequently to collect all loose solids for proper disposal in a storage container. Do not hose the area to collect or clean solids. • If containers are cleaned, all rinse water from cleaning must be disposed of in a sanitary sewer or septic system. • Inspect regularly and clean out catch basins on the property that receive drainage drainage from waste storage area. See BMP S109 for details on catch basin cleaning. 4.5.4.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • If the amount of waste accumulated appears to frequently exceed the capacity of the storage container, then another storage container should be obtained and utilized. • Store containers such that wind will not be able to knock them over. • Designate a storage area, pave the area, and slope the drainage to a holding tank or sanitary sewer drain. If a holding tank is used, the contents must be pumped out before the tank is full and properly disposed. See BMP S102 for more information on disposal options. • Compost appropriate wastes. Contact Auburn Solid Waste and Recycling Utility Recycling at 253-931-3038 for more information on composting. • Recycle solid wastes. The Industrial Materials Exchange (IMEX) program facilitates the transfer of excess materials and wastes to those who can use them. IMEX can be reached at 206-296-4899, or use the IMEX computer bulletin board modem access number at 1-800-858-6625. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 27 Chapter 4 4.5.5 BMP A405: Recyclers and Scrap Yards 4.5.5.1 Description of Pollutant Sources Includes businesses that reclaim various materials for resale or for scrap, such as vehicles and vehicle/equipment parts, construction materials, metals, computers, appliances, beverage containers, and papers. Potential sources of pollutants include paper, plastic, metal scrap debris, engines, transmissions, radiators, batteries, and other materials that contain fluids or are contaminated with fluids. Other pollutant sources include leachate from metal components, contaminated soil, and the erosion of soil. Activities that can generate pollutants include the transfer, dismantling, and crushing of vehicles and scrap metal; the transfer and removal of fluids; maintenance and cleaning of vehicles, parts, and equipment; and storage of fluids, parts for resale, solid wastes, scrap parts, and materials, equipment and vehicles that contain fluids, generally in uncovered areas. Potential pollutants typically found at vehicle recycle and scrap yards include oil and grease, ethylene and propylene glycol, total suspended solids, BOD, heavy metals, and acidic pH. 4.5.5.2 Required BMPs For facilities subject to Ecology’s Industrial Stormwater General Permit refer to BMP Guidance Document #94-146, “Vehicle Recyclers: A Guide to Implementing the Industrial Stormwater General National Pollutant Discharge Elimination System (NPDES) Permit Requirements”, Washington Department of Ecology, January 2006 for selection of BMPs. The BMPs in that guidance document can also be applied to scrap material recycling facilities (depending on the pollutant sources existing at those facilities) and to non-permitted facilities. Contact the City of Auburn Public Works Department at 253-931-3010 if contact stormwater or process wastewater is to be discharged from your site. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 28 Chapter 4 4.5.6 BMP A406: Treatment, Storage or Disposal of Dangerous Wastes This activity applies to businesses and public agencies that are permitted by the Washington State Department of Ecology (DOE) to treat, store, or dispose of dangerous wastes. DOE regulates these facilities with specific requirements, which include the need for a National Pollutant Discharge Elimination System (NPDES) permit. Detailed BMPs are not included in this manual since site requirements for these facilities are well beyond the level of typical BMP applications. See Chapter 5 of this volume for reference information. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 for their requirements. An Industrial Wastewater Discharge Permit is required before discharging contact stormwater or process wastewater to the municipal sewer system. The Department of Ecology regulates the the treatment, storage and disposal of Dangerous Wastes. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 29 Chapter 4 4.5.7 BMP A407: Storage of Liquid, Food Waste or Dangerous Waste Containers 4.5.7.1 Description of Pollutant Sources Steel and plastic drums with volumetric capacities of 55 gallons or less are typically used at industrial facilities for storage of liquids and powders. The BMPs specified below apply to container(s) located outside a building used for temporary storage of accumulated food wastes, vegetable or animal grease, used oil, liquid feedstock cleaning chemicals, or Dangerous Wastes (liquid or solid), unless the business is permitted by Ecology to store the wastes. Leaks and spills of pollutant materials during handling and storage are the primary sources of pollutants. Oil and grease, acid/alkali pH, BOD, and metals are potential pollutant constituents. 4.5.7.2 Pollutant Control Approach Store containers in impervious containment under a roof or other appropriate cover, or in a building. For roll-containers (for example, dumpsters) that are picked up directly by the collection truck, a filet can be placed on both sides of the curb to facilitate moving the dumpster. If a storage area is to be used on-site for less than 30 days, a portable temporary secondary system like that shown in Figure IV-4-13 can be used in lieu of a permanent system as described above. 4.5.7.3 Required BMPs • Place tight-fitting lids on all containers. Provide adequate freeboard/headspace. • Place drip pans beneath all mounted container taps and at all potential drip and spill locations during filling and unloading of containers. • Inspect container storage areas regularly for corrosion, structural failure, spills, leaks, overfills, and failure of piping systems. Check containers daily for leaks/spills. Replace containers, secure lids, and replace and tighten bungs in drums, as needed. • Drums stored in an area where unauthorized persons may gain access must be secured in a manner that prevents accidental spillage, pilferage, or any unauthorized use (see Figure IV-4-14). • If the material is a Dangerous Waste, the business owner must comply with any additional Ecology requirements as specified in Chapter 5. • Storage of reactive, ignitable, or flammable liquids must comply with the Uniform Fire Code. • Cover dumpsters or keep them under cover, such as a lean-to, to prevent the entry of stormwater. Replace or repair leaking garbage dumpsters. • Drain dumpsters and/or dumpster pads to sanitary sewer. Keep dumpster lids closed. Install waterproof liners. • Keep containers with Dangerous Waste, food waste or other potential pollutant liquids inside a building unless this is impracticable due to site constraints or Uniform Fire Code requirements. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 30 Chapter 4 • Store containers in a designated area that is covered, bermed, or diked; paved; and impervious in order to contain leaks and spills (see Figure IV-4-15). The secondary containment shall be sloped to drain into a dead-end sump for the collection of leaks and small spills. • For liquid wastes, surround the containers with a dike as illustrated in Figure IV-4-15. The dike must be of sufficient height to provide a volume of 10 percent of the total enclosed container volume or 110 percent of the volume contained in the largest container, whichever is greater, or, if a single container, 110 percent of the volume of that container. • Where material is temporarily stored in drums, a containment system can be used, as illustrated, in lieu of the above system (see Figure IV-4-13). • Place containers mounted for direct removal of a liquid chemical for use by employees employees inside a containment area as described above. Use a drip pan during liquid transfer (see Figure IV-4-16). • For contaminated stormwater in the containment area, connect the sump outlet to a sanitary sewer, if approved by the City of Auburn, or to appropriate treatment such as an API or CP oil/water separator, catch basin filter, or other appropriate system (see Volume V). Equip the sump outlet with a normally closed and locked steel line and valve to prevent the release of spilled or leaked liquids, especially flammables (in compliance with Fire Codes), and dangerous liquids. This valve may be opened only for the conveyance of contaminated stormwater to treatment. Maintain a log to record inspections and when the containment area is drained to treatment. • Another option for discharge of contaminated stormwater is to provide a dead-end sump or catchment. Stormwater can then be pumped to a tank truck or other appropriate vehicle for off-site treatment and/or disposal. Figure 4.11 – Secondary Containment System Figure IV-4-13. Secondary Containment Vessel S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 31 Chapter 4 Figure 4.12 – Locking System for Drum Lid Figure IV-4-14. Locking System for Drum Lid Figure IV-4-15. Covered and Bermed Containment Area Figure IV-4-16. Mounted Container S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 32 Chapter 4 4.5.8 BMP A408: Storage of Liquids in Above-Ground Tanks 4.5.8.1 Description of Pollutant Sources Above-ground tanks containing liquids (excluding uncontaminated water) may be equipped with a valved drain, vent, pump, and bottom hose connection. These tanks may be heated with steam heat exchangers equipped with steam traps. Leaks and spills can occur at connections and during liquid transfer. Oil and grease, organics, acids, alkalis, and heavy metals in tank water and condensate drainage can also cause stormwater contamination at storage tanks. 4.5.8.2 Pollutant Control Approach Install secondary containment or a double-walled tank. Slope the containment area to a drain with a sump. Stormwater collected in the containment area may need to be discharged to treatment such as an API or CP oil/water separator, or equivalent BMP. Add safeguards against accidental releases including protective guards around tanks to protect against vehicle or forklift damage, and tag valves to reduce human error. Tank water and condensate discharges are process wastewater that may need an NPDES Permit or approval to discharge to the sanitary system. 4.5.8.3 Required BMPs for All Tanks • Inspect the tank containment areas regularly to identify leaks/spills, cracks, corrosion, etc. in problem components such as fittings, pipe connections, and valves. • Develop a spill plan as per the requirements of BMP A714: Spills of Oil and Hazardous Substances. • Place adequately sized drip pans beneath all mounted taps and drip/spill locations during filling/unloading of tanks. Valved drain tubing may be needed in mounted drip pans. • Sweep and clean the tank storage area regularly, if paved. • Replace or repair tanks or other components that are leaking, corroded, or otherwise deteriorating. • All installations shall comply with the International Fire Code and the National Electric Code. • Locate permanent tanks in impervious (Portland cement concrete or equivalent) secondary containment surrounded by dikes as illustrated in Figure IV-4-17, or use UL approved double-walled tanks. • Double-walled tanks with exposure to traffic must be protected with bollards, jersey barriers, or walls. Bollards should be at least 4 feet high, at least 3 feet from the tank, and no more than 4 feet apart. • Include a tank overfill protection system to minimize the risk of spillage during loading. • There must be at least 5 feet of space between the tanks and any enclosures. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 33 Chapter 4 4.5.8.4 Required BMPs for Single-walled Tanks • The containment volume shall be 100% of the volume of the largest tank plus the volume of stormwater from rain events up to a 25-year, 24-hour storm within the containment area or 110% of the volume of the largest tank, whichever is greater. • There must be at least 5 feet of space between the tanks and any enclosures. • Slope the secondary containment to drain to a dead-end sump (optional), or equivalent, for the collection of small spills. • If the tank containment area is uncovered, equip the outlet from the spill-containment sump with a shutoff valve, which is normally closed and locked. Valves for flammables containment shall be made of steel. Valves for corrosives containment shall be compatible with the material being stored. • The external valve may be opened manually only to convey contaminated stormwater to an approved treatment or disposal facility, or to convey uncontaminated stormwater to a storm drain. Evidence of contamination can include the presence of visible sheen, color, or turbidity in the runoff, or existing or historical operational problems at the facility. Simple pH measurements with litmus or pH paper can be used for areas subject to acid or alkaline contamination. • At petroleum tank farms, convey stormwater contaminated with floating oil or debris in the contained area through an API or CP-type oil/water separator (Volume V, Treatment BMPs) or other approved treatment facility prior to discharge to storm drain or surface water. Direct discharges require an NPDES permit from the Department of Ecology. • Loading racks and transfer areas associated with tank farms shall provide spill containment and treatment sized to encompass the largest vessel (trailer, railcar, intermodal tank) using the area. 4.5.8.5 Recommended BMPs for Double-walled Tanks • Tank pads and the fuel delivery area should should be protected from stormwater run-on but sized and sloped to capture any leaks or spills from the tank or fueling process. • Feed and return lines from the tanks shall be doubled walled or entirely contained within the utility corridor. • Catch basins receiving drainage from the tank pad and fueling area should be oversized and have down-turned elbows in their outlets or flow to an appropriately sized oil/water separator. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 34 Chapter 4 Figure IV-4-17. Above-Ground Tank Storage S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 35 Chapter 4 4.5.9 BMP A409: Parking and Storage for Vehicles and Equipment 4.5.9.1 Description of Pollutant Sources Parked vehicles at public and commercial parking lots and garages, such as retail store, fleet vehicle (including rent-a-car lots and car dealerships), equipment sale and rental parking lots, and parking lot driveways, can be sources of toxic hydrocarbons and other organic compounds, oils and greases, metals, and suspended solids. 4.5.9.2 Required BMPs • If washing of a parking lot is conducted, discharge the wash water to a sanitary sewer (if allowed by the City of Auburn) or other approved wastewater treatment system, or collect it for off-site disposal. • Do not hose down the area to a storm drain or receiving water. Sweep (vacuum sweeping is preferred) parking lots, storage areas, and driveways regularly to collect dirt, waste, and debris. • An oil removal system such as an API or CP oil and water separator, catch basin filter, or equivalent BMP (see VV), approved by the City of Auburn, is applicable for parking lots meeting the threshold vehicle traffic intensity level of a high-use site. For more information on high-use sites, refer to Volume V, Chapter 1. • Covered floors of parking garages must drain to the sanitary sewer through an approved oil/water separator. Uncovered floors must be routed to the storm drainage system through an approved treatment device. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 36 Chapter 4 4.6 Construction and Demolition Activities 4.6.1 BMP A501: Clearing, Grading and Preparation of Construction Sites This activity applies to businesses and municipal agencies that develop lands for construction. It also applies to residences that undertake large yard clearing and grading projects. Stormwater runoff from bare ground can be loaded with dirt and other pollutants. This material can clog ditches and stream channels, thus reducing carrying capacity and increasing flooding, as well as smothering spawning beds for fish. Simply controlling runoff and not allowing it to leave the site will prevent these harmful effects. Clearing, grading, and preparation activities are covered in detail in Volume II of this manual, Construction Stormwater Pollution Prevention. Grading activities are also regulated in the City of Auburn by the Grading and Excavation Code, Chapter 15.74 ACC. Control of stormwater run-on and soil stabilization is critical. Limiting the area to be cleared and graded during wet weather seasons will make site stabilization and sediment control easier. Coverage under Ecology’s Construction Stormwater General Permit is required for construction sites that result in the disturbance of one acre or more of land. Compliance with the Construction Stormwater Pollution Prevention requirements in Ecology’s manual is required, as applicable. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 37 Chapter 4 4.6.2 BMP A502: Demolition of Buildings 4.6.2.1 Description of Pollutant Sources This activity applies to removal of existing buildings by controlled explosions, wrecking balls, or manual methods, and subsequent clearing of the rubble. The loose debris can contaminate stormwater. Pollutants of concern include toxic organic compounds, heavy metals, asbestos, and suspended solids. 4.6.2.2 Pollutant Control Approach Regularly clean up debris that can contaminate stormwater. Protect the storm drainage system from dirty runoff and loose particles. Sweep paved surfaces daily. Vacuum sweeping is preferred. 4.6.2.3 Required BMPs The following BMPs or equivalent measures are required of all businesses and public agencies engaged in building demolition: • Identify and properly abandon all utility connections such as sanitary sewer, gas, fuel lines and tanks. • If directed to keep water out of the storm system during demolition activity, storm drain covers or a similarly effective containment device must be placed on all nearby drains to prevent dirty runoff and loose particles from entering the storm drainage system. If storm drains are not present, dikes, berms, or other methods must be used to protect overland discharge paths from runoff. See BMP S102 and S107 for more information on runoff control and disposal options. • Utilize storm drain inlet protection per BMP C220. • Street gutters, sidewalks, driveways, and other paved surfaces in the immediate area of the demolition must be swept at the end of each work day to collect and properly dispose of loose debris and garbage. 4.6.2.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • Water should be sprayed throughout the site to help control wind blowing of fine materials such as soil, concrete dust, and paint chips. The amount of water must be controlled so that runoff from the site does not occur, yet dust control is achieved. Oils must never be used for dust control. • If possible, a wall should be constructed to prevent stray building materials and dust from escaping the area during demolition. • Install catch basin filter inserts to treat site runoff. Additional information about catch basin filter inserts can be found in Volume II, BMP C220. • Schedule demolition to take place at a dry time of the year. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 38 Chapter 4 4.6.3 BMP A503: Building, Repair, Remodeling and Construction 4.6.3.1 Description of Pollutant Sources This activity refers to activities associated with construction of buildings and other structures, remodeling of existing buildings and houses, and general exterior building repair work. Washing of buildings is covered under A103 Washing, Pressure Washing, and Steam Cleaning. Painting of buildings is covered under A307 Painting, Finishing, and Coating of Vehicles, Boats, Buildings, and Equipment. Concrete pouring is covered under A302 Concrete Pouring and Asphalt Application at Temporary Sites. Pollutants of concern include toxic organics, suspended solids, heavy metals, asbestos, pH, oils, and greases. 4.6.3.2 Pollutant Control Approach Employees must be educated about the need to control site activities. Control leaks, spills, and loose material. Utilize good housekeeping practices. 4.6.3.3 Required BMPs The following BMPs or equivalent measures are required of all businesses engaged in building repair, remodeling, and construction: • Employees must be educated about the need to control site activities to prevent stormwater pollution, and also must be trained in spill cleanup procedures. • Spill cleanup materials, appropriate to the chemicals being used on site, must be available at the work site at all times. • The work site must be cleaned up at the end of each work day, with materials such as solvents put away indoors or covered and secured so that vandals will not have access to them. • The area must be swept daily to collect loose litter, paint chips, grit, and dirt. • Absolutely no substance can be dumped on pavement, the ground, or in or toward storm drains, regardless of its content, unless it is only uncontaminated water. • Bermed ground or drop cloths must be used underneath scraping and sandblasting work. Ground cloths, buckets, or tubs must also be used anywhere that work materials are laid down. • Tools covered with non-water-based finishes or other materials must be cleaned in a manner that enables collection of used solvents for recycling or proper disposal. See BMP S102 for disposal options. • Inlet protection as described in Volume II, BMP C220 must be used if dust, grit, wash water, or other pollutants may escape the work area. This is particularly necessary on rainy days. Provide inlet protection over the storm drain at the beginning of the work day. Do not perform outdoor work during wet weather if contaminants could be washed off-site by rainfall. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 39 Chapter 4 4.6.3.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • Recycle materials whenever possible. • Light spraying of water on the work site can control some of the dust and grit that can blow away. Oils must never be used for dust control. Never spray to the point of runoff from the site. • Activities such as tool cleaning should occur over a ground cloth or within a containment device such as a tub. • Catch basin filter inserts may be considered. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 40 Chapter 4 4.7 Dust Control, and Soil and Sediment Control 4.7.1 BMP A601: Dust Control at Disturbed Land Areas and Unpaved Roadways and Parking Lots 4.7.1.1 Description of Pollutant Sources Dust can cause air and water pollution problems particularly at demolition sites, disturbed land areas, and unpaved roadways and parking lots. 4.7.1.2 Pollutant Control Approach Minimize dust generation and apply environmentally friendly and government approved dust suppressant chemicals, if necessary. 4.7.1.3 Required BMPs • Sprinkle or wet down soil or dust with water as long as it does not result in runoff or a wastewater discharge. Minimize the amount of water to avoid washing pollutants into the storm drainage system. At active construction sites, street sweeping shall be performed prior to washing the street. • Use only local and/or state government approved dust suppressant chemicals such as those listed in Ecology Publication #96-433, “Techniques for Dust Prevention and Suppression.” See BMP C126, Polyacrylamide for Soil Erosion Protection, in Volume II, Chapter 3 of this manual. • Avoid excessive and repeated applications of dust suppressant chemicals. Time the application of dust suppressants to avoid or minimize their wash-off by rainfall or human activity such as irrigation. • Use stormwater containment to prevent the conveyance of solids by stormwater into storm drains or receiving waters. • The use of motor oil or other oils for dust control is prohibited. Care shall be taken when using lignin derivatives and other high BOD chemicals in excavations or areas easily accessible to surface water or groundwater. • Consult with the Ecology Northwest Regional Office at 425-649-7000 on discharge permit requirements if the dust suppression process results in a wastewater discharge to the ground, groundwater, storm drain, or surface water. 4.7.1.4 Recommended BMPs for Roadways and Other Trafficked Areas: • Consider limiting use of off-road recreational vehicles on dust generating land. • Consider paving unpaved permanent roads, approaches, exits, access lanes, and other trafficked areas at municipal, commercial, and industrial areas. • Consider paving or stabilizing shoulders of paved roads with gravel, vegetation, or City of Auburn approved chemicals. • Encourage use of alternate paved routes, if available. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 41 Chapter 4 • Vacuum or wet sweep fine dirt and skid control materials from paved roads soon after winter weather ends or as needed. • Consider using traction sand that is pre-washed to reduce dust emissions. 4.7.1.5 Recommended BMPs for Dust Generating Areas: • Prepare a dust control plan. Helpful references include: Control of Open Fugitive Dust Sources (EPA-450/3-88-088) and Fugitive Dust Background Document and Technical Information Document for Best Available Control Measures (EPA-450/2-92-004). • Limit exposure of soil (dust source) as much as feasible. • Stabilize dust-generating soil by growing and maintaining vegetation, mulching, topsoiling, and/or applying stone, sand, or gravel. • Apply windbreaks in the soil such as trees, board fences, tarp curtains, bales of hay, etc. • Cover dust-generating piles with wind-impervious fabric, or equivalent material. Additional information on dust control can be found in Volume II of this manual. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 42 Chapter 4 4.7.2 BMP A602: Dust Control at Manufacturing Sites 4.7.2.1 Description of Pollutant Sources Industrial material handling activities can generate considerable amounts of dust that is typically removed using exhaust systems. This can generate air emissions that can contaminate stormwater. Dusts can be generated at cement and concrete product mixing facilities, foundries, and wherever powdered materials are handled. Particulate materials that are of concern to air pollution control agencies include grain dust, sawdust, coal, gravel, crushed rock, cement, and boiler fly ash. The objective of this BMP is to reduce the stormwater pollutants caused by dust generation and control. 4.7.2.2 Pollutant Control Approach Prevent dust generation and emissions where feasible, regularly clean-up dust that can contaminate stormwater, and convey dust contaminated stormwater to to proper treatment. 4.7.2.3 Required BMPs • Clean building roofs, powder material handling equipment, and vehicles that can be sources of stormwater pollutants as needed to remove accumulated dust and residue. • Regularly sweep dust accumulation areas that can contaminate stormwater. Sweeping shall be conducted using vacuum filter equipment to minimize dust generation and to ensure optimal dust removal. • Minimize the amount of water used for dust control to avoid washing pollutants into the storm drainage system. 4.7.2.4 Recommended BMPs • In manufacturing operations, train employees to handle powders carefully to prevent generation of dust. • Use dust filtration/collection systems such as bag house filters, cyclone separators, etc. to control vented dust emissions that could contaminate stormwater. It may be necessary to monitor rooftops for possible accumulations of materials and take appropriate measures to prevent this material from entering the storm drainage system. Control of dust at foundries, metal shredders, and material transfer and handling facilities are some examples. • Use water spray to flush dust accumulations to sanitary sewers where allowed by the City of Auburn or to other appropriate treatment system. • Use approved dust suppressants such as those listed in Ecology Publication “Techniques for Dust Prevention and Suppression,” #96-433. (Ecology, 2003). Application of some products may not be appropriate in close proximity to receiving waters or conveyances close to receiving waters. For more information check with the Ecology Northwest Regional Office or the City of Auburn. • For removal of TSS in stormwater, use sedimentation basins, wet ponds, wet vaults, catch basin filters, vegetated filter strips, or equivalent sediment removal BMPs. Refer to Volume V for more information about these BMPs. • Additional information on dust control can be found in Volume II of this manual. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 43 Chapter 4 4.7.3 BMP A603: Soil Erosion and Sediment Control at Industrial Sites 4.7.3.1 Description of Pollutant Sources Industrial activities on soil areas, exposed and disturbed soils, steep grades, etc. can be sources of sediments that can contaminate stormwater runoff. 4.7.3.2 Pollutant Control Approach Limit the exposure of erodible soil, stabilize or cover erodible soil where necessary to prevent erosion, and/or provide treatment for stormwater contaminated with TSS caused by eroded soil. 4.7.3.3 Required BMPs Apply one or more of the following cover practices: • Vegetative cover such as grass, trees, large bark, bonded fiber matrix, or shrubs on erodible soil areas; • Covering with mats such as clear plastic, jute, synthetic fiber; or gunite; and/or • Preservation of natural vegetation including grass, trees, shrubs, and vines. Control sediment through installing a vegetated swale, dike, silt fence, check dam, gravel filter berm, and/or sedimentation basin and properly grading. For design information refer to Volume II. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 44 Chapter 4 4.8 Other Activities 4.8.1 BMP A701: Commercial Animal Handling Areas 4.8.1.1 Description of Pollutant Sources Racetracks, kennels, fenced pens, veterinarians, and businesses that provide boarding services for horses, dogs, cats, etc. can generate pollutants from activities such as manure deposits, animal washing, grazing, and any other animal handling activity that could contaminate stormwater. Pollutants can include coliform bacteria, nutrients, and total suspended solids. 4.8.1.2 Pollutant Control Approach To prevent, to the maximum extent practicable, the discharge of contaminated stormwater from animal handling and keeping areas. 4.8.1.3 Required BMPs • Regularly scoop, sweep and clean animal keeping areas to collect and properly dispose of droppings, uneaten food, and other potential stormwater contaminants. • Do not hose down to storm drains or receiving waters those areas that contain potential stormwater contaminants. • Contaminated water must go to the sanitary sewer. A hair and sediment trap may be required. • Do not allow any wash water to be discharged to storm drains or to receiving water without proper treatment. • If animals are kept in unpaved and uncovered areas, the ground must either have vegetative cover or some other type of ground cover, such as mulch. • If animals are not leashed or in cages, the area where animals are kept must be surrounded by a fence or other devices to prevent animals from moving away from the controlled area where BMPs are used. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 45 Chapter 4 4.8.2 BMP A702: Log Sorting and Handling 4.8.2.1 Description of Pollutant Sources Log yards are paved or unpaved areas where logs are transferred, sorted, debarked, cut, and stored to prepare them for shipment or for the production of dimensional lumber, plywood, chips, poles, or other products. Log yards are generally maintained at sawmills, shipping ports, and pulp mills. Typical pollutants include oil and grease, BOD, settleable solids, total suspended solids (including soil), high and low pH, heavy metals, pesticides, wood-based debris, and leachate. The following are pollutant sources: • Log storage, rollout, sorting, scaling, and cutting areas • Log and liquid loading areas • Log sprinkling • Debarking, bark bin, and conveyor areas • Bark, ash, sawdust and wood debris piles, and other solid wastes • Metal salvage areas • Truck, rail, ship, stacker, and loader access areas • Log trucks, stackers, loaders, forklifts, and other heavy equipment • Maintenance shops and parking areas • Cleaning areas for vehicles, parts, and equipment • Storage and handling areas for hydraulic oils, lubricants, fuels, paints, liquid wastes, and other liquid materials • Pesticide usage for log preservation and surface protection • Application of herbicides for weed control • Contaminated soil resulting from leaks or spills of fluids 4.8.2.2 Ecology’s Baseline General Permit Requirements Industries with log yards are required to obtain coverage under the baseline General Permit for Discharges of Stormwater Associated with Industrial Activities to Surface Water. The permit requires preparation and on-site retention of Stormwater Pollution Prevention Plans (SWPPP). The SWPPP must identify operational, source control, erosion and sediment control, and, if necessary, treatment BMPs. Required and recommended operational, source control, and treatment BMPs are presented in detail in Ecology’s Guidance Document: Industrial Stormwater General Permit Implementation Manual for Log Yards, Publication # 04-10-031. It is recommended that all log yard facilities obtain a copy of this document. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 46 Chapter 4 4.8.3 BMP A703: Boat Building, Maintenance and Repair 4.8.3.1 Description of Pollutant Sources Sources of pollutants at boat and ship building, repair, and maintenance facilities include pressure washing, surface preparation, paint removal, sanding, painting, engine maintenance and repairs, and material handling and storage, if conducted outdoors. Potential pollutants include spent abrasive grits, solvents, oils, ethylene glycol, wash water, paint over-spray, cleaners/detergents, anti-corrosive compounds, paint chips, scrap metal, welding rods, resins, glass fibers, dust, and miscellaneous trash. Pollutant constituents include TSS, oil and grease, organics, copper, lead, tin, and zinc. Related activities are covered under the following activity headings in this manual, and other BMPs provided in this manual: • A103 Washing, Pressure Washing, and Steam Cleaning of Vehicles/Equipment/Building Structures • A202 Fueling at Dedicated Stations • A714 Spills of Oil and Hazardous Substances 4.8.3.2 Pollutant Control Approach Apply good housekeeping, preventive maintenance, and cover and containment BMPs in and around work areas. 4.8.3.3 Required BMPs The following BMPs or equivalent measures are required of all businesses, public agencies, and private boat owners engaged in boat building, mooring, maintenance and repair that are not covered by the NPDES permit for boatyards: • Maintenance and repair activities that can be moved on-shore must be moved accordingly. This action reduces some of the potential for direct pollution impact on waterbodies. • Blasting and spray painting activities must be sheltered by hanging tarps to block the wind and prevent dust and overspray from escaping. Move the activity indoors if possible. See Chapter 5 for details on Puget Sound Clean Air Agency limitations. • Bermed ground cloths must be used for collection of drips and spills in painting and finishing operations, and paint chips and used blasting sand from sand blasting. • Collect spent abrasives regularly and store under cover to await proper disposal. • Dispose of greasy rags, oil filters, air filters, batteries, spent coolant, and degreasers properly. • Drain oil filters before disposal or recycling. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 47 Chapter 4 • Bilge water must be collected for proper disposal rather than discharged on land or water. See BMP S102 for detail on disposal options. Discharge of contaminated bilge water may be avoided if oil-absorbent pads are used to capture the oil in the bilge water before or during pumping. If pads are used, they must be recycled or properly disposed. • Convey sanitary sewage to pump-out stations, portable on-site pump-outs or other appropriate onshore facilities. • Maintenance yard areas must be swept and cleaned, without hosing down the area, at least once per week or as needed. This prevents sandblasting materials, scrapings, paint chips, oils, and other loose debris from being carried away with stormwater. The collected materials must be disposed of properly. See BMP S102 for disposal options. • Docks and boat ramps must be swept at least once per week or as needed and the collected materials must be disposed of properly. • Paint and solvent mixing, fuel mixing and similar handling of liquids shall be performed on shore, or such that no spillage can occur directly into surface waterbodies. • Routine cleanup materials such as oil-absorbent pads, brooms, dustpans, mops, buckets, and sponges must be stocked near docks. • Comply with BMP A203 and A101 if engine repair and maintenance are conducted. • In the event of an accidental discharge of oil or hazardous material into waters of the state or onto land with a potential for entry into state waters, immediately notify the Department of Ecology, and the National Response Center at 1-800-424-8802 (24 hour). 4.8.3.4 Recommended BMPs The following BMPs are not required but can provide additional pollution protection: • Boat construction and structural repair activities should be covered. • Materials such as paints, tools, and ground cloths should be stored indoors or in a covered area when not in use. • Select the least toxic anti-fouling paint available. • Use sanders that have dust containment bags and avoid sanding in windy conditions. • All used oil should be recycled if feasible. To dispose of filters, let drain 24 hours, then double wrap in plastic and dispose in the regular garbage. Pending state legislation may make disposal in the garbage illegal, so call the Hazardous Waste Line at 1-800-287-6429 for current information. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 48 Chapter 4 • Use one of the following treatment BMPs when paint chips or blasting grit are prevalent in the work area o Catch basin filter insert o Infiltration basin o Wet pond or vault o Constructed wetland o Vegetated biofilter o Filtration with media designed for the pollutants that are present o Equivalent BMP (see Volume V) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 49 Chapter 4 4.8.4 BMP A704: Logging 4.8.4.1 Description of Pollutant Sources This activity covers logging activities that fall under the Washington State Forest Practices Act category of Class IV general forest practices. These are situations where timber harvesting is done in the process of converting forest lands into other land uses, such as home and business construction. Stormwater runoff from bare ground can be loaded with dirt and other pollutants. This material can clog ditches and stream channels, thus reducing carrying capacity and increasing flooding, as well as smothering spawning beds for fish. Simply controlling runoff and not allowing it to leave the site will prevent these harmful effects. Clearing and grading activities are covered in detail in Volume II of this manual, Construction Stormwater Pollution Prevention. Grading activities are also regulated in the City of Auburn by the Land Clearing, Filling and Grading Code, Chapter 15.74 ACC. Control of stormwater run-on and soil stabilization is critical. Limiting the area to be cleared and graded during wet weather seasons will make site stabilization and sediment control easier. Coverage under Ecology’s Construction Stormwater General Permit is required for construction sites that result in the disturbance of one acre or more of land. Compliance with the Construction Stormwater Pollution Prevention requirements in Ecology’s manual is required, as applicable. Virtually all logging operations will require a permit from the Washington State Department of Natural Resources. Sensitive/critical areas and wetlands ordinances for Auburn also contain requirements for logging activities in the vicinity of water bodies. Pollutants of concern include suspended solids, oils and greases, biochemical oxygen demand (BOD), nutrients, toxic organic compounds, and heavy metals. 4.8.4.2 Pollutant Control Approach Maintain required buffers adjacent to critical areas, including streams and wetlands. Keep sediments out of waterbodies and off paved areas. 4.8.4.3 Required BMPs • Vegetation along stream corridors, and adjacent to other waterbodies and wetlands, must be preserved. Maintenance of a vegetated buffer enables filtration of most of the pollutants of concern for this activity. The above-mentioned ordinances contain specific requirements for buffer setbacks. • Logging access roads must have a crushed rock or spall apron construction entrance where they join the pavement to prevent sediments from being tracked onto the pavement. • On-site fueling and maintenance operations must follow the required BMPs as outlined in A204 Mobile Fueling; A203 Vehicle Maintenance; and A407 Storage of Liquid, Food Waste, or Dangerous Waste Containers. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 50 Chapter 4 4.8.4.4 Recommended BMPs The following BMPs are not required, but can provide additional pollution protection: • Erosion potential can be reduced by avoiding logging on steep slopes. • If access roads are constructed for logging, they should be provided with drainage ditches that divert runoff into vegetated areas or stormwater treatment systems. • Plant vegetated buffers in areas where they are already downslope of proposed logging areas, with sufficient lead time to allow for effective growth. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 51 Chapter 4 4.8.5 BMP A705: Mining and Quarrying of Sand, Gravel, Rock, Peat, Clay and Other Materials 4.8.5.1 Description of Pollutant Sources This activity applies to surface excavation and on-site storage of sand, gravel, and other materials that are mined. All mining operations that have stormwater runoff from the site are required to apply for a National Pollutant Discharge Elimination System (NPDES) permit with the Department of Ecology. Ecology has specific BMPs required by the permit. Some additional BMPs to help meet Ecology’s discharge performance standards are listed below. Other permits from the Washington Department of Natural Resources and the City of Auburn may be required. Pollutants of concern are suspended solids, nutrients, pH, oils, and metals. Pollutant Control Approach: Provide containment and or cover for any on-site storage areas to prevent run-on on and discharge of suspended solids and other pollutants. 4.8.5.2 Recommended BMPs • If the material is appropriate, use excavated spoil material to form compacted berms along downslope sides of the site to contain runoff. Berms should be seeded to promote growth of grass or other vegetation to limit erosion from the berms. Safety measures to prevent flooding due to berm failure shall be considered. • Measures to control track-out and dust should be implemented. Wheel washes, sweeping, and paving high traffic areas are some common practices. • Semi-permanent stockpiles should be seeded to promote vegetation growth which can help to limit erosion from the stockpiles. • Use sediment ponds to promote settling of suspended solids. Refer to Volume V of this manual for more information. • Use anchored tarps to cover stockpiles at small-scale mining operations if there is a potential for contaminated stormwater to leave the site. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 52 Chapter 4 4.8.6 BMP A706: Swimming Pool and Spa Cleaning and Maintenance 4.8.6.1 Description of Pollutant Sources This activity applies to all municipal and commercial swimming pools and spas. Pools and spas at hotels, motels, and apartment and condominium complexes are covered here. Pools at single-family residences are covered in Chapter 3 of this volume. Commercial pool and spa cleaning services must follow the required BMPs for all pools serviced. Pollutants of concern include nutrients, suspended solids, chlorine, pH, and chemical oxygen demand (COD). 4.8.6.2 Pollutant Control Approach Dispose of pool or spa water to the sanitary sewer. 4.8.6.3 Required BMPs • The preferred method of pool or spa water disposal is to the sanitary sewer. If a sanitary sewer is available, all Health Department regulated facilities are required to connect for draining and backwash. Contact the City of Auburn Sanitary Sewer Utility at 253-931-3010 prior to discharge for instructions on allowable flow rates and timing before starting to drain the pool. Never discharge pool water to a septic system, as it may cause the system to fail. • If discharge to the sanitary sewer is not possible, pool and spa water may be discharged to a ditch or storm drainage system, provided that the water has been dechlorinated first. The proponent is required to contact the City of Auburn Storm Drainage Utility at 253-931-3010 prior to discharge for instructions on allowable flow rates for the system or ditch that is being discharged to. All discharges shall be dechlorinated to a concentration of 0.1 parts per million (ppm or mg/L) or less, and pH adjusted 6.5 to 8.5 standard units, if necessary. Neutralizing chemicals are available for dechlorinating water and adjusting the pH. Turbidity shall not exceed 10 NTU. Letting the pool or spa "sit" may also reduce chlorine levels. Use a test kit to determine if the chlorine concentration has reached zero and the pH is within acceptable limits. • State law allows discharges of pool water to the ground, not to a water body or storm drainage system, with a chlorine level of up to 3 parts per million. However, the water must not cross property lines or impact neighboring properties, and a satisfactory means for distributing the water to the ground must be used so there is no runoff. • Backwash from pool filters cannot be discharged to surface waters, storm drainage systems, septic systems, or on the ground. • Diatomaceous earth used in pool filters cannot be discharged to surface waters, storm drainage systems, septic systems, or on the ground. 4.8.6.4 Recommended BMP • Hire a professional pool-draining service to collect all pool water for offsite disposal. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 53 Chapter 4 4.8.7 BMP A707: De-Icing and Anti-Icing Operations for Streets & Highways 4.8.7.1 Description of Pollutant Sources Deicing and/or anti-icing compounds are used on highways, streets, and sidewalks to control ice and snow. Typically ethylene glycol and propylene glycol are deicers used on aircraft. Deicers commonly used on highways, streets and sidewalks include calcium magnesium acetate (CMA), calcium chloride, magnesium chloride, sodium chloride, urea, and potassium acetate. The deicing and antiicing compounds become pollutants when they are conveyed to storm drains or to surface water after application. Leaks and spills of these chemicals can also occur during their handling and storage. 4.8.7.2 Required BMPs • Select de-icers and anti-icers that cause the least adverse environmental impact. Apply only as needed using minimum quantities. • Where feasible and and practicable, use roadway deicers, such as calcium magnesium acetate, potassium acetate, or similar materials that cause less adverse environmental impact than urea and sodium chloride. • Store and transfer de/anti-icing materials on an impervious containment pad in accordance with BMP A401 Storage or Transfer (Outside) of Solid Raw Materials, By-Products, or Finished Products and A408 Storage of Liquids in Above-Ground Tanks. • Sweep/clean up accumulated de/anti-icing materials and grit from roads as soon as possible after the road surface clears. 4.8.7.3 Recommended BMPs • Intensify roadway cleaning in early spring to help remove particulates from road surfaces. • Include limits on toxic metals in the specifications for de/anti-icers. • Additional guidance can be found in the Regional Road Maintenance -Endangered Species Act (ESA) program guidelines. • State guidelines contain additional information for de-icing activities at airports. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 54 Chapter 4 4.8.8 BMP A708: Roof and Building Drains at Manufacturing and Commercial Buildings 4.8.8.1 Description of Pollutant Sources Stormwater runoff from roofs and sides of manufacturing and commercial buildings can be sources of pollutants caused by leaching of roofing materials, building vents, and other air emission sources. Vapors and entrained liquid and solid droplets/particles have been identified as potential pollutants in roof/building runoff. Metals, solvents, acidic/alkaline pH, BOD, and organics are some of the pollutant constituents identified. 4.8.8.2 Pollutant Control Approach Evaluate the potential sources of stormwater pollutants and apply source control BMPs where feasible. Use dust filtration/collection systems such as bag house filters, cyclone separators, etc. to control vented dust emissions that could contaminate stormwater. It may be necessary to monitor roof tops for possible accumulations of materials and take appropriate measures to prevent this material from entering the storm drainage system. Control of dusts at foundries, metal shredders, and material transfer and handling facilities are some examples. 4.8.8.3 Required BMPs • Bare galvanized metal shall not be used for materials that convey stormwater, such as roofs, canopies, siding, gutters, downspouts, roof drains, and pipes. Any galvanized materials shall have an inert, non-leachable finish, such as baked enamel, fluorocarbon paint (such as Kynaror Hylar), factory-applied epoxy, pure aluminum, or asphalt coating. Acrylic paint, polyester paint, field-applied, and part zinc (such as Galvalume) coatings are not acceptable. • If leachates and/or emissions from buildings are suspected sources of stormwater pollutants, then sample and analyze the stormwater draining from the building. • If a roof/building stormwater pollutant source is identified, implement appropriate source control measures such as air pollution control equipment, selection of materials, operational changes, material recycle, process changes, etc. • Water quality treatment BMPs are found in Volume V of this manual. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 55 Chapter 4 4.8.9 BMP A709: Urban Streets 4.8.9.1 Description of Pollutant Sources Streets can be sources of vegetative debris, paper, fine dust, vehicle liquids, tire wear residues, heavy metals (lead and zinc), phthalates, soil particles, ice control salts, domestic wastes, animal wastes, lawn chemicals, and vehicle combustion by-products. Street surface contaminants have been found to contain significant concentrations of particle sizes less than 250 microns (Sartor and Boyd, 1972). 4.8.9.2 Pollutant Control Approach Conduct efficient street sweeping where and when appropriate to minimize the contamination of stormwater. Do not wash street debris into storm drains. 4.8.9.3 Recommended BMPs • For maximum stormwater pollutant reductions on curbed streets and high volume parking lots, use efficient vacuum sweepers. • High-efficiency street sweepers utilize strong vacuums vacuums and the mechanical action of main and gutter brooms combined with an air filtration system that only returns clean air to the atmosphere (i.e., filters very fine particulates). They sweep dry and use no water since they do not emit any dust. • For moderate stormwater pollutant reductions on curbed streets, use regenerative air sweepers or tandem sweeping operations. • A tandem sweeping operation involves a single pass of a mechanical sweeper followed immediately by a single pass of a vacuum sweeper or regenerative air sweeper. o A regenerative air sweeper blows air down on the pavement to entrain particles and uses a return vacuum to transport the material to the hopper. o These operations usually use water to control dust. This reduces their ability to pick up fine particulates. • For minimal stormwater pollutant reductions on curbed streets, use mechanical sweepers. NOTE: Mechanical sweepers are referred to as broom sweepers and use the mechanical action of main and gutter brooms to throw material material on a conveyor belt that transports it to the hopper. These sweepers usually use water to control dust, reducing their ability to pick up fine particulates. • Conduct sweeping at optimal frequencies. Optimal frequencies are those scheduled sweeping intervals that produce the most cost-effective annual reduction of pollutants normally found in stormwater and can vary depending on land use, traffic volume, and rainfall patterns. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 56 Chapter 4 • Train operators in those factors that result in optimal pollutant removal. These factors include sweeper speed, brush adjustment and rotation rate, sweeping pattern, maneuvering around parked vehicles, and interim storage and disposal methods. • Minimize the amount of water applied for dust control to avoid washing pollutants into the storm drainage system. • At active construction sites, street sweeping shall be performed prior to washing the street. • Consider the use of periodic parking restrictions and public notification in residential areas to ensure the sweeper’s ability to sweep along the curb. • Establish procedures for prompt sweeping, removal, and disposal of spill clean-up materials and debris from special events that will generate higher than normal loadings. • Disposal of street sweeping solids must comply with “Recommendations for Management of Street Wastes” described in Appendix D of this volume. Additional guidance can be found in the Regional Road Maintenance – Endangered Species Act (ESA) program guidelines. • Inform citizens about the importance of eliminating yard debris, oil, and other wastes in street gutters in order to reduce street pollutant sources. • When encountering questionable sweeping waste contact the City of Auburn Storm Drainage Maintenance and Operations at 253-931-3048. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 57 Chapter 4 4.8.10 BMP A710: Railroad Yards 4.8.10.1 Description of Pollutant Sources Pollutant sources can include drips/leaks of vehicle fluids and cargo onto the railroad bed; human waste disposal; litter; locomotive/railcar/equipment cleaning; fueling; outside material storage; the erosion and loss of soil particles from the railroad bed; maintenance and repair activities at railroad terminals, switching yards, and maintenance yards; and herbicides used for vegetation management. Waste materials can include waste oil, solvents, degreasers, antifreeze solutions, radiator flush, acids, brake fluids, dust, soiled rags, oil filters, sulfuric acid and battery sludge, machine chips with residual machining oil, and toxic fluids/solids lost during transit. Potential pollutants include oil and grease, TSS, BOD, organics, pesticides, and metals. 4.8.10.2 Pollutant Control Approach Apply good housekeeping and preventive maintenance practices to control leaks and spills of liquids in railroad yard areas. 4.8.10.3 Required BMPs • Implement the applicable BMPs in this chapter depending on the pollutant generating activities/sources at a railroad yard facility. • Do not allow toilets to discharge to outside areas while a train is in transit or at the station. Pump-out facilities shall be used to service train toilets. • Use drip and track pans at hose/pipe connections during liquid transfer and other leak-prone areas. • During maintenance do not discard debris or waste liquids along the tracks or in railroad yards. • Promptly clean up all spilled materials. In areas subjected to leaks/spills of oils or other chemicals, convey the contaminated stormwater to appropriate treatment such as a sanitary sewer (if approved by the City of Auburn), to a CP or API oil/water separator for floating oils, or other appropriate treatment BMP (as approved by the City of Auburn). See Volume V. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 58 Chapter 4 4.8.11 BMP A711: Maintenance of Public and Utility Corridors and Facilities 4.8.11.1 Description of Pollutant Sources Passageways and equipment at petroleum product, natural gas, and water pipelines and electrical power transmission corridors and rights-of-way can be sources of pollutants, such as herbicides used for vegetation management and eroded soil particles from unpaved access roads. At pump stations, waste materials generated during maintenance activities may be temporarily stored outside. Additional potential pollutant sources include the leaching of preservatives from wood utility poles, PCBs in older transformers, water that is removed from underground transformer vaults, and leaks/spills from petroleum pipelines. The following are potential pollutants: oil and grease, TSS, BOD, organics, PCB, pesticides, and heavy metals. 4.8.11.2 Pollutant Control Approach Control fertilizer and pesticide applications, soil erosion, and site debris that can contaminate stormwater. 4.8.11.3 Required BMPs • Implement BMPs included in Chapter 4, BMP A306: Landscaping and Lawn/Vegetation Management. • When water or sediments are removed from electric transformer vaults, determine whether contaminants might be present before disposing of the water and sediments. This includes inspecting for the presence of oil or sheen, and determining from records or testing if the transformers contain PCBs. If records or tests indicate that the sediment or water are contaminated above applicable levels, manage these media in accordance with applicable federal and state regulations, including the federal PCB rules (40 CFR 761) and the state MTCA cleanup regulations (Chapter 173-340 WAC). Water removed from the vaults can be discharged in accordance with the federal 40 CFR 761.79, and state regulations (Chapter 173-201A WAC and Chapter 173-200 WAC), or via the sanitary sewer if the requirements, including applicable permits, for such a discharge are met. (See also Chapter 5). • Within utility corridors, consider preparing maintenance procedures and an implementation schedule that provides for vegetative, gravel, or equivalent cover that minimizes bare or thinly vegetated ground surfaces within the corridor to prevent the erosion of soil. Pave high traffic corridors. • Provide maintenance practices to prevent stormwater from accumulating and draining across and/or onto roadways. Stormwater shall be conveyed through roadside ditches and culverts. The road shall be crowned, out-sloped, water barred, or otherwise left in a condition not conducive to erosion. Appropriately maintaining grassy roadside ditches discharging to surface waters is an effective way of removing some pollutants associated with sediments carried by stormwater. • Maintain ditches and culverts at an appropriate frequency to ensure that plugging and flooding across the roadbed, with resulting overflow erosion, does not occur. occur. • Apply the appropriate BMPs from Volume IV for the storage of waste materials that can contaminate stormwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 59 Chapter 4 4.8.11.4 Recommended BMPs • When selecting utility poles for a specific location, consideration should be given to the potential environmental effects of the pole or poles during storage, handling, and end-use, as well as its cost, safety, efficacy, and expected life. If a wood product treated with chemical preservatives is used, it should be made in accordance with generally accepted industry standards such as the American Wood Preservers Association Standards. If the pole or poles will be placed in or near an environmentally sensitive area, such as a wetland or a drinking water well, alternative materials or technologies should be considered. These include poles constructed with material(s) other than wood, such as fiberglass composites, metal, or concrete. Other technologies and materials, such as sleeves or caissons for wood poles, may also be considered when they are determined to be practicable and available. • Ring the base of treated poles with adsorbent material if leaching of preservative may occur. Monitor the adsorbents as needed. • As soon as practicable, remove all litter from wire cutting/replacing operations, etc. • Implement temporary erosion and sediment control in areas where clear-cuts are conducted and new roads are constructed. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 60 Chapter 4 4.8.12 BMP A712: Maintenance of Roadside Ditches 4.8.12.1 Description of Pollutant Sources Common road debris including litter, eroded soil, oils, vegetative particles, and heavy metals can be sources of stormwater pollutants. 4.8.12.2 Pollutant Control Approach Roadside ditches should be maintained to preserve the condition and capacity for which they were originally constructed, and to minimize bare or thinly vegetated ground surfaces. Maintenance practices should provide for erosion and sediment control (Refer to BMP A306 Landscaping and Lawn/Vegetation Management). 4.8.12.3 Required BMPs • Inspect roadside ditches regularly, as needed, to identify sediment accumulations and localized erosion. • Clean ditches on a regular basis, as needed. Ditches shall be kept free of rubbish and debris. • Vegetation in ditches often prevents erosion and cleanses runoff waters. Remove vegetation only when flow is blocked or excess sediments have accumulated. Conduct ditch maintenance (seeding, fertilizer application, harvesting) in late spring and/or early fall, where possible. Consider leaving segments of undisturbed vegetation to provide natural filtration. • In the area between the edge of the pavement and the bottom of the ditch, commonly known as the “bare earth zone,” use grass vegetation, wherever possible. Vegetation shall be established from the edge of the pavement if possible or at least from the top of the slope of the ditch. • Diversion ditches on top of cut slopes that are constructed to prevent slope erosion by intercepting surface drainage must be maintained to retain their diversion shape and capability. • Ditch cleanings are not to be left on the roadway surfaces. Sweep dirt and debris remaining on the pavement at the completion of ditch cleaning operations. • Roadside ditch cleanings not contaminated by spills or other releases and not associated with a stormwater treatment system such as a bioswale may be screened to remove litter and separated into soil and vegetative matter (leaves, grass, needles, branches, etc.). The soil fraction may be handled as ‘clean soils’ and the vegetative matter can be composted or disposed of in a municipal waste landfill. For more information, please see “Recommendations for Management of Street Wastes,” in Appendix D of this volume. • Roadside ditch cleanings contaminated by spills or other releases known or suspected to contain dangerous waste must be handled following the Dangerous Waste Regulations (Chapter 173-303 WAC) unless testing determines it is not dangerous waste. Specific cleanup standards are set forth in the Model Toxics Control Act (Chapter 70.105D RCW) and Regulations (Chapter 173-340 WAC). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 61 Chapter 4 • Inspect culverts on a regular basis for scour or sedimentation at the inlet and outlet, and repair as necessary. Give priority to those culverts conveying perennial and/or salmon-bearing streams and culverts near streams in areas of high sediment load, such as those near subdivisions during construction. 4.8.12.4 Recommended BMPs • Install biofiltration swales and filter strips to treat roadside runoff wherever practicable and use engineered topsoils wherever necessary to maintain adequate vegetation. These systems can improve infiltration and stormwater pollutant control upstream of roadside ditches. Refer to Volume V of this manual for additional information about biofiltration swales and filter strips. • Additional guidance can be found in the Regional Road Maintenance -Endangered Species Act (ESA) program guidelines. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 62 Chapter 4 4.8.13 BMP A713: Maintenance of Stormwater Drainage and Treatment Facilities 4.8.13.1 Description of Pollutant Sources Facilities include roadside catch basins on arterials and within residential areas, conveyance systems, detention facilities such as ponds and vaults, oil and water separators, biofilters, settling basins, infiltration systems, and all other types of stormwater treatment systems presented in Volume V. Roadside catch basins can remove from 5 to 15 percent of the pollutants present in stormwater. When catch basins are about 60 percent full of sediment, they cease removing sediments. Oil and grease, hydrocarbons, debris, heavy metals, sediments, and contaminated water are found in catch basins, oil and water separators, settling basins, etc. 4.8.13.2 Pollutant Control Approach Provide maintenance and cleaning of debris, sediments, and oil from stormwater collection, conveyance, and treatment systems to obtain proper operation. 4.8.13.3 Required BMPs Maintain stormwater treatment facilities according to the O&M procedures presented in Volume I, Appendix D, in addition to the following BMPs: • Inspect and clean treatment BMPs, conveyance systems, and catch basins as needed, and determine whether improvements in O&M are needed. • Promptly repair any deterioration threatening the structural integrity of the facilities. These include replacement of clean-out gates, catch basin lids, and rock in emergency spillways. • Ensure that storm sewer capacities are not exceeded and that heavy sediment discharges to the sewer system are prevented. • Regularly remove debris and solids from BMPs used for peak-rate control, treatment, etc. and discharge to a sanitary sewer if approved by the City of Auburn, or truck to a local or state government approved disposal site. • Clean catch basins in accordance with the information provided in Volume I, Appendix D. Additional information is also included in BMP S109: Cleaning Catch Basins. • Clean debris in a catch basin as frequently as needed to ensure proper operation of the catch basin. • Post warning signs or curb markers; “Dump No Waste -Drains to Groundwater,” “Streams,” “Lakes,” or emboss on or adjacent to all storm drain inlets where practical. • Disposal of sediments and liquids from the catch basins must comply with “Recommendations for Management of Street Wastes” described in Appendix D of this volume. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 63 Chapter 4 • Select additional applicable BMPs from Chapter 4 of this volume depending on the pollutant sources and activities conducted at the facility. Those BMPs include: o A407 Storage of Liquid, Food Waste, or Dangerous Waste Containers. o A603 Soil Erosion and Sediment Control at Industrial Sites o A709 Urban Streets o A714 Spills of Oil and Hazardous Substances o S101 Eliminate Illicit Storm Drainage System Connections S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 64 Chapter 4 4.8.14 BMP A714: Spills of Oil and Hazardous Substances 4.8.14.1 Description of Pollutant Sources Owners or operators of facilities engaged in drilling, producing, handling, gathering, storing, processing, transferring, distributing, refining or consuming oil and/or oil products are required by Federal Law to have a Spill Prevention and Control Plan. The federal definition of oil is oil of any kind or any form, including, but not limited to, petroleum, fuel oil, sludge, oil refuse, and oil mixed with wastes other than dredged spoil. Specific regulations can be found in 40 CFR Part 112, as amended December, 2006. These regulations are administered by the Environmental Protection Agency and the United States Coast Guard. Large petroleum handling facilities and vessels are also subject to regulations contained in Chapter 90.56 RCW and Chapter 173-180A WAC. Owners of businesses that produce Dangerous Wastes are also required by State Law, Chapter 70.105 RCW and Chapter 173-303 WAC, to have a spill control plan. These businesses should refer to Chapter 5 of this volume. The City of Auburn may also require a spill plan to protect the municipal sewer system and groundwater resources. Plans required by the above listed regulations may suffice. 4.8.14.2 Pollutant Control Approach Maintain, update, and implement an oil spill prevention/cleanup plan. 4.8.14.3 Required BMPs • Prepare an Emergency Spill Control Plan (SCP), which includes: o A description of the facility including the owner's name and address. o The nature of the activity at the facility. o The general types of chemicals used or stored at the facility. o A site plan showing the location of storage areas for chemicals, the locations of storm and sanitary drains, the areas draining to them, the ultimate point of discharge, and the location and description of any devices to stop spills from leaving the site such such as positive control valves; o Cleanup procedures and supplies. o Notification procedures to be used in the event of a spill, such as notifying key personnel. Agencies such as Ecology, Valley Regional Fire Authority, Washington State Patrol, City of Auburn, and the U.S. Environmental Protection Agency shall be notified. o The name and 24-hour contact telephone number of the designated person, and their alternate with overall spill cleanup and notification responsibility. o Identify contractors that can be contacted to provide spill clean-up and disposal services. A service agreement is encouraged. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 65 Chapter 4 • Train key personnel in the implementation of the Emergency SCP. Prepare a summary of the plan and post it at appropriate points in the building, identifying the spill cleanup coordinators, location of cleanup kits, and 24-hour phone numbers of regulatory agencies to be contacted in the event of a spill. • Update the SCP regularly. • Immediately notify Ecology and the City of Auburn if a spill may reach sanitary or storm sewers, groundwater, or surface water, in accordance with federal and Ecology spill reporting requirements. • Immediately clean up spills using appropriate personal protection equipment and following the facility safety standards. Do not use emulsifiers for cleanup unless an appropriate disposal method for the resulting oily wastewater is implemented. Absorbent material shall not be washed down a floor drain or storm sewer. • Locate emergency spill containment and cleanup kit(s) in high potential spill areas. The contents of the kit shall be appropriate for the type and quantities of chemical liquids stored at the facility. 4.8.14.4 Recommended BMPs • Spill kits should include appropriately lined drums, absorbent pads, and granular or powdered materials for neutralizing acids or alkaline liquids where applicable. In fueling areas: absorbent should be packaged in small bags for easy use and small drums should be available for storage of absorbent and/or used absorbent. Spill kits should be deployed in a manner that allows rapid access and use by employees. • Example spill plans may be obtained from the Washington State Department of Transportation and the Environmental Protection Agency. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 66 Chapter 4 4.8.15 BMP A715: Water Reservoir, Transmission Mainline, Wellhead, and Hydrant Flushing Activities 4.8.15.1 Description of Pollutant Sources Construction and operation of drinking water infrastructure, as well as emergency response activities, can generate sediments, rust, turbidity and suspended solids, bacteria, and chlorinated water. Flushing of the water delivery system is necessary to maintain drinking water quality and ensure public health. Flushing activities can result in increased flows in downstream conveyances. These high flows may cause flooding and create erosion in downstream channels. 4.8.15.2 Pollutant Control Approach Establish operational controls for flow rate and volume of discharges, removal of sediments, neutralization of chlorine, and maximizing the beneficial use of the resource. 4.8.15.3 Required BMPs • Discharges of untreated hyperchlorinate water must go to the sanitary sewer. Prior City approval is required. • Alternatively, non-emergency discharges of de-chlorinated potable water may go to the storm drainage system at prior approved flow rates provided the following limits are met: o Chlorine residual 0.1 ppm o pH 6.5 – 8.5 • Evaluation of the receiving conveyance system for capacity and/or obstructions may be required. • City approval may be required for draining and flushing reservoirs, standpipes, wellheads, and transmission lines. Notification, monitoring, reporting, flow control measures, and other special conditions may apply. Contact the City of Auburn Public Works Department at 253-931-3010 for the requirements. • For routine hydrant and water main flushing, coordinate with the City of Auburn Storm Maintenance and Operations section at 253-931-3048. In all cases, the receiving storm pipe shall be monitored for the duration of the discharge to maintain half the full-pipe flow rate. 4.8.15.4 Recommended BMPs • During emergency repairs and activities, such as mainline breaks, erosion control measures shall be taken as practicable. Use of sandbags, check dams, plastic sheeting, pumps, and other erosion control measures should be employed to minimize erosion as much as possible. • Excavation de-watering should be managed to minimize downstream environmental impacts. Use of vactor trucks, diverting flow to grassy areas, filter bags, and retention ponds should be employed. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 67 Chapter 4 • Significant releases of water can have a detrimental effect on the storm and sanitary transmission system as well as receiving waters. Notification of these releases must be promptly made to the City by calling 253-931-3048. Figure IV-4-18. Hydrant Flushing S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 68 Chapter 4 4.8.16 BMP S101: Eliminate Illicit Storm Drainage System Connections A common problem found in storm drainage systems is illegal hook-ups to the system. Conversely, discharging clean, uncontaminated water to the sanitary sewer system is also prohibited. All businesses and residences in Auburn shall examine their plumbing systems to determine if illicit connections exist. Any time it is found that toilets, sinks, appliances, showers and bathtubs, floor drains, industrial process waters, cooling towers, or other indoor activities are connected to the storm drainage system, the connections must be immediately rerouted to the sanitary or septic system, holding tanks, or process treatment system. Exceptions to this requirement would be those industries and businesses that have been issued an NPDES Permit by Ecology, and are allowed specific discharges under that permit. Please refer to Chapter 5 to determine if a specific type of business is required to have a NPDES permit. Dye testing with a non-toxic dye, smoke testing, electronic locators, and television inspection equipment can help to determine where a pipe or structure drains if it is not obvious by observations or on plans. Contact the City of Auburn Public Works Department at 253-931-3010 for assistance in locating City structures adjacent to a property. Drains which are found to be connected to the wrong system must either be permanently plugged or disconnected and rerouted as soon as possible. Permits must be obtained from The City of Auburn (253-931-3090) to reroute drains. If the discharge is contaminated and sanitary service is not available, alternate measures will be necessary. If the discharge is simply domestic waste, a septic system may be feasible. Contact the appropriate County Health Department for a septic system permit. If the discharge is anything other than domestic, then a holding tank or on-on-site treatment may be necessary. Contact the City of Auburn Storm Drainage Utility at 253-931-3010 for assistance. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 69 Chapter 4 4.8.17 BMP S102: Dispose of Contaminated Stormwater and Waste Materials Properly Every business and residence in Auburn must dispose of solid and liquid wastes and contaminated stormwater properly. There are generally four options for disposal depending on the type of materials. These options include: • Sanitary sewer and septic systems • Recycling facilities • Municipal or private, permitted solid waste disposal facilities • Permitted hazardous waste treatment, storage, and disposal facilities Many liquid wastes and contaminated stormwater (depending on the pollutants and associated concentrations present) can be put into the sanitary sewer. Animal wastes can also be disposed of in a sanitary sewer. A permit may be required for discharges to the sanitary sewer system. Please contact the Auburn Utilities Section at 253-931-3010 for design and permit requirements. If wastes cannot be legally discharged to a sanitary sewer or septic system, one of the other three disposal options must be used. Recycling facilities are a recommended option for many commercial and household items, including used oils, used batteries, old equipment, glass, some plastics, metal scrap materials, solvents, paints, wood and land clearing wastes, and various other solid wastes. Solid wastes that cannot be recycled and that are not hazardous must be disposed of at a licensed municipal solid waste disposal facility. Dangerous and hazardous wastes must be properly transported to an appropriate hazardous waste treatment, storage, and disposal facility. The City of Auburn Solid Waste Utility at 253-931-3047 can provide information on waste disposal options. Maintain records for all materials that are recycled or disposed. Appendix A of this volume has a list of telephone numbers to contact for assistance. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 70 Chapter 4 4.8.18 BMP S103: Discharge Process Wastewater to a Sanitary Sewer, Holding Tank, or Water Treatment System This BMP is a minimum requirement for all industrial and commercial activities that generate contaminated process wastewater, such as washing activities, composting activities, and production and processing activities. The water used in these activities shall not drain to surface waters or groundwater untreated. Process water must drain to a sanitary sewer, holding tank, on-site treatment system, wastewater treatment system, or be recycled. In order to connect to the sanitary sewer, contact Auburn Permit Center at 253-931-3090 for information on sanitary sewer connection permits. Call the City of Auburn Sanitary Sewer Utility at 253-931-3010 for pretreatment and permit information. If a sanitary sewer is not available, the only remaining options are holding tanks or an on-site wastewater treatment facility. The contents of the holding tank must be pumped out or drained before the tank is full and disposed of properly (see BMP S102). If the on-site wastewater treatment facility option is taken, then it must be designed to receive and effectively treat all discharges of process water from the business. The Washington State Department of Ecology must be contacted for approval of such a facility. If the activity is to remain uncovered, then define a designated area for the activity and provide a mechanism for prevention of stormwater run-on into the activity area. (e.g. a curb, dike, or berm).The designated area shall be paved and sloped to a central collection drain and be connected to the sanitary sewer, (with pretreatment if required), the on-site holding tank, or the on-site treatment facility, whichever method is selected. Monitoring and maintaining all collection systems and keeping records of inspections and maintenance may be required. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 71 Chapter 4 4.8.19 BMP S108: Implement Integrated Pest Management Measures Use of herbicides, fungicides, and rodenticides should always be done with extreme caution, not only because of the potential harm to humans and pets, but also because of the potential harm to fish, wildlife, and our water resources. In light of the toxic nature of these compounds, special attention should be given to pesticide usage in all applications. The discussion below applies more to largescale licensed pesticide users, but should be considered for backyard applications as well. Commercial, agricultural, municipal, and other large scale pesticide users, such as golf courses and parks, should adhere to the principles of integrated pest management (IPM), a decision-making process for pest management that strives for intelligent, environmentally sound control of pests. It is a systems approach approach to pest management that combines agronomic, biological, chemical, and genetic information for educated decisions on the type of control to use, the timing and extent of chemical application, and whether non-chemical means can attain an acceptable level of pest control. IPM is a preventive measure aimed at knowing the exact pests being targeted for control, the locations and times when pests will pose problems, the level of pest-induced damage that can be tolerated without taking action, the most vulnerable life stage, and control actions that are least damaging to the environment. The major components of IPM are as follows: • Monitoring and inventory of pest populations • Determination of pest-induced injury and action levels • Identification of priority pest problems • Selection and timing of least toxic management tools • Site-specific treatment with minimized chemical use • Evaluation and adjustment of pesticide applications Monitoring of pest populations is a key to successful IPM implementation. Pest problems are universally easier to control if the problem can be discovered early. With IPM, pesticides are used only as a last resort. Maximization of natural controls, including biological controls and removal of pests by hand, is always the first choice. Additional concerns are storage, equipment clean-up, spill protocols, and waste disposal. More information on IPM is available from the Washington State Department of Agriculture and from the Washington State University Extension Service, or in Appendix C of this volume. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 72 Chapter 4 4.8.20 BMP S109: Cleaning Catch Basins Cleaning catch basins regularly is one of the most important stormwater source control measures that a business can take. Catch basins are typically located at low spots in parking lots, along curbs and road edges, and where storm drain pipes combine flows. Catch basins collect surface runoff for storm drains that are typically located directly underneath them. Most catch basins have some storage in the bottom that never drains to an outflow pipe. This permanent storage area is intended to trap sediments, debris, and other particles that can settle out of stormwater, thus preventing clogging of downstream pipes and washing of these solids into receiving waters. All of the solids and stagnant water collected from catch basin sumps must be disposed of properly. The sump contents shall not be flushed into the catch basin outflow pipe. For additional information on the maintenance of catch basins, refer to Volume I, Appendix D. Perform regular inspections of the basins and their grates. Remove trash and collected sediment when 60% of the sump depth has been filled or sediments are within 6 inches of the bottom of the outlet pipe. It should be apparent that the use of other BMPs, such as frequent sweeping of activity areas, covering activity areas, reducing activity occurrence, and containing run-off from activity areas will help reduce catch basin cleaning frequency, thus saving time and money. All businesses and agencies should set up maintenance schedules for all of their BMPs so coordinated BMP maintenance efforts results in reduced catch basin cleaning frequencies. Use of catch basin inserts such as filter socks, absorbent pillows, and filter baskets require an increased inspection frequency to prevent plugging and flooding. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 73 Chapter 4 4.9 Cover and Surround Activities 4.9.1 BMP S104: Cover the Activity with a Roof or Awning In many cases, a simple roof or awning will protect the activity from coming into contact with stormwater, and usually at a lower cost than a complete building. These structures require building permits to construct. Contact the City of Auburn Permit Center at 253-931-3090 to obtain permits. The area of the roof cover shall be sufficient to prevent any precipitation from reaching the covered materials. Provisions shall be made to prevent stormwater run-on into the covered area. The installation of sumps or sanitary sewer drains may also be necessary. Roof drains shall discharge outside and be directed away from the covered area. Examples of these types of structures are shown in Figure IV-4-19. Figure IV-4-19. Examples of Covered Activities S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 74 Chapter 4 4.9.2 BMP S105: Cover the Activity with an Anchored Tarp or Plastic Sheet Some activities, such as stockpiling of raw materials, can be effectively covered with a sturdy tarp or heavy plastic sheet made of impermeable material. Weights such as bricks, tires, or sandbags should be used to anchor the cover in place. Run-on shall be prevented from reaching the activity or material. Stormwater run-off from the cover shall be directed away from the stockpile and work zone, and if uncontaminated, directed to the stormwater collection system. The tarp must be inspected daily to ensure that no holes or gaps are present in the tarp coverage. An example of this type of cover is shown in Figure IV-4-20. Figure IV-4-20. Tarp Covering S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 75 Chapter 4 4.9.3 BMP S106: Pave the Activity Area and Slope to a Sump, Holding Tank, or Oil/Water Separator This BMP applies to several activities that cannot be covered effectively. It is particularly suited to activities with the potential for leaks and spills, but that otherwise do not generate excessive amounts of polluted runoff. The activity area shall be paved and sloped to a central collection point. A sump, holding tank, or oil/water separator (Figure IV-4-21) serves to provide spill containment until the liquids can be pumped out and properly disposed. The minimum volume for the sump shall be equivalent to the volume generated by the anticipated activity plus rain water. Sizing justification shall be included in design submittals. To prevent run-on, the area should be enclosed with a berm, curb, or dike as shown in Figure IV-4-23. Frequent inspections of the sump, holding tank, or oil/water separator are necessary. Inspections and maintenance shall be recorded in a log. Commercial services that pump sumps and holding tanks are listed in the Yellow Pages of the phone directory under Environmental and Ecological Services. Figure IV-4-21. Paved Area with Sump Drain S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 76 Chapter 4 4.9.4 BMP S107: Surround the Activity Area with a Curb, Dike, or Berm or Elevate the Activity This set of BMP options can be an effective means for prevention of stormwater run-on to an activity area. In addition, a curb, berm, or dike can be used for containment of spills in the activity area, or for containment of contaminated activity runoff. Generally, a containment BMP is most applicable to spill control situations; that is, sites where runoff is relatively clean, but occasional spills may occur. If a curb, berm, or dike is used for runoff containment, and other containment sizing regulations (such as fire codes, Environmental Protection Agency, or Department of Ecology restrictions) do not apply, the containment volume shall be 100% of the volume of the largest tank plus the volume of stormwater runoff from rain events up to the 25-year, 24-hour storm within the containment area is contained or 110% of the volume of the largest tank, whichever is greater. Impervious containment may consist of membrane lined soil enclosures, containment pallets, plastic pools, mortar mixing tubs, and water troughs. Regular inspections of the containment area and proper management of any collected stormwater is required. Development of a spill plan may be necessary for storage of liquids. See BMP A714. For permanent storage facilities see BMP A202, A401, A407, and A408. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 77 Chapter 4 Figure IV-4-22. Above-Ground Tank with Impervious Walls and Floor S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 78 Chapter 4 Figure IV-4-23. Containment Types S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 BMPs for Commercial and Industrial Activities Volume IV 5 79 Chapter 4 Figure IV-4-24. Standby Generator S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Regulations and Requirements Volume IV 5 80 Chapter 5 Chapter 5 Regulations and Requirements The information in this chapter is provided to aid in compliance with other Auburn and Washington State regulations, which may apply to a project, industry, or business in terms of protecting water quality. A listing of relevant regulations is provided but should be verified because of the continuing modification of statutes, regulations, and City ordinances. It is the applicant’s responsibility to obtain the current version of any ordinances, statutes, or regulations that apply to a specific project or activity. Copies of City ordinances are available at the City Clerk’s office in City Hall located at 25 West Main Street, 253-931-3039. 5.1 City of Auburn Codes and Ordinances The following summarizes Auburn City Code that applies to surface water and pollution control. The complete code may be found online at: http://www.auburnwa.gov/Home.asp 8.08 Solid Waste 12.20 Driveways 13 Water, Sewer and Public Utilities 13.48 Storm Drainage Utility 13.48.330 Off-site Improvements 14 Project Review 15.74 Land Clearing, Filling and Grading 16 Environment 16.08 Shoreline Regulation 16.10 Critical Areas 17 Subdivision 18 Zoning 5.2 State, Federal, and Other Regulations and Requirements 5.2.1 Washington State Department of Ecology Requirements for the Discharge of Process Wastewaters Directly to Surface Waters If a public sanitary sewer is not available, process wastewater may be discharged, after suitable treatment, to a surface water body like a lake or stream, or to a drainage field. If the discharge is to a surface water body, Ecology must approve the type and design of the treatment system, as well as the outfall design. If a septic tank and drain field are used for treatment, requirements of the Seattle-King County Health Department (SKCHD) or the Tacoma-Pierce County Health Department (TPCHD) will also apply. Contact SKCHD at 206-296-4932 or TPCHD TPCHD at 253-798-6470 for more information. Ecology’s requirements can be found at WAC Chapter 173.240. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Regulations and Requirements Volume IV 5 81 Chapter 5 5.2.2 Washington State Department of Ecology Requirements for Dangerous Waste Generators The state dangerous waste regulations (WAC Chapter 173-303) cover accumulation, storage, transportation, treatment, and disposal. Of interest to this manual is the temporary accumulation of waste until taken from the site to a permitted disposal site. Only portions of those regulations that apply to temporary storage are summarized here. Permitted Generators Businesses that generate 220 pounds or more of waste, either per batch or in the aggregate, over one month must comply with the storage specifications outlined below: Small-Quantity Waste Generators These are businesses that generate less than 220 pounds of dangerous waste per month or per batch (or 2.2 pounds of extremely hazardous waste). Small-quantity generators still fall under Ecology regulations to the extent that the materials materials must be properly stored on site until shipment. The wastes must be moved from the property whenever the accumulated quantity equals or exceeds 220 pounds or whenever the material has resided on site for 180 days. The waste must be disposed of at an approved facility. If the business is in compliance with these requirements, they are also considered solid waste generators, and are regulated by the local health departments. For technical assistance and site visits, contact the Tacoma-Pierce County Health Department at 253-798-6047 or the King County Hazardous Waste Management program at 206-296-4692. Regulations governing small-quantity generators are currently being reviewed to possibly raise the accumulation limit. Call the Hazardous Waste Line at 800-287-6429 for the most up-to-date information. Dangerous Waste Pollution Prevention Plans A recent state law established the requirement that generators of dangerous wastes in excess of 220 lbs/month (2,640 lbs/year) prepare a waste reduction plan, called a pollution prevention plan, not to be confused with the stormwater pollution prevention plan (see R.4). The required content of the plan is set forth in Pollution Prevention Planning -Guidance Manual, January 1992, Publication #91-2, for WAC Chapter 173-307. 5.2.3 Washington State Department of Ecology Stormwater NPDES Permit Requirements The Federal National Pollutant Discharge Elimination System (NPDES) program requires industries or industrial-type activities to obtain permits for stormwater discharge. Coverage under Ecology’s general permit for Stormwater Discharges Associated with Industrial Activities is required for each regulated facility. A business must obtain permit coverage if its primary activity falls under one of the categories listed in the permit or its fact sheet. The permit and fact sheet may be viewed on Ecology’s website at www.ecy.wa.gov/programs/wq/permits/index.html. The program requires the preparation of a stormwater pollution prevention plan (SWPPP). A NPDES permit is required for certain categories of industries and municipalities for discharge to surface water, or a storm drain that discharges to surface water or to surface water and groundwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Regulations and Requirements Volume IV 5 82 Chapter 5 5.2.4 Washington State Department of Ecology Requirements for Underground and Above Ground Storage Tanks Underground storage tanks (UST) that contain fuel and other petroleum products are regulated by the Department of Ecology under WAC Chapter 173-360 Underground Storage Tank Regulations. Above-ground storage tanks (ASTs) may also be regulated. Inquiries about businessspecific requirements and permitting for USTs and ASTs should be directed to the Department of Ecology, Northwest Regional Office at 425-649-7000. 5.2.5 U.S. Environmental Protection Agency and Ecology Emergency Spill Cleanup Requirements USEPA -Spill Prevention Control and Cleanup (SPCC) Plans (40 CFR 112) This federal regulation requires that owners or operators of facilities engaged in drilling, producing, gathering, storing, processing, refining, transferring, or consuming oil and oil products are required to have a spill prevention and control plan (SPCC), provided that the facility is not transportation related; and, that the aboveground storage of a single container is in excess of 660 gallons, or an aggregate capacity greater than 1,320 gallons, or a total below ground capacity in excess of 42,000 gallons. Department of Ecology Dangerous Wastes (WAC 173-303-350) The regulations state that generators must have a contingency plan that must include: 1. Actions taken in the event of a spill. 2. Descriptions of arrangements with local agencies. 3. Identification of the owner's emergency coordinator. 4. List of emergency equipment. 5. Evaluation plan for business personnel. See Federal Regulation 40 CFR 112 and WAC 173-303-350 for further information. 5.2.6 Washington State Department of Agriculture Pesticide Regulations Washington State pesticide laws are administered by the State's Department of Agriculture, under the Washington Pesticide Control Act (RCW Chapter 15.58), Washington Pesticide Application Action Action (RCW Chapter 17.21), and regulations in WAC Chapter 16.228. In Auburn, all pest control operators and fumigators are required to obtain certification from the appropriate County Health Department. Contact the Seattle-King County Health Department at 206-205-4394 or Tacoma-Pierce County Health Department’s Compliance Program at 253-798-6440 for more information. 5.2.7 Puget Sound Clean Air Agency Air Quality Regulations The Puget Sound region is under the jurisdiction of regional air quality authorities who in turn must function under Washington State and federal air quality regulations. The Puget Sound Clear Air Agency (PSCAA) is the regulatory agency for air quality in Auburn. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Quick Reference Phone Numbers Volume IV 5 83 Appendix A Appendix A Quick Reference Phone Numbers City of Auburn Storm Drainage Utility 253-931-3010 Permit Center 253-931-3090 Valley Regional Fire Authority 253-591-5740 Solid Waste Management Utility 253-931-3038 Household Hazardous Waste 253-931-3038 Recycling Services 253-931-3038 Environmental Protection Agency (EPA) -Region X 800-424-4372 IMEX (Industrial Materials Exchange) 206-296-4899 King County Wastewater Program (septic) 206-296-4932 Household Hazardous Waste 206-296-4692 Pest Control Operators 206-205-4394 Tacoma-Pierce County Health Department On-Site Sewage and Underground Storage Tanks 253-798-6470 Hazardous Waste Section 253-798-6047 Solid Waste 253-798-6047 Hazardous Waste Line 800-287-6429 Pest Control Operators and Fumigators 253-798-6470 University of Washington Center for Urban Water Resources 206-543-6272 Washington State Department of Agriculture 360-902-2010 877-301-4555 Washington State Department of Ecology 360-407-6000 Northwest Regional Office 425-649-7000 Dangerous/Hazardous Waste 360-407-6300 NPDES Stormwater or Wastewater Permits 360-407-6400 Spill Reporting 800-424-8802 Recycling 800-732-9253 Groundwater Quality and Protection 360-407-6400 Underground and Above Ground Storage Tanks 360-407-7170 Washington State University/Pierce County Cooperative Extension 253-798-7180 Puget Sound Clean Air Agency 800-552-3565 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recycling/Disposal of Vehicle Fluids Volume IV and Other Wastes 5 84 Appendix B Appendix B Recycling/Disposal of Vehicle Fluids and Other Wastes The information in this appendix was obtained from Ecology’s Hazardous Waste Program. For a copy of “Hazardous Waste Services Directory”, Publication #91-12S, Revised December 1994, call Ecology’s Hazardous Waste and Toxic Reduction Program at 360-407-6721. RECOMMENDED MANAGEMENT Antifreeze Store separately for resale. Separate ethylene glycol from propylene glycol for off-site recycling. If not recyclable, send to Treatment, Storage, and Disposal Facility (TSDF) for disposal. Batteries INTACT: Accumulate under cover prior to sale, deliver to recycler or, return to manufacturer. BROKEN: Accumulate acid from broken batteries in resistant containers with secondary containment. Send to TSDF for disposal. Brake fluid Accumulate in separate, marked, closed container. Do not mix with waste oil. Recycle. Fuel Store gasoline, and diesel separately for use or resale. Mixtures of diesel, gasoline, oil, and other fluids may not be recyclable and may require expensive disposal. Fuel filters Drain fluids for use as product. With approval of local landfill operator, dispose to dumpster, if needed. Oil filters Puncture the filter dome and drain it for 24 hours. Put oil drained from filters into a "USED OIL ONLY" container. Keep drained filters in a separate container marked "USED OIL FILTERS ONLY." Locate a scrap metal dealer who will pick up and recycle filters. With approval of local landfill operator, dispose of drained filters to dumpster. Paint Accumulate oil-based and water-based paints separately for use or resale. If not recyclable, send accumulations to TSDF for disposal. Power steering fluid Same as for used oils Shop towels/oily rags Use cloth towels that can be laundered and reused. Accumulate used shop towels in a closed container. Sign up with an industrial laundry service that can recycle your towels. Solvents Consider using less hazardous solvents or switching to a spray cabinet that does not use solvent. Accumulate solvents separately. Consider purchasing a solvent still and recycling solvent on site. Do not mix with used oil. Do not evaporate as a means of disposal. Transmission oil, differential and rear end fluids Accumulate in your "USED OIL ONLY" container. Arrange for pickup for off-site recycling. Used oils; including, crankcase oil, transmission oil, power steering fluid and differential/rear end oil Keep used oil in a separate container marked "USED OIL ONLY." Do not mix with brake fluid, or used antifreeze. Do not mix with any other waste if material will be burned for heating. Arrange for pickup for off-site recycling. Windshield washer fluid Accumulate separately for use or resale. Discharge to on-site sewage disposal, or, if acceptable by the local sewer authority, discharge to sanitary sewer. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Example of an Integrated Pest Volume IV Management Program (IPM) 5 85 Appendix C Appendix C Example of an Integrated Pest Management Program (IPM) Integrated Pest Management (IPM) is a natural, long-term, ecologically based systems approach to controlling pest populations. This system uses techniques either to reduce pest populations or maintain them at levels below those causing economic injury, or to manipulate the populations so that they are prevented from causing injury. The goals of IPM are to encourage optimal selective pesticide use (away from prophylactic, broad spectrum use), and to maximize natural controls to minimize the environmental side effects. A step-by-step comprehensive Integrated Pest Management (IPM) Program is provided below as a guide. Introduction This section provides a sound cultural approach to managing lawns and landscapes and minimizing runoff. Many homeowners or property managers will be able to implement most or all of this approach. Others will wish to hire these services out. For the do-it yourselfer, an array of resources are available to assist in the effort. Landscaping businesses, agricultural extensions, local agencies, master gardener programs, local nurseries, and the library can all provide assistance. Landscaping professionals (businesses) are particularly encouraged to practice IPM. Definition “Integrated pest management, or IPM, is an approach to pest control that uses regular monitoring to determine if and when treatments are needed, and employs physical, mechanical, cultural, and biological tactics to keep pest numbers low enough to prevent intolerable damage or annoyance. Least-toxic chemical controls are used as a last resort.” True IPM is a powerful approach that anticipates and prevents most problems through proper cultural practices and careful observation. Knowledge of the life cycles of the host plants and both beneficial and pest organisms is also important. The IPM section of this example is adapted from “Least Toxic Pest Management for Lawns” by Sheila Daar. Following the IPM process yields the information needed to minimize damage by weeds, diseases, and pests and to treat those problems with the least toxic approaches. The IPM Process Step 1. Correctly identify problem pests and understand their life cycle. Learn more about the pest. Observe it and pay attention to any damage that may be occurring. Learn about the life cycle. Many pests are only a problem during certain seasons, or can only be treated effectively in certain phases of the life cycle. Step 2. Establish tolerance thresholds for pests. Every landscape has a population of some pest insects, weeds, and diseases. This is good because it supports a population of beneficial species that keep pest numbers in check. Beneficial organisms may compete with, eat, or parasitize disease or pest organisms. Decide on the level of infestation S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Example of an Integrated Pest Volume IV Management Program (IPM) 5 86 Appendix C that must be exceeded before treatment needs to be considered. Pest populations under this threshold should be monitored but do not need treatment. For instance, European crane flies usually do not do serious damage to a lawn unless there are between 25 to 40 larvae per square foot feeding on the turf in February (in normal weather years). Also, most people consider a lawn healthy and well maintained even with up to 20% weed cover, so treatment, other than continuing good maintenance practices, is generally unnecessary. Step 3. Monitor to detect and prevent pest problems. Regular monitoring is a key practice to anticipate and prevent major pest outbreaks. It begins with a visual evaluation of the lawn or landscape's condition. Take a few minutes before mowing to walk around and look for problems. Keep a notebook, record when and where a problem occurs, then monitor for it at about the same time in future years. Specific monitoring techniques can be used in the appropriate season for some potential problem pests, such as European crane fly. Step 4. Modify the maintenance program to promote healthy plants and discourage pests. A healthy landscape is resistant to most pest problems. Lawn aeration and overseeding along with proper mowing height, fertilization, and irrigation will help the grass out-compete weeds. Correcting drainage problems and letting soil dry out between waterings in the summer may reduce the number of crane-fly larvae that survive. Step 5. If pests exceed the tolerance thresholds Use cultural, physical, mechanical, or biological controls first. If those prove insufficient, use the chemical controls described below that have the least non-target impact. When a pest outbreak strikes (or monitoring shows one is imminent), implement IPM then consider control options that are the least toxic, or have the least non-target impact. Here are two examples of an IPM approach: • Red thread disease is most likely under low nitrogen fertility conditions and most severe during slow growth conditions. Mow and bag the clippings to remove diseased blades. Fertilize lightly to help the grass recover, then begin grasscycling and change to fall fertilization with a slow-release or natural-organic fertilizer to provide an even supply of nutrients. Chemical fungicides are not recommended because red thread cannot kill the lawn. • Crane fly damage is most prevalent on lawns that stay wet in the winter and are irrigated in the summer. Correct the winter drainage and/or allow the soil to dry between irrigation cycles; larvae are susceptible to drying out, so these changes can reduce their numbers. It may also be possible to reduce crane fly larvae numbers by using a power de-thatcher on a cool, cloudy day when feeding is occurring close to the surface. Studies are being conducted using beneficial nematodes that parasitize the crane fly larvae; this type of treatment may eventually be a reasonable alternative. Only after trying suitable non-chemical control methods, or determining that the pest outbreak is causing too much serious damage, should chemical controls be considered. Study to determine what products are available and choose a product that is the least toxic and has the least non-target impact. Refer to the Operational BMPs for the use of Pesticides below for guidelines on choosing, storing, and using lawn and garden chemicals. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Example of an Integrated Pest Volume IV Management Program (IPM) 5 87 Appendix C Step 6. Evaluate and record the effectiveness of the control, and modify maintenance practices to support lawn or landscape recovery and prevent recurrence. Keep records! Note when, where, and what symptoms occurred, or when monitoring revealed a potential pest problem. Note what controls were applied and when, and the effectiveness of the control. Monitor next year for the same problems. Review your landscape maintenance and cultural practices to see if they can be modified to prevent or reduce the problem. A comprehensive IPM Program should also include the proper use of pesticides as a last resort, and vegetation/fertilizer management to eliminate or minimize the contamination of stormwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 88 Appendix D Appendix D Recommendations for Management of Street Wastes Introduction This appendix is a summary, taken from the June 1999 draft Ecology publication titled Recommendations for Management of Street Waste (Publication WQ 99-09). The guidance document addresses waste generated from stormwater maintenance activities such as street sweeping and the cleaning of catch basins and, to a limited extent, other stormwater conveyance and treatment facilities. Limited information is available on the characteristics of wastes from detention/retention ponds, bioswales, and similar stormwater treatment facilities. The recommendations provided here may be generally applicable to these facilities, with extra diligence given to waste characterization. These recommendations do not constitute rules or regulations, but are suggestions for street waste handling, reuse, and disposal supported by current regulations and the present state of knowledge of street waste constituents. The recommendations are intended to address the liquid and solid wastes collected during routine maintenance of stormwater catch basins, detention/retention ponds and ditches and similar stormwater treatment and conveyance structures, and street and parking lot sweeping. In addition to these recommendations, end users and other authorities may have their own requirements for street waste reuse and handling. "Street Wastes" include liquid and solid wastes collected during maintenance of stormwater catch basins and detention/retention ponds and ditches and similar stormwater treatment and conveyance structures, and solid wastes collected during street and parking lot sweeping. "Street Wastes," as defined here, does not include solids and liquids from street washing using detergents, cleaning of electrical vaults, vehicle wash sediment traps, restaurant grease traps, industrial process waste, sanitary sewage, mixed process, or combined sewage/stormwater wastes. Wastes from oil/water separators at sites that load fuel are not included as street waste. Street waste also does not include flood debris, land slide debris, and chip seal gravel. Street waste does not ordinarily classify as dangerous waste. The owner of the stormwater facility and/or collector of street waste is considered the waste generator and is responsible for determining whether or not the waste designates as dangerous waste. Sampling to date has shown that material from routine maintenance of streets and stormwater facilities does not classify as dangerous waste (See Table IV-D-7). However, it is possible that street waste from spill sites could classify as dangerous waste. Street waste from areas with exceptionally high average daily traffic counts may contain contaminants -such as heavy metals, total petroleum hydrocarbons (TPH), and carcinogenic polycyclic aromatic hydrocarbons (c-PAH) -at levels that limit reuse options. Street Waste Solids Street waste is solid waste. While street waste from normal street and highway maintenance is not dangerous waste, it is solid waste, as defined under The Solid Waste Management Act (Chapter 70.95 RCW) and under Solid Waste Handling Standards (Chapter 173-350 WAC). Under the Solid Waste Management Act, local health departments have primary jurisdiction over solid waste S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 89 Appendix D management. Street waste solids may contain contaminants at levels too high to allow unrestricted reuse. There are currently no specific references in the Solid Waste Handling Standards to facilities managing street waste solids. These facilities will typically fit under the section dealing with Piles Used for Storage and Treatment (Section 320 of the regulation). There are no specific references for reuse and disposal options for street wastes in the Solid Waste Handling Standards, although the Solid Waste Handling Standards do not apply to clean soils. In the rule, clean soils are defined as ‘soils that do not contain contaminants at concentrations which could degrade the quality of air, waters of the state, soils, or sediments; or pose a thereat to the health of humans or other living organisms’ (WAC 173-350-100). Whether or not a soil is a “clean soil” soil” depends primarily upon the level of contaminants and, to a lesser degree, on the background level of contaminants at a particular location and the exposure potential to humans or other living organisms. Therefore, both the soil and potential land application sites must be evaluated to determine if a soil is a clean soil. Local health departments should be contacted to determine if a street waste meets the definition of “clean soil” when it will be reused as a soil. There is no simple regulatory mechanism available to classify street waste solids as "clean" for uncontrolled reuse or disposal. Local health districts have historically used the Model Toxics Control Act Cleanup Regulation (MTCA) Method A residential soil cleanup levels to approximate "clean" and to make decisions on land application proposals. These regulations were amended in February 2001. The MTCA regulation is not intended to be directly applied to setting contaminant concentration levels for land application proposals. However, they may provide human health and environmental threat information and a useful framework for such decisions, when used in conjunction with other health and environmental considerations. The local health department should be contacted to determine local requirements for making this determination. Using the old MTCA regulations, many local health departments have set a criteria of 200 mg/kg Total Petroleum Hydrocarbons (TPH) for diesel and heavy fuel oils as a threshold level for clean soil. Using the new MTCA terrestrial ecological evaluation procedures, allowable TPH levels for land application could range from 200 – 460 mg/kg, depending on site characteristics and intended land use. Street waste sampling has historically yielded TPH values greater than 200 mg/kg for hydrocarbons in the diesel and heavy oil range. These values typically reflect interference from natural organic material and, to a lesser extent, relatively immobile petroleum hydrocarbons. The mobile hydrocarbons that are of concern for groundwater groundwater protection are generally not retained with street waste solids. Ecology's Manchester Lab has developed an analytical method to reduce the problem of natural organic material being included in the TPH analysis for diesel and heavier range hydrocarbons. This new method, called NWTPH-Dx, reduces the background interference associated with vegetative matter by as much as 85% to 95%. However, even with the new methodology, TPH test results for street waste may still be biased by the presence of natural vegetative material and may still exceed 200 mg/kg. Where the laboratory results report no ‘fingerprint’ or chromatographic match to known petroleum hydrocarbons, the soils should not be considered to be petroleum contaminated soils. Street waste solids frequently contain levels of carcinogenic PAHs (c-PAH) that make unrestricted use inappropriate. This is further complicated by analytical interference caused by organic matter that raises practical quantitation or reporting limits. To reduce the level of interference the use of US EPA Test Method 8270, incorporating the silica gel cleanup step, is recommended. The calculated c-PAH value can vary greatly depending upon how non-detect values are handled. The new MTCA Method A criterion for c-PAH is 0.1 mg/kg (the sum of all seven c-PAH parameters multiplied by the S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 90 Appendix D appropriate toxicity equivalency factor) for unrestricted land uses. The MTCA criteria for soil cleanup levels for industrial properties is 2.0 mg/kg. Following this guidance, most sites where street wastes could be reused as soil will be commercial or industrial sites, or sites where public exposure will be limited or prevented. Street waste treatment and storage facilities shall be permitted by the local health department as applicable. Under the Solid Waste Management Act, local health departments have primary jurisdiction over solid waste management Street waste handling facilities are subject to the requirements of the Solid Waste Handling Standards. The specific requirements will depend upon the manner in which the waste is managed. Most facilities will probably be permitted under the section dealing with Piles Used for Storage and Treatment (Section Section 320 of the regulation) For most facilities, permit requirements include a plan of operations, sampling, record keeping and reporting, inspections, and compliance with other state and local requirements. The plan of operation should include a procedure for characterization of the waste and appropriate reuse and disposal options, consistent with the recommendations in this document and applicable federal, state, and local requirements. A street waste site evaluation (see sample at end of this appendix) is suggested for all street waste as a method to identify spill sites or locations that are more polluted than normal. The disposal and reuse options listed below are based on characteristics of routine street waste and are not appropriate for more polluted wastes. The collector of street waste should evaluate it both for its potential to be classified as dangerous waste and to not meet end users requirements. Street waste that is suspected to be dangerous waste should not be collected with other street street waste. Material in catch basins with obvious contamination (unusual color, staining, corrosion, unusual odors, fumes, and oily sheen) should be left in place or segregated until tested. Testing should be based on probable contaminants. Street waste that is suspected to be dangerous waste should be collected and handled by someone experienced in handling dangerous waste. If potential dangerous waste must be collected because of emergency conditions, or if the waste becomes suspect after it is collected, it should be handled and stored separately until a determination as to proper disposal is made. Street waste treatment and storage facilities should have separate "hot load" storage areas for such waste. Dangerous Waste includes street waste known and suspected to be dangerous waste. This waste must be handled following the Dangerous Waste Regulations (Chapter 173-303 WAC) unless testing determines it is not dangerous waste. Spills should be handled by trained specialists. Public works maintenance crews and private operators conducting street sweeping or cleaning catch basins should have written policies and procedures for dealing with spills or suspected spill materials. Emergency Spill Response telephone numbers should be immediately available as part of these operating policies and procedures. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 91 Appendix D The end recipient of street waste must be informed of its source and may have additional requirements for its use or testing that are not listed here. This document is based primarily on average street waste's chemical constituents and their potential effect on human health and the environment. There are physical constituents (for example, broken glass or hypodermic needles) or characteristics (for example, fine grain size) that could also limit reuse options. Additional treatment such as drying, sorting, or screening may also be required, depending on the needs and requirements of the end user. Street waste treatment and storage facilities owned or operated by governmental agencies should be made available to private waste collectors and other governmental agencies on a cost recovery basis. Proper street waste collection and disposal reduces the amount of of waste released to the environment. The operators of street waste facilities should restrict the use of their facilities to certified and/or licensed waste collectors who meet their training and liability requirements. The use of street waste solids under this guidance should not lead to designation as a hazardous waste site, requiring cleanup under MTCA. Exceeding MTCA Method A unrestricted land use cleanup levels in street waste and products made from street waste, does not automatically make the site where street waste is reused a cleanup site. A site is reportable only if "-a release poses a threat to human health or the environment-" (Model Toxic Control Act). The reuse options proposed below are designed to meet the condition of not posing a threat to human health or the environment. Testing of street waste solids will generally be required as part of a plan of operation that includes procedures for characterization of the waste. Testing frequency, numbers of samples, parameters to be analyzed, and contaminant limit criteria should all be provided as part of an approved plan of operation. Table IV-D-5 and Table IV-D-6 provide some recommended parameters and sampling frequencies for piles of street waste solids from routine street maintenance. These are provided as guidance only and are intended to assist the utility and the local health department in determining appropriate requirements. Sampling requirements may be modified, over time, based on accumulated data. When the material is from a street waste facility or an area that has never been characterized by testing, the test should be conducted on a representative sample before co-mingling with other material. Testing in these instances would be to demonstrate that the waste does not designate as dangerous waste and to characterize the waste for reuse. At a minimum, the parameters in Table IV-D-5 are recommended for these cases. Note that it will generally not be necessary to conduct Toxic Characteristic Leaching Procedure (TCLP) analyses when the observed values do not exceed the recommended values in Table IV-D-5. Table IV-D-7 illustrates some observed relationships between total metals and TCLP metals values. For further information on testing methods and sampling plans, refer to: • SW 846 (US EPA, Office of Solid Waste, Test Methods for Evaluating Solid Wastes, 3rd Edition) and • Standard Methods for the Examination of Water and Wastewater (American Public Health Association, et al., 18th Edition, 1992) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 92 Appendix D For street waste not exceeding the suggested maximum values in Table IV-D-5 the following street waste solids reuse and disposal options are recommended: • Street sweepings that consist primarily of leaves, pine needles and branches, and grass cuttings from mowing grassy swales can be composted. Litter and other foreign material must be removed prior to composting or the composting facility must provide for such removal as part of the process. The screened trash is solid waste and must be disposed of at an appropriate solid waste handling facility. • Coarse sand screened from street sweeping after recent road sanding may be reused for street sanding, provided there is no obvious contamination from spills. The screened trash is solid waste and must be disposed of at an appropriate solid waste handling facility. • Roadside ditch cleanings, not contaminated by a spill or other release and not associated with a stormwater treatment system such as a bioswale, may be screened to remove litter and separated into soil and vegetative matter (leaves, grass, needles, branches, etc.). The soils from these activities are not generally regulated as solid waste. Ditching material that may be contaminated must be stored, tested, and handled in the same manner as other street waste solids. It is the generator’s responsibility to visually inspect and otherwise determine whether the materials may be contaminated. • Construction street waste -solids collected from sweeping or in stormwater treatment systems at active construction sites -may be placed back onto the site that generated it, or managed by one of the methods listed below, provided that it has not been contaminated as a result of a spill. For concrete handling at construction site, refer to BMP C151 in Volume II. • Screened street waste soils may be used as feedstock materials for topsoil operations. This option should be reserved for street waste soils with very low levels of contaminants. Diluting street waste soils with clean soils or composted material must not be used as a substitute for treatment or disposal. There may be physical contaminants (for example, glass, metal, nails, etc.) in street waste that cannot be entirely screened from the waste. Where present, these contaminants in street waste could preclude its use as feedstock material for topsoil operations. • Fill in parks, play fields, golf courses, and other recreational settings where direct exposure by the public is limited or prevented. One way to prevent or limit direct exposure is to cover the fill with sod, grass, or other capping material to reduce the risk of soil being ingested. The level of contaminants in the street waste must be evaluated to ensure that the soils meet the definition of clean soils when used in this manner. • Fill in commercial and industrial areas, including soil or top dressing for use at industrial sites, roadway medians, airport infields, and similar sites where there is limited direct human contact with the soil and the soils will be stabilized with vegetation or other means. The level of contaminants in the street waste must be S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 93 Appendix D evaluated to ensure that the soils meet the definition of clean soils when used in this manner. • Top dressing on roadway slopes, road or parking lot construction material, road or parking lot subgrade, or other road fill. The level of contaminants in the street waste must be evaluated to ensure that the soils meet the definition of clean soils when used in this manner. • Daily cover or fill in a permitted municipal solid waste landfill, provided the street waste solids have been dewatered. Street waste solids may be acceptable as final cover during a landfill closure. The local health department and landfill operator should be consulted to determine conditions of acceptance. • Treatment at a permitted contaminated soil treatment facility. • Recycling through incorporation into a manufactured product, such as Portland cement, prefab concrete, or asphalt. The facility operator should be consulted to determine conditions of acceptance. • Other end uses as approved by the local health department. • Disposal at an appropriate solid waste handling facility. For street waste that exceeds the suggested maximum values in Table IV-D-5, the following street waste solids reuse and disposal options are recommended: • Treatment at a permitted contaminated soil treatment facility. • Recycling through incorporation into a manufactured product, such as Portland cement, prefab concrete, or asphalt. The facility operator should be consulted to determine conditions of acceptance. • Other end uses as approved by the local health department. • Disposal at an appropriate solid waste handling facility. Street Waste Liquids Street waste collection should emphasize solids in preference to liquids. Street waste solids are the principal objective in street waste collection and are substantially easier to store and treat than liquids. Street waste liquids require treatment and/or must follow location limitations before their discharge. Street waste liquids usually contain high amounts of suspended and total solids and adsorbed metals. Treatment requirements depend on the discharge location. Discharges to sanitary sewer and storm sewer systems must be approved by the entity responsible for operation and maintenance of the system. Ecology will not generally require waste discharge permits for discharge of stormwater decant to sanitary sewers or to stormwater treatment BMPs constructed and maintained in accordance with Ecology’s Stormwater Management Manual for Western Washington. (See Volume V for further detail). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 94 Appendix D The following disposal options are recommended, in order of preference, for catch basin decant liquid and for water removed from stormwater treatment facilities. Under the Municipal General Permit, municipalities are required to use this guidance in determining appropriate means of dealing with street wastes from stormwater maintenance activities. Ecology Northwest Regional Office water quality staff can help you with treatment standards and permit requirements for your particular situation. Discharge of catch basin decant liquids to a municipal sanitary sewer connected to a Public Owned Treatment Works (POTW) is the preferred disposal option. Discharge to a municipal sanitary sewer requires the approval of the sewer authority. Street waste liquids discharged to a POTW may be treated at a combined street waste liquid and solid facility (decant facility) or or at separate liquids only facilities. These liquid only facilities may consist of modified type 2 catch basins (with a flow restrictor or oil/water separator) or water quality vaults, strategically located through the sanitary collection system. These should provide 24 hour detention for the expected volumes and should be constructed and operated to ensure that the decant discharge does not re-suspend sediments. Sewer authorities should require periodic sampling and decant facility operators should test their waste effluent on a regular basis, but street waste decant liquid should meet the most restrictive local limits with 24 hours of undisturbed gravity settling. Overnight settling is more practical and will likely meet most local pretreatment requirements. (See Table IV-D-10 for typical catch basin decant values from King County’s decant facility at Renton). Discharge of stormwater runoff into sanitary sewers requires a Metro-King County Discharge permit to avoid hydraulic overloads and treatment performance problems. Stormwater removed from catch basins and stormwater treatment wetvaults may be discharged into a Basic or Enhanced Stormwater Treatment BMP. Decant liquid collected from cleaning catch basins and stormwater treatment wetvaults may be discharged back into the storm sewer system under the following conditions: • The preferred disposal option of discharge to sanitary sewer is not reasonably available, and • The discharge is to a Basic or Enhanced Stormwater Treatment Facility (See Volume V), and • The storm sewer system owner/operator has granted approval and has determined that the treatment facility will accommodate the increased loading. Pretreatment may be required to protect the treatment BMP. Reasonable availability will be determined by the stormwater utility and by the circumstances including such factors as distance, time of travel, load restrictions, and capacity of the stormwater treatment facility. Auburn may choose not to allow discharge back to the storm sewer system. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 95 Appendix D Discharging back into the storm sewer is an acceptable option, under certain conditions: • Other practical means are not reasonably available, and • Pretreatment is provided by discharging to a modified type 2 catch basin (with a flow restrictor or oil/water separator) or water quality vault, and • The discharge is upstream of a basic or enhanced stormwater treatment BMP, and • The storm sewer system owner/operator has granted approval. Other practical means include the use of decanting facilities and field decant sites that discharge to sanitary sewers or discharge to an approved stormwater treatment BMP. Limited field testing of flocculent aids has been conducted. While the use of flocculent aids is promising, sufficient testing has not been conducted to allow approval of any specific product or process. In general, the following conditions must be met for flocculent use to be approved: • The flocculent must be non-toxic under circumstances of use and approved for use by the Department of Ecology. • The decant must be discharged to an approved basic or enhanced stormwater treatment BMP, with sufficient capacity and appropriate design to handle the anticipated volume and pollutant loading. • The discharge must be approved by the storm sewer system owner/operator. Water removed from stormwater ponds, vaults, and oversized catch basins may be returned to storm sewer system. Stormwater ponds, vaults, and oversized catch basins contain substantial amounts of liquid, which hampers the collection of solids and poses problems if the removed waste must be hauled away from the site. Water removed from these facilities may be discharged back into the pond, vault, or catch basin provided: • Clear water removed from a stormwater treatment structure may be discharged directly to a downgradient cell of a treatment pond or into the storm sewer system. • Turbid water may be be discharged back into the structure it was removed from if: o The removed water has been stored in a clean container (eductor truck, Baker tank, or other appropriate container used specifically for handling stormwater or clean water) and o There will be no discharge from the treatment structure for at least 24 hours. • The discharge must be approved by the storm sewer system owner/operator. Vegetation management and structural integrity concerns sometimes require that the ponds be refilled as soon after solids removal as possible. For ponds and other systems relying on biological processes for waste treatment, it is often preferable to reuse at least some portion of the removed water. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 96 Appendix D Site Evaluation A site evaluation is suggested as method to identify spill sites or locations that are more polluted than normal. The site evaluation will aid in determining if waste should be handled as dangerous waste and in determining what to test for if dangerous waste is suspected. The site evaluation will also help to determine if the waste does not meet the requirements of the end users. There are three steps to a site evaluation: 1. A historical review of the site for spills, previous contamination, and nearby toxic cleanup sites and dangerous waste and materials. The historical review will be easier if done on an area wide basis prior to scheduling any waste collection. The historical review should be more thorough for operators who never collected waste at a site before. At a minimum, the historical review should include operator knowledge of the area's collection history or records kept from previous waste collections. Private operators should ask the owner of the site for records of previous contamination and the timing of the most recent cleaning. Ecology’s Hazardous Substance Information Office maintains a Toxic Release Inventory and a “Facility Site” web page, tracking more than 15,000 sites. This information is available through the Internet at http://www.wa.gov/ecology/iss/fsweb/fshome.html or by calling a toll-free telephone number (800-633-7585). The web page allows anyone with web-access to search for facility information by address, facility name, town, zip code, and SIC code, etc. It lists why the Department of Ecology is tracking each one (NPDES, TSCA, RCRA, Clean Air Act, etc.), as well as who to call within Ecology to find out more about the given facility. 2. An area visual inspection for potential contaminant sources such as a past fire, leaking tanks and electrical transformers, and surface stains. The area around the site should be evaluated for contaminant sources prior to collection of the waste. The area visual inspection may be done either as part of multiple or as single site inspections. If a potential contaminant source is found, the waste collection should be delayed until the potential contaminant is assessed. A second portion of the area visual inspection is a subjective good housekeeping evaluation of the area. Locations with poor housekeeping commonly cut corners in less obvious places and should be inspected in greater detail for illegal dumping and other contamination spreading practices. 3. A waste and container inspection before and during collection. The inspection of the waste and catch basin or vault is the last and perhaps most critical step in the site evaluation. For example, if the stormwater facility has an unusual color in or around it, then there is a strong possibility that something could have been dumped into it. Some colors to be particularly wary of are yellow-green from antifreeze dumping and black and/or rainbow sheen from oil and/or grease dumping. In addition, if any staining or corrosion is observed, then a solvent may have been dumped. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 97 Appendix D Fumes are also good indicators of potential dangerous conditions or dangerous waste. Deliberate smelling of catch basins should be avoided for worker safety, but suspicious odors may be encountered from catch basins thought to be safe. Some suspicious odors are rotten eggs (hydrogen sulfide is present), gasoline or diesel fumes, or solvent odors. If unusual odors are noted, contact a dangerous waste inspector before cleaning the basin. Finally, operator experience is the best guide to avoid collection of contaminated waste. Table IV-D-2. Typical TPH Levels in Street Sweeping and Catch Basin Solids Reference Street Sweeping (mg/kg) Catch Basin Solid (mg/kg) Snohomish County 1 (Landau 1995) 390 – 4300 King County (1) (Herrera 1995) 123 – 11049 (Median 1036) Snohomish County & Selected Cities 1 (W & H Pacific, 1993) 163 -1500 (Median 760) 163 – 1562 (Median 760) City of Portland 2 (Bresch) MDL – 1830 (Median – 208) Oregon1 (Collins; ODOT 1998) Oregon 3 (Collins; ODOT 1998) 1600 – 2380 98 -125 1 Method WTPH 418.1; does not incorporate new methods to reduce background interference due to vegetative material 2 Method NWTPH-Dx 3 Method WTPH – HCID S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 98 Appendix D Table IV-D-3. Typical c-PAH Values in Street Waste Solids and Related Materials Sample Source City of Everett WSDOT Analyte Street Sweepings Soil 3-Way Topsoil Vactor Solids Leaf & Sand Sweepings – Fresh Sweepings Weathered Benzo(a)anthracene 0.1U 0.076U 0.074U 0.21 0.45 0.56 0.40 Chrysene 0.14 0.09 0.074U 0.32 0.53 0.35 0.35 Benzo(b)fluoranthene 0.11 0.076U 0.074U 0.27 0.52 0.43 0.51 Benzo(k)fluoranthene 0.13 0.076U 0.074U 0.25 0.38 0.39 0.40 Benzo(a)pyrene 0.13 0.076U 0.074U 0.26 0.5 0.41 0.33U Indeno(1,2,3-cd)pyrene 0.1U 0.076U 0.074U 0.19 0.39 NR NR Dibenzo(a,h)anthracene 0.1U 0.076U 0.074U 0.081 0.12 0.39 0.33U Revised MTCA Benzo(a)pyrene [ND=PQL] 0.215 0.134 0.134 0.388 0.727 0.708 0.597 Benzo(a)pyrene [ND=1/2 PQL] 0.185 0.069 0.067 0.388 0.727 0.708 0.366 Benzo(a)pyrene [See * below] 0.185 0.069 0 0.388 0.727 0.708 0.366 Benzo(a)pyrene [ND=0] 0.155 0.001 0 0.388 0.727 0.708 0.135 *If the analyte was not detected for any PAH, then ND=0; If analyte was detected in at least 1 PAH, then ND=1/2PQL; If the average concentration (using ND=1/2 PQL) is greater than the maximum detected value, then ND=Maximum value. The new Method A soil cleanup level for unrestricted land use is 0.1 mg/Kg for BAP. (WAC 173-340-900, Table 740-1) The new Method A soil cleanup level for industrial properties is 2 mg/Kg for BAP. (WAC 173-340-900, Table 745-1) Table IV-D-4. Typical Metals Concentrations in Catch Basin Sediments PARAMETER Ecology 1993 Thurston 1993 King County 1995 King County 1995 METALS; TOTAL (mg/kg) (Min – Max) (Min – Max) (Min -Max) Mean As <3 --24 .39 --5.4 4 – 56 0.250 Cd 0.5 --2.0 < 0.22 --4.9 0.2 – 5.0 0.5 Cr 19 --241 5.9 --71 13 -100 25.8 Cu 18 --560 25 --110 12 -730 29 Pb 24 --194 42 --640 4 – 850 80 Ni 33 --86 23 --51 14 – 41 23 Zn 90 --558 97 --580 50 – 2000 130 Hg .04 --.16 .024 --.193 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 5 99 Appendix D Table IV-D-5. Recommended Parameters & Suggested Values for Determining Reuse & Disposal Options Parameter Suggested Maximum Value Arsenic, Total 20.0 mg/kg (a) Cadmium, Total 2.0 mg/kg (b) Chromium, Total 42 mg/kg (c) Lead, total 250 mg/kg (d) Nickel 100 mg/kg (e) Zinc 270 mg/kg (e) Mercury (Inorganic) 2.0 mg/kg (f) PAHs (Carcinogenic) 0.1 – 2.0 mg/kg (see Note at (g) below) TPH (Heavy Fuel Oil) 200 -460 mg/kg (see Note at (h) below) TPH (Diesel) 200 – 460 mg/kg (see Note at (h) below) TPH (Gasoline) 100 mg/kg (i) Benzene 0.03 mg/kg (i) Ethylbenzene 6 mg/kg (i) Toluene 7 mg/kg (i) Xylenes (Total) 9 mg/kg (i) a Arsenic: from MTCA Method A -Table 740-1: Soil cleanup levels for unrestricted land uses b Cadmium: from MTCA Method A – Table 740-1: Soil cleanup levels for unrestricted land uses. c Chromium; from MTCA Method A -Table 740-1: Soil cleanup levels for unrestricted land uses d Lead; from MTCA Method A – Table 740-1: Soil cleanup levels for unrestricted land uses e Nickel and Zinc; from MTCA Table 749-2: Protection of Terrestrial Plants and Animals f Mercury; from MTCA Method A – Table 740-1: Soil cleanup levels for unrestricted land uses g PAH-Carcinogenic; from MTCA Method A – Table 740-1: Soil cleanup levels for unrestricted land uses and Table 745-1, industrial properties, based on cancer risk via direct contact with contaminated soil (ingestion of soil) in residential land use situations and commercial/industrial land uses. Note: The local health department may permit higher levels as part of a Plan of Operation, where they determine that the proposed end use poses little risk of direct human contact or ingestion of soil. h TPH: from MTCA Tables 749-2 & 749-3: Protection of Terrestrial Plants and Animals. Values up to 460 mg/kg may be acceptable where the soils are capped or covered to reduce or prevent exposure to terrestrial plants and animals. Where the laboratory results report no ‘fingerprint’ or chromatographic match to known petroleum hydrocarbons, the soils will not be considered to be petroleum contaminated soils. i BETX; from MTCA Method A -Table 740-1: Soil cleanup levels for unrestricted land uses. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 6 00 Appendix D Table IV-D-6. Recommended Sampling Frequency for Street Waste Solids Cubic Yards of Solids Minimum Number of Samples 0 – 100 3 101 – 500 5 501 – 1000 7 1001 – 2000 10 >2000 10 + 1 for each additional 500 cubic yards *Modified from Ecology’s Interim Compost Guidelines Table IV-D-7. Pollutants in Catch Basin Solids – Comparison to Dangerous Waste Criteria PARAMETER Range of Values in Catch Basin Waste Range of Values in Catch Basin Waste Dangerous Waste Criteria METALS Total Metals (mg/kg) TCLP Metals (mg/kg) TCLP values (mg/l) Arsenic <3 – 56 < .02 -0 .5 5.0 Cadmium <.22 – 5 .0002 -.03 1.0 Chromium 5.9 -241 .0025 -.1 5.0 Copper 12 -730 .002 --.88 none Lead 4 -850 .015 --3.8 5.0 Nickel 23 -86 < .01 --.36 none Zinc 50 -2000 .04 --6.7 none Mercury .02 -.19 .0001 --.0002 0.2 * Data from Thurston County (Thurston County 1993), King County (Herrera 1995) and Ecology (Serdar; Ecology 1993). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 6 01 Appendix D Table IV-D-8. Typical Catch Basin Decant Values Compared to Surface Water Quality Criteria PARAMETER State Surface Water Quality Criteria Range of Values Reported Range of Values Reported METALS Freshwater Acute (ug/l – dissolved metals) Freshwater Chronic (ug/l – dissolved metals) Total Metals (ug/l) Dissolved Metals (ug/l) Arsenic 360 190 100 – 43000 60 -100 Cadmium* 2.73 0.84 64 -2400 2 -5 Chromium (total) 13 --90000 3 -6 Chromium (III)* 435 141 Chromium (VI) 0.5 10 Copper* 13.04 8.92 81 --200000 3 -66 Lead* 47.3 1.85 255 --230000 1 -50 Nickel* 1114 124 40 --330 20 -80 Zinc* 90.1 82.3 401 --440000 1900 -61000 Mercury 2.10 .012 0.5 --21.9 *Hardness dependent; hardness assumed to be 75 mg/l Table IV-D-9. Typical Values for Conventional Pollutants in Catch Basin Decant PARAMETER Ecology 1993 (Min -Max) King County 1995 (Min -Max) Values as mg/l; except where stated Mean Mean PH 6.94 6.18 -7.98 8 6.18 -11.25 Conductivity (umhos/cm) 364 184 -1110 480 129 -10,100 Hardness (mg/l CaCO3) 234 73 -762 Fecal Coliform (MPN/100 ml) 3000 BOD 151 28 -1250 COD 900 120 -26,900 Oil & Grease 11 7.0 -40 471 15 -6242 TOC 136 49 -7880 3670 203 -30,185 Total Solids 1930 586 -70,400 Total Dissolved Solids 212 95 -550 Total Suspended Solids 2960 265 -111,000 Settleable Solids (ml/l/hr) 27 2 -234 57 1 -740 Turbidity (ntu) 1000 55 -52,000 4673 43 -78,000 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Recommendations for Management Volume IV of Street Wastes 6 02 Appendix D Table IV-D-10. Catch Basin Decant Values Following Settling* Parameter; Total Metals in mg/l Portland – Inverness Site Min -Max King County -Renton Min -Max METRO Pretreatment Discharge Limits Arsenic .0027 .015 < MDL – 0.12 4 Cadmium .0009 -.0150 < MDL – 0.11 0.6 Chromium .0046 -.0980 .017 – .189 5 Copper .015 -.8600 .0501 – .408 8 Lead .050 – 6.60 .152 – 2.83 4 Nickel .0052 -.10 .056 -.187 5 Silver .0003 -.010 < MDL 3 Zinc .130 – 1.90 .152 – 3.10 10 Settleable Solids; ml/L No Data .02 -2 7 Nonpolar FOG 5.7 -25 5 -22 100 Ph (std) 6.1 – 7.2 6.74 – 8.26 5.0 -12.0 TSS 2.8 -1310 Recorded Total Monthly Flow; Gallons Data not available 31,850 -111,050 Recorded Max. Daily Flow; Gallons Data not available 4,500 -18,600 25,000 GPD Calculated Average Daily Flow; GPD Data not available 1517 -5428 * Data from King County’s Renton Facility (data from 1998 – 1999) and the City of Portland’s Inverness Site (data from 1999 – 2001); detention times not provided Volume V i Table of Contents Volume V – Water Quality Treatment BMPs Table of Contents Purpose of this Volume ......................................................................................... ..........................603 Content and Organization of this Volume .......................................................................................603 Chapter 1 Treatment Facility Selection Process .............................................................604 1.1 Step-by-Step Selection Process for Treatment Facilities......................................................604 Chapter 2 Treatment Facility Menus.................................................................................610 2.1 Oil Control Menu............................................................ ........................................................610 2.1.1 Performance Goal............................................................................................................ 610 2.1.2 Options............................................................................................................................ 610 2.1.3 Application on the Project Site................ ......................................................................... 611 2.2 Phosphorus Treatment Menu............................................................................................ ....611 2.2.1 Performance Goal............................................................................................................ 611 2.2.2 Options........................................... ................................................................................. 611 2.3 Enhanced Treatment Menu...................................................................................... .............612 2.3.1 Performance Goal............................................................................................................ 612 2.3.2 Options.................................. .......................................................................................... 612 2.4 Basic Treatment Menu ............................................................................... ...........................613 2.4.1 Performance Goal............................................................................................................ 613 2.4.2 Options.................... ........................................................................................................ 614 Chapter 3 General Requirements for Stormwater Facilities ................................. ..........615 3.1 Design Flow Volume and Flow Rate .....................................................................................615 3.1.1 Water Quality Design Flow Volume..................... ............................................................ 615 3.1.2 Water Quality Design Flow Rate ..................................................................................... 616 3.1.3 Flows Requiring Treatment.............................................................................................. 616 3.2 Sequence of Facilities ...................................... .....................................................................617 3.3 Setbacks, Slopes, and Embankments...................................................................................618 3.3.1 Setbacks .......................................................................................................................... 618 3.3.2 Side Slopes and Embankments ....................... ............................................................... 619 3.4 Facility Liners................................................................................................................ .........620 3.4.1 General Design Criteria ................................................................................................... 620 3.4.2 Design Criteria for Treatment Liners ............................................................................... 622 3.4.3 Design Criteria for Low Permeability Liner Options.................................................... ..... 622 Volume V ii Table of Contents 3.4.3.1 Compacted Till Liners............................................................................................622 3.4.3.2 Clay Liners ........................ ....................................................................................623 3.4.3.3 Geomembrane Liners..................................................................................... .......623 3.4.3.4 Concrete Liners .....................................................................................................624 3.5 Hydraulic Structures .................................. ............................................................................624 3.5.1 Flow Splitter Designs ........................................................................................... ............ 624 3.5.1.1 General Design Criteria.........................................................................................624 3.5.1.2 Materials......................................... .......................................................................624 3.5.2 Flow Spreading Options ............................................................................................... ... 627 3.5.2.1 General Design Criteria.........................................................................................627 Chapter 4 Pretreatment ............................................ .........................................................632 4.1 Purpose .............................................................................................................................. ..632 4.2 Application .............................................................................................................................632 4.3 BMPs for Pretreatment ...................... ....................................................................................632 4.3.1 BMP T610 Presettling Basin............................................................................... ............. 632 4.3.1.1 Purpose and Definition..........................................................................................632 4.3.1.2 Application and Limitations ..................... ..............................................................632 4.3.1.3 Design Criteria.......................................................................................................632 4.3.1.4 Site Constraints and Setback Requirements ........................................................633 Chapter 5 Infiltration and Bio-infiltration Treatment Facilities ........................ ...............634 5.1 Purpose ................................................................................................................................634 5.2 Application .................... .........................................................................................................634 5.3 Site Suitability ..................................................................... ...................................................634 5.3.1 Setback Criteria (SSC-1) ................................................................................................. 635 5.3.2 Groundwater Protection Areas (SSC-2) .......................................................................... 635 5.3.3 High Vehicle Traffic Areas (SSC-3) ................................ ................................................. 635 5.3.4 Soil Infiltration Rate/Drawdown Time for Treatment (SSC-4).......................................... 636 5.3.4.1 Infiltration Rates: Short-term and Long-term.........................................................636 5.3.4.2 Drawdown Time ..................................................................................... ...............636 5.3.5 Depth to Bedrock, Water Table, or Impermeable Layer (SSC-5).................................... 636 5.3.6 Soil Physical and Chemical Suitability for Treatment (SSC-6) ........................................ 637 5.3.7 Seepage Analysis and Control (SSC-7) .......................................................................... 637 5.3.8 Cold Climate and Impact of Roadway Deicers (SSC-8) .................................................. 637 5.3.9 Verification Testing of the Completed Facility ............................................. .................... 637 5.4 Site Characterization .............................................................................................................638 5.4.1 Field Methods used to Determine Subsurface Characterization..................................... 638 5.4.1.1 Test Holes or Pits ..................................................................................... .............638 5.4.1.2 Infiltration Rate Determination...............................................................................639 5.4.1.3 Infiltration Receptor .............................. .................................................................639 Volume V iii Table of Contents 5.4.2 Design Infiltration Rate Determination............................................................................. 640 5.4.2.1 Three Methods for Determining Long-term Infiltration Rate for Sizing the Infiltration Basin, Trench, or Swale ........................................................................................640 5.4.2.2 General Sizing Criteria ..........................................................................................642 5.4.2.3 General Design Criteria.......................................... ...............................................643 5.4.2.4 General Construction Criteria................................................................................643 5.4.2.5 Maintenance Criteria .............................................................................................644 5.4.2.6 Verification of Performance.......................................................... .........................644 5.5 BMPs for Infiltration and Bio-infiltration Treatment................................................................644 5.5.1 BMP T710 Infiltration Basins ........................................................................................... 645 5.5.1.1 Description ................................................................................... .........................645 5.5.1.2 Design Criteria Specific for Basins........................................................................645 5.5.1.3 Maintenance Criteria for Basins ............................................................................645 5.5.2 BMP T720 Infiltration Trenches .................................................................................. ..... 646 5.5.2.1 Description ............................................................................................................646 5.5.2.2 Design Criteria.................................. .....................................................................646 5.5.2.3 Construction Criteria..............................................................................................646 5.5.2.4 Maintenance Criteria .............................................................................................647 5.5.3 BMP T730 Bio-infiltration Swale ................................... ................................................... 648 5.5.3.1 Description ............................................................................................................648 5.5.3.2 Additional Design Criteria Specific for Bio-infiltration Swales ...............................648 Chapter 6 Sand Filtration Treatment Facilities ............................................. ...................650 6.1 Purpose ................................................................................................................................650 6.2 Description................. ...........................................................................................................650 6.3 Applications and Limitations ....................................................... ...........................................656 6.4 Site Suitability ........................................................................................................................656 6.5 Design Criteria.......................................................................................................................656 6.5.1 Objective.......................................... .................................................................. ............. 656 6.5.2 Sand Filter Sizing............................................................................................................. 656 6.6 Construction Criteria.................. ............................................................................................659 6.7 Maintenance Criteria .............................................................................. ...............................659 6.7.1 BMP T810 Sand Filter Vault ............................................................................................ 661 6.7.1.1 Description: (Figure V-6-13 and Figure V-6-14)....................................................661 6.7.1.2 Applications and Limitations.......................................................................... ........661 6.7.1.3 Additional Design Criteria for Vaults .....................................................................661 6.7.2 BMP T820 Linear Sand Filter .................................. ....................................................... 664 6.7.2.1 Description ............................................................................................................664 6.7.2.2 Application and Limitations ...................................................................................664 6.7.2.3 Additional Design Criteria for Linear Sand Filters .................................................664 Chapter 7 Biofiltration Treatment Facilities .....................................................................666 7.1 Purpose ................................................................................................................................666 7.2 Applications .................................................. .........................................................................666 Volume V iv Table of Contents 7.3 Site Suitability ........................................................................................................................666 7.4 Best Management Practices..................................................................................................666 7.4.1 BMP T910 Basic Biofiltration Swale .................................... ............................................ 667 7.4.1.1 Description: ...........................................................................................................667 7.4.1.2 Design Criteria:......................................................................................................667 7.4.1.3 Bypass Guidance ..................................................... .............................................671 7.4.1.4 Sizing Procedure for Biofiltration Swales ..............................................................671 7.4.1.5 Soil Criteria............. ...............................................................................................678 7.4.1.6 Vegetation Criteria......................................................................... ........................679 7.4.1.7 Construction Criteria..............................................................................................679 7.4.1.8 Maintenance Criteria .............................................................................................679 7.4.2 BMP T920 Wet Biofiltration Swale................................................................ ................... 683 7.4.2.1 Description ............................................................................................................683 7.4.2.2 Performance Objectives............. ...........................................................................683 7.4.2.3 Applications/Limitations........................................................................................ .683 7.4.2.4 Criteria...................................................................................................................683 7.4.3 BMP T930 Continuous Inflow Biofiltration Swale ............................................................ 685 7.4.3.1 Description: ........................................................................................................... 685 7.4.3.2 Applications ...........................................................................................................685 7.4.3.3 Design Criteria........................................ ...............................................................685 7.4.4 BMP T940 Basic Filter Strip............................................................................................. 686 7.4.4.1 Description ............................................................................................................686 7.4.4.2 Applications/Limitations............................... ..........................................................686 7.4.4.3 Design Criteria for Filter strips:..............................................................................688 7.4.4.4 Sizing Procedure...................................................................................................688 7.4.5 BMP T950 Narrow Area Filter Strip ................................ ................................................. 689 7.4.5.1 Description: ...........................................................................................................689 7.4.5.2 Applications/Limitations:........................................................................................689 7.4.5.3 Design Criteria:.................................................. ....................................................689 Chapter 8 Wetpool Facilities.............................................................................................691 8.1 Purpose ................................................................................................................................691 8.2 Best Management Practices.............................. ....................................................................691 8.2.1 BMP T1010 Wetponds -Basic and Large ....................................................................... 692 8.2.1.1 Description: ...........................................................................................................692 8.2.1.2 Design Criteria:....................................... ...............................................................692 8.2.1.3 Sizing Procedure...................................................................................................695 8.2.1.4 Wetpool Geometry ................................................................................................701 8.2.1.5 Berms, Baffles, and Slopes........................................ ...........................................701 8.2.1.6 Embankments .......................................................................................................702 8.2.1.7 Inlet and Outlet ......................................................................................................702 8.2.1.8 Access and Setbacks................................................. ...........................................703 8.2.1.9 Planting Requirements..........................................................................................703 8.2.1.10 Recommended Design Features ..........................................................................704 Volume V v Table of Contents 8.2.1.11 Construction Criteria:.............................................................................................707 8.2.1.12 Operation and Maintenance: .................................................................................707 8.2.2 BMP T1020 Wetvaults ........................................................................................ ............. 708 8.2.2.1 Description: ...........................................................................................................708 8.2.2.2 Applications and Limitations:............ .....................................................................708 8.2.2.3 Design Criteria:...................................................................................................... 708 8.2.2.4 Wetpool Geometry ................................................................................................710 8.2.2.5 Vault Structure............................................... ........................................................710 8.2.2.6 Inlet and Outlet ......................................................................................................711 8.2.2.7 Access Requirements ...........................................................................................711 8.2.2.8 Access Roads, Right of Way, and Setbacks............................ .............................711 8.2.2.9 Recommended Design Features ..........................................................................712 8.2.2.10 Construction Criteria...................... ........................................................................712 8.2.2.11 Operation and Maintenance..................................................................................712 8.2.2.12 Modifications for Combining with a Baffle Oil/Water Separator ............................713 8.2.3 BMP T1030 Stormwater Treatment Wetlands................................................... .............. 714 8.2.3.1 Description ............................................................................................................714 8.2.3.2 Applications and Limitations............ ......................................................................714 8.2.3.3 Design Criteria...................................................................................................... .714 8.2.3.4 Sizing Procedure...................................................................................................714 8.2.3.5 Wetland Geometry .......................................... ......................................................715 8.2.3.6 Lining Requirements .............................................................................................715 8.2.3.7 Inlet and Outlet ......................................................................................................716 8.2.3.8 Access and Setbacks......................................... ...................................................716 8.2.3.9 Planting Requirements..........................................................................................719 8.2.3.10 Construction Criteria..............................................................................................719 8.2.3.11 Operation and Maintenance.............................................. ....................................719 8.2.4 BMP T1040 Combined Detention and Wetpool Facilities ............................................... 720 8.2.4.1 Description: ............................ ...............................................................................720 8.2.4.2 Applications and Limitations:............................................................................... ..720 8.2.4.3 Design Criteria:......................................................................................................720 8.2.4.4 Sizing................................................. ....................................................................723 8.2.4.5 Detention and Wetpool Geometry.........................................................................723 8.2.4.6 Berms, Baffles and Slopes....................................................................................723 8.2.4.7 Inlet and Outlet ..................................................... .................................................723 8.2.4.8 Access and Setbacks............................................................................................723 8.2.4.9 Planting Requirements..........................................................................................723 8.3 Combined Detention and Wetvault................................................. .......................................724 8.4 Combined Detention and Stormwater Wetland.....................................................................726 8.4.1 Sizing Criteria .................................................................................................................. 726 8.4.2 Design Criteria .......................................................... ....................................................... 726 8.4.3 Inlet and Outlet Criteria.................................................................................................... 726 8.4.4 Planting Requirements .................................................................................................... 726 Volume V vi Table of Contents Chapter 9 Oil and Water Separators.................................................................................727 9.1 Purpose ...................................... ..........................................................................................727 9.2 Description.......................................................................................... ..................................727 9.3 Applications/Limitations .........................................................................................................727 9.4 Site Suitability ........................................................................................................................730 9.5 Design Criteria............................................ ...........................................................................731 9.5.1 General Considerations ........................................................................................... ........ 731 9.5.2 Criteria for Separator Separator Bays .............................................................................................. 731 9.5.3 Criteria for Baffles ............................................................................................................ 732 9.6 Oil and Water Separator BMPs ..................................................... ........................................732 9.6.1 BMP T1110 API (Baffle type) Separator Bay .................................................................. 733 9.6.1.1 Design Criteria............. ..........................................................................................733 9.6.1.2 Sizing Criteria ................................................................................. .......................733 9.6.2 BMP T1111 Coalescing Plate (CP) Separator Bay ......................................................... 735 9.6.2.1 Design Criteria................................... ....................................................................735 9.6.2.2 Operation and Maintenance..................................................................................735 Chapter 10 Emerging Technologies...................................................................................737 10.1 Background................................................................. ..........................................................737 10.2 Emerging Technology and the City of Auburn.......................................................................737 10.3 Ecology Role in Evaluating Emerging Technologies.............................................................737 10.4 Evaluation of Emerging Technologies......................................... ..........................................737 10.5 Assessing Levels of Development of Emerging Technologies .............................................738 10.6 Examples of Emerging Technologies for Stormwater Treatment and Control ......................739 Appendix A Basic Treatment Receiving Waters .................................................................741 Appendix B Procedure for Conducting a Pilot Infiltration Test .........................................743 Appendix C Geotextile Specifications ....................................................... ..........................745 Appendix D Turbulence and Short-Circuiting Factor .........................................................747 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Purpose Volume V Content and Organization 6 03 Introduction Volume V: Water Quality Treatment BMPs Purpose of this Volume This volume focuses on treatment of runoff to remove pollutants at developed sites. Typical pollutants of concern include sand, silt, and other suspended solids; metals such as copper, lead, and zinc; nutrients (e.g., nitrogen and phosphorous); certain bacteria and viruses; and organics such as petroleum hydrocarbons and pesticides. Methods of pollutant removal include sedimentation/settling, filtration, infiltration, plant uptake, ion exchange, adsorption, and bacterial decomposition. Floatable pollutants such as oil, debris, and scum can be removed with separator structures. The purpose of this volume is to provide criteria for selection and design of permanent runoff treatment facilities. Use this volume to select permanent water quality treatment BMPs. Include the BMPs and the design criteria used in your your Stormwater Site Plan (see Volume I). This volume should be used as an aid in designing and constructing water quality treatment BMPs. Content and Organization of this Volume Volume V contains ten chapters and four appendices: • Chapter 1 outlines a step-by-step process for selecting treatment facilities for new development and redevelopment projects. • Chapter 2 presents treatment facility “menus” that are used in applying the step-bystep process presented in Chapter 1. These menus cover different treatment needs that are associated with different sites. • Chapter 3 discusses general requirements for treatment facilities. • Chapter 4 describes using a pretreatment facility to remove suspended solids prior to runoff treatment facilities. • Chapter 5 through Chapter 9 provide detailed information regarding specific types of treatment facilities identified in the menus in Chapter 2. • Chapter 10 discusses special considerations for emerging technologies for stormwater treatment. • The appendices provide more detailed information on selected topics referenced in the preceding chapters. Volume V S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 04 Chapter 1 Chapter 1 Treatment Facility Selection Process This chapter describes a step-by-step process for selecting the type of treatment facilities that will apply to individual projects. 1.1 Step-by-Step Selection Process for Treatment Facilities Use the step-by-step process outlined below to determine the type of treatment facilities applicable to the project. Step 1. Determine the receiving waters and pollutants of concern Step 2. Determine if oil treatment is required Step 3. Determine if infiltration for pollutant removal is possible Step 4. Determine if control of phosphorus is required Step 5. Determine if enhanced treatment is required Step 6. Determine if basic treatment is required Step 7. Consider other factors that may influence the selection of a treatment facility Step 8. Select an appropriate treatment facility or treatment train for each type of treatment required Step 1: Determine the Receiving Waters and Pollutants of Concern Based on Offsite Analysis The project proponent must determine the natural receiving water for the stormwater drainage from the project site (groundwater, wetland, lake, stream, or salt water). This is necessary to determine the applicable treatment menu from which to select treatment facilities. If the discharge is to the City of Auburn’s municipal storm drainage system, the applicant must determine the final discharge point. Watershed specific requirements and/or specific protection areas are outlined in Chapter 2 of Volume V. Step 2: Determine if an Oil Control Facility/Device is Required Oil control is required for projects that have high-use sites. High-use sites are those that typically generate high concentrations of oil due to high traffic turnover or the frequent transfer of oil. High-use sites include: • An area of a commercial or industrial site subject to an expected average daily traffic (ADT) count equal to or greater than 100 100 vehicles per 1,000 square feet of gross building area; • An area of a commercial or industrial site subject to petroleum storage and transfer in excess of 1,500 gallons per year, not including routinely delivered heating oil; • An area of a commercial or industrial site subject to parking, storage or maintenance of 25 or more motorized vehicles that are over 10 tons gross weight (trucks, buses, trains, heavy equipment, etc.); S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 05 Chapter 1 • A road intersection with a measured ADT count of 25,000 vehicles or more on the main roadway and 15,000 vehicles or more on any intersecting roadway, excluding projects proposing primarily pedestrian or bicycle use improvements. The traffic count can be estimated using information from “Trip Generation” published by the Institute of Transportation Engineers, or from a traffic study prepared by a professional engineer or transportation specialist with experience in traffic estimation. The following urban land uses are likely to have areas that fall within the definition of “high-use sites” or have sufficient quantities of free oil present that can be treated by an API or CP-type oil/water separator: • Industrial Machinery and Equipment, and Railroad Equipment Maintenance • Log Storage and Sorting Yards • Aircraft Maintenance Areas • Railroad Yards • Fueling Stations • • Vehicle Maintenance and Repair • Construction Businesses (paving, heavy equipment storage and maintenance, storage of petroleum products) • Any other sites that generate high concentrations of oil. In general, all-day parking areas are not intended to be defined as high-use sites, and should not require oil control treatment outlined in Section 2.1. Gasoline stations, with or without small food stores, will likely exceed the high-use site threshold. The petroleum storage and transfer criterion is intended to address regular transfer operations such as gasoline service stations, not occasional filling of heating oil tanks. Note: Some land use types require the use of a spill control (SC-type) oil/water separator. Those situations are described in IV and are separate from this oil treatment requirement. Step 3: Determine if Infiltration for Pollutant Removal is Possible Use Volume V, Chapter 5 as a guide to determine if the site contains soils that are conducive to infiltration. For sites located in Groundwater Protection Area 2 (see Volume I, Chapter 2) this option is not allowed. Infiltration treatment facilities must be preceded by a pretreatment facility, such as a presettling basin or vault, to reduce the occurrence of plugging. Any of the basic treatment facilities, and detention ponds designed to meet flow control requirements, can also be used for pretreatment. If an oil/water separator is necessary for oil control, it can also function as the pre-settling basin as long as the influent suspended solids concentrations are not high. However, frequent inspections are necessary to determine when accumulated solids exceed the 6-inch depth at which clean-out is recommended. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 06 Chapter 1 Step 4: Determine if Phosphorus Treatment is Required Step 5: Determine if Enhanced Treatment is Required Enhanced treatment is required for the following project sites that discharge to fish-bearing streams, lakes, or to waters or conveyance systems tributary to fish-bearing streams or lakes: • Industrial sites, • Commercial sites, • Multi-family sites, and • High AADT roads as follows: o Fully controlled and partially controlled limited access highways with Annual Average Daily Traffic (AADT) counts of 15,000 or more o All other roads with an AADT of 7,500 or greater Sites listed above that discharge directly (or, indirectly through a municipal storm sewer system) to Basic Treatment Receiving Waters, and portions of the above-listed project sites that are only subject to Basic Treatment requirements (see Step 6) are not required to provide enhanced treatment. For developments with a mix of land use types, the Enhanced Treatment requirement shall apply when the runoff from the areas subject to the Enhanced Treatment requirement comprises 50% or more of the total runoff within a threshold discharge area. Basic Treatment Receiving Waters within the City of Auburn include the Green River and the White River. Basic Treatment Receiving Waters identified by Ecology are listed in Appendix A. If the project must apply Enhanced Treatment, select and apply an appropriate Enhanced Treatment facility. Please refer to the Enhanced Treatment Menu in Section 2.3. Select an option from the menu after reviewing the applicability and limitations, site suitability, and design criteria of each for compatibility with the site. You may also use Table V-1-1 for an initial screening of options. Step 6: Select a Basic Treatment Facility Basic treatment is required for all sites that meet the treatment thresholds of minimum requirement #6, see Volume I, Chapter 3. Typical sites that require basic basic treatment include: • Project sites that discharge to the ground, UNLESS: o The soil suitability criteria for infiltration treatment are met (see Volume III, Chapter 3), or o The project uses infiltration strictly for flow control – not treatment -and the discharge is within ¼ mile of a phosphorus sensitive lake (use the Phosphorus Treatment Menu) or within ¼ mile of a fish-bearing stream or lake (use the Enhanced Treatment Menu). • Residential projects not otherwise needing phosphorus control as determined in Step 4. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 07 Chapter 1 • Project sites discharging directly to salt waters, river segments and lakes listed in Volume V, Appendix A. • Project sites that drain to streams that are not fish-bearing, or to waters not tributary to fish-bearing streams. • Landscaped areas of industrial, commercial, and multi-family project sites, and parking lots of industrial and commercial project sites, dedicated solely to parking of employees’ private vehicles that do not involve any other pollution-generating sources (e.g., industrial activities, customer parking, and storage of erodible or leachable material, wastes, or chemicals). For developments with a mix of land use types, the Basic Treatment requirement shall apply when the runoff from the areas subject to the Basic Treatment requirement comprises 50% or more of the total runoff within a threshold discharge area. Please refer to the Basic Treatment Menu in Section 2.4. Select an option from the menu after reviewing the applicability and limitations, site suitability, and design criteria of each for compatibility with the site. Step 7: Consider Other Factors that May Influence the Selection of a Treatment Device Base the selection of a treatment facility on site physical factors and pollutants of concern. Try to choose a facility that is more likely to do a better job removing the types of pollutants generated on the site regardless of treatment requirements. The types of site physical factors that influence facility selection are summarized below. 1. Pollutants of Concern Consider the land uses and potential pollutants associated with that land use. 2. Soil Type (Table V-1-1) The permeability of the soil underlying an infiltration treatment facility can influence effectiveness. This is particularly true for infiltration treatment facilities that are best sited in sandy to loamy sand soils. They are not generally appropriate for sites that have final infiltration rates (f) of less than 0.5 inches per hour. Wet pond facilities situated on coarser soils will need a synthetic liner or the soils will need to be amended to reduce the infiltration rate and provide treatment. Maintaining a permanent pool in the first cell is necessary to avoid resuspension of settled solids. Biofiltration swales in coarse soils can also be amended to reduce the infiltration rate. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 08 Chapter 1 3. High Sediment Input High total suspended solids (TSS) loads can clog infiltration soil, sand filters, and coalescing plate oil/water separators. Pretreatment with a presettling basin, wet vault, or another basic treatment facility would typically be necessary. Other Physical Factors • Slope: Steep slopes restrict the use of several BMPs. For example, biofiltration swales are usually situated on sites with slopes of less than 6%, although greater slopes can be considered. Infiltration BMPs are not suitable when the slope exceeds 20%. • High Water Table: Unless there is sufficient horizontal hydraulic receptor capacity the water table acts as an effective barrier to exfiltration and can sharply reduce the efficiency of an infiltration system. If the high water table extends to within five (5) feet of the bottom of an infiltration BMP, the site is seldom suitable. • Depth to Bedrock/Hardpan/Till: The downward exfiltration of stormwater is also impeded if a bedrock or till layer lies too close to the surface. If the impervious layer lies within five feet below the bottom of the infiltration BMP the site is not suitable. Similarly, pond BMPs are often not feasible if bedrock lies within the area that must be excavated. • Proximity to Foundations and Wells: Since infiltration BMPs convey runoff back into the soil, some sites may experience problems with local seepage. This can be a real problem if the BMP is located too close to a building foundation. Another risk is groundwater pollution; hence the requirement to site infiltration systems more than 100 feet away from drinking water wells. • Maximum Depth: Wet ponds are also subject to a maximum depth limit for the "permanent pool" volume. Deep ponds (greater than 8 feet) may stratify during summer and create low oxygen conditions near the bottom resulting in re-release of phosphorus and other pollutants back into the water. water. Step 8: Select an Appropriate Treatment Device Refer to the treatment facility menus in Chapter 2 for treatment facility options. Use Table V-1-1 as an aid in determining which treatment device is most appropriate for the site. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Volume V Selection Process 6 09 Chapter 1 Table V-1-1. Screening Treatment Facilities Based on Soil Type Soil Type Infiltration Wet Pond* Biofiltration* (Swale or Filter Strip) Coarse Sand or Cobbles N N N Sand Y N N Loamy Sand Y N Y Sandy Loam Y N Y Loam N N Y Silt Loam N N Y Sandy Clay Loam N Y Y Silty Clay Loam N Y Y Sandy Clay N Y Y Silty Clay N Y N Clay N Y N Y Indicates that use of the technology is generally appropriate for this soil type. N Indicates that use of the technology is generally not appropriate for this soil type * Coarser soils may be used for these facilities if a liner is installed to prevent infiltration, or if the soils are amended to reduce the infiltration rate. Sand filtration is not listed because its feasibility is not dependent on soil type. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Menus Volume V 6 10 Chapter 2 Chapter 2 Treatment Facility Menus This chapter identifies the treatment facility menus. The menus in this chapter are as follows: • Oil Control Menu, Section 2.1 • Phosphorus Treatment Menu, Section 2.2 • Enhanced Treatment Menu, Section 2.3 • Basic Treatment Menu, Section 2.4 Performance goals apply to the water quality design storm volume or flowrate, whichever is applicable, and apply on an average annual basis to the entire annual discharge volume (treated plus bypassed). The incremental portion of runoff in excess of water quality design flowrate can be routed around the facility (off-line treatment facilities) or can be passed through the facility untreated (on-line treatment facilities) provided a net pollutant reduction is maintained. All performance goals apply to stormwater typically found in Pacific Northwest maritime climates, where long duration, low intensity storms storms predominate and stormwater contains mostly silt-sized particles. 2.1 Oil Control Menu This menu is applicable in addition to facilities required by other treatment menus. 2.1.1 Performance Goal The oil control menu facility options should achieve the goals of no ongoing or recurring visible sheen, and to have a 24-hour average Total Petroleum Hydrocarbon (TPH) concentration no greater than 10 mg/l, and a maximum of 15 mg/l for a discrete sample (grab sample). 2.1.2 Options Oil control options include facilities that are small, treat runoff from a limited area, and require frequent maintenance as well as facilities that treat runoff from larger areas and generally require less frequent maintenance. • API-Type Oil/Water Separator – See Chapter 9 • Coalescing Plate Oil/Water Separator – See Chapter 9 • Linear Sand Filter – See Chapter 6 The linear sand filter is used in the Basic, Enhanced, and Phosphorus Treatment menus also. If used to satisfy one of those treatment requirements, the same facility shall not also be used to satisfy the oil control requirement unless enhanced maintenance is assured. This is to prevent clogging of the filter by oil so that it will function for suspended solids and other pollutant removal as well. Quarterly cleaning is required when used as a combination facility. • Emerging Stormwater Treatment Technologies for Oil Treatment – See Chapter 10 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Menus Volume V 6 11 Chapter 2 2.1.3 Application on the Project Site Place oil control facilities upstream of other facilities, as close to the source of oil generation as practical. For high-use sites located within a larger commercial center, only the impervious surface associated with the high-use portion of the site is subject to oil treatment requirements. If common parking for multiple businesses is provided, treatment shall be applied to the number of parking stalls required for the high-use business only. If the treatment collection area also receives runoff from other areas, the treatment facility must be sized to treat all water passing through it. High-use roadway intersections shall treat lanes where vehicles accumulate during the traffic signal cycle, including left and right turn lanes and through lanes, from the beginning of the left turn pocket. If no left turn pocket exists, the treatable area shall begin at a distance equal to three car lengths from the stop line. If runoff from the intersection drains to more than two collection areas that do not combine within the intersection, treatment may be limited to any two of the collection areas. 2.2 Phosphorus Treatment Menu 2.2.1 Performance Goal The phosphorus menu facility choices should achieve a goal of 50% total phosphorus removal for a range of influent concentrations between 0.1 – 0.5 mg/l. The phosphorus menu facility choices must achieve basic treatment goals in addition to phosphorus. 2.2.2 Options Any one of the following options may be chosen to satisfy the phosphorus treatment requirement. • Infiltration with appropriate pretreatment – See Chapter 4 and Chapter 5 o Infiltration Treatment -If infiltration is through soils meeting the minimum site suitability criteria for infiltration treatment (see Chapter 5), a presettling basin or a basic treatment facility can serve for pretreatment. o Infiltration Proceeded by Basic Treatment -If infiltration is through soils that do not meet the soil suitability criteria for infiltration treatment, treatment must be provided by a basic treatment facility unless the soil and site fit the description in the next option below. o Infiltration Preceded by Phosphorus Treatment -If the soils do not meet the soil suitability criteria and the infiltration site is within ¼ mile of a phosphorus-sensitive receiving water, or a tributary to that water, treatment must be provided by one of the other treatment facility options listed below. • Large Sand Filter – See Chapter 6 • Large Wetpond – See Chapter 8 • Emerging Stormwater Treatment Technologies for Phosphorus Treatment – See Chapter 10 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Menus Volume V 6 12 Chapter 2 • Two-Facility Treatment Trains – See Table V-2-2. Table V-2-2. Treatment Trains for Phosphorus Removal First Basic Treatment Facility Second Treatment Facility Biofiltration Swale Basic Sand Filter or Sand Filter Vault Filter Strip Linear Sand Filter (no presettling needed) Linear Sand Filter Filter Strip Basic Wetpond Basic Sand Filter or Sand Filter Vault Wetvault Basic Sand Filter or Sand Filter Vault Stormwater Treatment Wetland Basic Sand Filter or Sand Filter Vault Basic Combined Detention and Wetpool Basic Sand Filter or Sand Filter Vault 2.3 Enhanced Treatment Menu 2.3.1 Performance Goal The enhanced treatment facility choices should provide a higher rate of removal of dissolved metals than basic treatment facilities. The performance goal assumes that the facility is treating stormwater with influent dissolved copper ranging from 0.003 to 0.02 mg/l, and dissolved zinc ranging from 0.02 to 0.3 mg/l. Enhanced treatment facilities must achieve basic treatment goals in addition to enhanced treatment goals. 2.3.2 Options Any one of the following options may be chosen to satisfy the enhanced treatment requirement: • Infiltration with appropriate pretreatment – See Chapter 4 and Chapter 5 o Infiltration Treatment -If infiltration is through soils meeting the minimum site suitability criteria for infiltration treatment (see Chapter 5), a presettling basin or a basic treatment facility can serve for pretreatment. o Infiltration Proceeded by Basic Treatment -If infiltration is through soils that do not meet the soil suitability criteria for infiltration treatment, treatment must be provided by a basic treatment facility unless the soil and site fit the description in the next option below. o Infiltration Preceded by Enhanced Treatment -If the soils do not meet the soil suitability criteria and the infiltration site is within ¼ mile of a fish-bearing stream or a tributary to a fish-bearing stream treatment must be provided by one of the other treatment facility options listed below. • Large Sand Filter – See Chapter 6 • Stormwater Treatment Wetland – See Chapter 8 • Two Facility Treatment Trains – See Table V-2-3 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Menus Volume V 6 13 Chapter 2 • Compost-Amended Filter – See Chapter 7 • Bioretention/rain garden – See Volume VI NOTE: Where bioretention/rain gardens are intended to fully meet treatment requirements, they must be designed, using an approved continuous runoff model, to infiltrate 91% of the influent runoff volume. • Emerging Stormwater Treatment Technologies for Enhanced Treatment – See Chapter 10 Table V-2-3. Treatment Trains for Enhanced Treatment First Basic Treatment Facility Second Treatment Facility Biofiltration Swale Basic Sand Filter or Sand Filter Vault or Media Filter1 Filter Strip Linear Sand Filter with no pre-settling cell needed Linear Sand Filter Filter Strip Basic Wetpond Basic Sand Filter or Sand Filter Vault or Media Filter1 Wetvault Basic Sand Filter or Sand Filter Vault or Media Filter1 Basic Combined Detention/Wetpool Basic Sand Filter or Sand Filter Vault or Media Filter1 Basic Sand Filter or Sand Filter Vault with a presettling cell if the filter isn’t preceded by a detention facility Media Filter1 1 The media must be of a type approved for use by Ecology. Refer to Ecology’s website. 2.4 Basic Treatment Menu 2.4.1 Performance Goal The basic treatment menu facility options should achieve 80% removal of total suspended solids (TSS) for influent concentrations ranging from 100 to 200 mg/L. For influent concentrations greater than 200 mg/l, a higher treatment goal is appropriate. For influent concentrations less than 100 mg/l, the facilities should achieve an effluent goal of 20 mg/l total suspended solids. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Treatment Facility Menus Volume V 6 14 Chapter 2 2.4.2 Options Any one of the following options may be chosen to satisfy the basic treatment requirement: • Bio-infiltration Swale – See Chapter 5 • Infiltration – See Chapter 5 • Sand Filters – See Chapter 6 • Biofiltration Swales – See Chapter 7 • Filter Strips – See Chapter 7 • Basic Wetpond – See Chapter 8 • Wetvault – See Chapter 8 A wetvault may be used for commercial, industrial, or road projects if there are space limitations. The use of wetvaults is discouraged for residential projects. Combined detention/wetvaults are allowed (see Section 8.3). • Stormwater Treatment Wetland – See Chapter 8 • Combined Detention and Wetpool Facilities – See Chapter 8 • Bioretention/Rain Garden – See Volume VI • Emerging Stormwater Treatment Technologies for Basic Treatment – See Chapter 10 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 15 Chapter 3 Chapter 3 General Requirements for Stormwater Facilities This chapter addresses general requirements for treatment facilities. Requirements discussed in this chapter include design volumes and flows, sequencing of facilities, liners, and hydraulic structures for splitting or dispersing flows. • All open detention and retention ponds shall be appropriately and aesthetically located, designed, and planted. Pre-approval of the design concept, including landscaping, is required for all proposed public ponds. Joint use facilities incorporating recreation or open space opportunities are encouraged. • All storm facility landscape planting and seeding plans shall be prepared and sealed by a Washington State licensed professional Landscape Architect or similar specialist approved by the City of Auburn. • Water quality systems shall be designed for simplicity and ease of maintenance. • Treatment systems shall be designed such that storm drainage from public streets does not discharge into areas of private ownership or private maintenance responsibility unless a holdharmless and cross drainage agreement has been secured. • The City prefers retention (infiltration) for storm drainage quantity control when soil conditions are satisfactory for such application and water quality treatment can be provided. 3.1 Design Flow Volume and Flow Rate 3.1.1 Water Quality Design Flow Volume The volume of runoff predicted from a 24-hour storm with a 6-month return frequency (a.k.a., 6-month, 24-hour storm) obtained from an approved single event model. The 6-month, 24-hour design storm of 1.44 inches shall be used in the City of Auburn. Alternatively, the 91st percentile, 24-hour runoff volume indicated by the Western Washington Hydrology Model (WWHM) will be used to determine the water quality design flow volume. Treatment facility sizes are the same whether they precede, follow or are incorporated (i.e., combined detention and wetpool facilities) into the detention facility. Treatment options that can be sized by this method include: • Wetponds • Wetvaults • Stormwater Wetlands • Combined Detention and Wetpool Facilities S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 16 Chapter 3 3.1.1 Water Quality Design Flow Rate A. Preceding Detention Facilities or when Detention Facilities are not required: The flow rate at or below which 91% of the runoff volume, as estimated by WWHM, will be treated • All BMPs except wetpool type facilities (Chapter 8) shall use the 15-minute time series from WWHM. Design criteria for treatment facilities are assigned to achieve the applicable performance goal (e.g., 80 percent TSS removal) at the water quality design flow rate. • Off-line facilities: For treatment facilities not preceded by an equalization or storage basin, and when runoff flow rates exceed the water quality design flow rate, the treatment facility shall continue to receive and treat the water quality design flow rate to the applicable treatment performance goal. The incremental portion of runoff in excess of the water quality design flowrate can be routed around the facility. Treatment facilities preceded by an equalization or storage basin may identify a lower water quality design flow rate provided that at least 91 percent of the estimated runoff volume in the time series of an approved continuous runoff model is treated to the applicable performance goals (e.g., 80 percent TSS removal at the water quality design flow rate and 80 percent TSS removal on an annual average basis). • On-line facilities: Runoff flow rates in excess of the water quality design flow rate can be routed through the facility provided a net pollutant reduction is maintained, and the applicable annual average performance goal is met. B. Downstream of Detention Facilities: The full 2-year release rate from the detention facility • An approved continuous runoff model shall identify the 2-year return frequency flow rate discharged by a detention facility that is designed to meet the flow duration standard. • Treatment facilities downstream of detention can be designed on-line or off-line. For off-line facilities, the entire water quality design flow volume/rate must be treated. Only flows in excess of the design flow may be bypassed. 3.1.2 Flows Requiring Treatment Runoff from pollution-generating impervious or pervious surfaces exceeding the thresholds outlined in Minimum Requirement #6 (Volume I, Chapter 3) must be treated using the water quality facilities in this volume. If runoff from non-pollution generating surfaces reaches a runoff treatment BMP, flows from those areas must be included in the sizing calculations for the facility. Once runoff from nonpollution generating areas is mixed with runoff from pollution-generating areas, it cannot be separated before treatment. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 17 Chapter 3 The following are some examples of surfaces that are required to provide treatment if threshold limits for treatment are met: • Runoff from pollution-generating impervious surfaces (e.g. roads (paved or unpaved), driveways, parking lots, storage yards, bike lanes within the roadway, unvegetated road shoulders, etc.) • Runoff from any pervious or non-impervious surface subject to the use of pesticides and fertilizers or soil loss. • Runoff from pervious parking areas. • Runoff from metal roofs unless they are coated with an inert non-leachable material. 3.2 Sequence of Facilities Treatment facilities can be placed in a variety of configurations. Some are required to be upstream from detention facilities while others may perform better if located downstream. Detention facilities can act as settling basins and therefore can reduce the load going to a treatment facility. Additionally, treatment facilities can be sequenced together to provide a higher level of treatment that could be achieved by a single facility. For instance, the enhanced treatment and phosphorus removal menus, described in Chapter 2, include treatment options in which more than one type of treatment facility is used, for these treatment trains the sequencing is prescribed. Table V-3-4 summarizes placement considerations of treatment facilities in relation to detention facilities. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 18 Chapter 3 Table V-3-4. Treatment Facility Placement in Relation to Detention Facilities Water Quality Facility Preceding Detention Following Detention Basic biofiltration swale (Chapter 7) OK OK. Prolonged flows may reduce grass survival. Consider wet biofiltration swale Wet biofiltration swale (Chapter 7) OK OK Filter strip (Chapter 7) OK No—must be installed before flows concentrate. Basic or large wetpond (Chapter 8) OK OK—less water level fluctuation in ponds downstream of detention may improve aesthetic qualities and performance. Wetvault (Chapter 8) OK OK Basic or large sand filter or sand filter vault (Chapter 6) OK, but presettling and control of floatables needed OK—sand filters downstream of detention facilities may require field adjustments if prolonged flows cause sand saturation and interfere with phosphorus removal. Stormwater treatment wetland/pond (Chapter 8) OK OK—less water level fluctuation and better plant diversity are possible if the stormwater wetland is located downstream of the detention facility. 3.3 Setbacks, Slopes, and Embankments The following guidelines for setbacks, slopes, and embankments are intended to provide for adequate maintenance accessibility to runoff treatment facilities. Setback requirements may also be specified by Auburn City Code, Uniform Building Code requirements, or other state regulations. 3.3.1 Setbacks The City requires specific setbacks for sites with steep slopes, landslide areas, open water features, springs, wells, and septic tank drain fields. Setbacks from tract lines are necessary for maintenance access and equipment maneuverability. Adequate room for maintenance equipment shall also be considered during site design. Project proponents should consult the Auburn City Codes to determine all applicable setback requirements. Where a conflict between setbacks occurs, the City shall require compliance with the most stringent of the setback requirements from the various codes/regulations. Required setbacks are as follows or as determined by a qualified geotechnical engineer: • Minimum spacing between trenches shall be 4 feet measured from the edge of trench. • Stormwater infiltration facilities, unlined wetponds and detention ponds shall be set back at least 100 feet from open water features, drinking water wells, septic tanks or drainfields, and S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 19 Chapter 3 springs used for public drinking water supplies. Infiltration facilities, unlined wetponds and detention ponds upgradient of drinking water supplies and within 1, 5, and 10-year time of travel zones must comply with Health Department requirements (Washington Wellhead Protection Program, DOH, 12/93). • All systems shall be at least 10 feet from any structure. If necessary, setbacks shall be increased from the minimum 10 feet in order to maintain a 1:1 side slope for future excavation and maintenance • All systems shall be placed at least 5 feet from any property line. If necessary, setbacks shall be increased from the minimum 5 feet in order to maintain a 1:1 side slope for future excavation and maintenance. • All facilities shall be setback from sensitive areas, steep slopes, landslide hazard areas, and erosion hazard areas as governed by the Auburn City Code. Runoff discharged near landslide hazard areas must be evaluated by a geotechnical engineer or qualified geologist. The discharge point shall not be placed on or above slopes greater than 20% or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and City approval. • For sites with septic systems, infiltration systems, unlined wetponds and detention ponds shall be downgradient of the drainfield unless the site topography clearly prohibits subsurface flows from intersecting the drainfield. • Infiltration system shall be set back from sensitive areas, steep slopes, landslide hazard areas, and erosion hazard areas as governed by the Auburn City Code. Runoff discharged near landslide hazard areas must be evaluated by a geotechnical by a geotechnical engineer or qualified geologist. The discharge point shall not be placed on or above slopes greater than 20% (5H:1V) or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and City approval. Additional setbacks for specific stormwater facilities will be noted in the appropriate section. 3.3.2 Side Slopes and Embankments • Side slopes shall not exceed a slope of 3H:1V. Moderately undulating slopes are acceptable and can provide a more natural setting for the facility. In general, gentle side slopes improve the aesthetic attributes of the facility and enhance safety. • Interior side slopes may be retaining walls if the design is prepared and stamped by a licensed civil engineer. A fence shall be provided along the top of the wall. • Maintenance access shall be provided through an access ramp or other adequate means (see Volume III, Chapter 2, Section 2.3.1). • Embankments that impound water must comply with the Washington State Dam Safety Regulations (Chapter 173-175 WAC). See Volume III, Chapter 3 for more detail concerning Detention Ponds. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 20 Chapter 3 3.4 Facility Liners Liners are intended to reduce the likelihood that pollutants in stormwater will reach groundwater. Where necessary, a liner is incorporated into the base of the treatment facility as the facility is constructed. In addition to groundwater protection considerations, some facility types require permanent water for proper functioning. An example is the first cell of a wetpond. 3.4.1 General Design Criteria • Table V-3-5 shows recommendations for the type of liner generally best suited for use with various runoff treatment facilities. • Liners shall be evenly placed over the bottom and/or sides of the treatment area of the facility as indicated in Table V-3-5. Areas above the treatment volume that are required to pass flows greater than the water quality treatment flow (or volume) need not be lined. However, the lining must be extended to the top of the interior side slope and anchored if it cannot be permanently secured by other means. • For low permeability liners, the following criteria apply: o Where the seasonal high groundwater elevation is likely to contact a low permeability liner, liner buoyancy may be a concern. A low permeability liner shall not be used in this situation unless evaluated and recommended by a geotechnical engineer. o Where grass must be planted over a low permeability liner per the facility design, a minimum of 6 inches of good topsoil or compost-amended native soil (2 inches compost tilled into 6 inches of native till soil) must be placed over the liner in the area to be planted. Twelve inches of cover is preferred. • Check all liners for buoyancy stability and include calculations in project documentation. Provide anchors as needed. • If a treatment liner will be below the seasonal high water level, the pollutant removal performance of the liner must be evaluated by a geotechnical or groundwater specialist and found to be as protective as if the liner were above the level of the groundwater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 21 Chapter 3 Table V-3-5. Lining Types Recommended for Runoff Treatment Facilities WQ Facility Area to be Lined Type of Liner Recommended Presettling basin Bottom and sides Low permeability liner or Treatment liner (If the basin will intercept the seasonal high groundwater table, a treatment liner is recommended.) Wetpond First cell: bottom and sides to WQ design water surface ----------------------------------Second cell: bottom and sides to WQ design water surface Low permeability liner or Treatment liner (If the wet pond will intercept the seasonal high groundwater table, a treatment liner is recommended.) --------------------------------Treatment liner Combined detention/WQ facility First cell: bottom and sides to WQ design water surface ----------------------------------Second cell: bottom and sides to WQ design water surface Low permeability liner or treatment liner liner (If the facility will intercept the seasonal high groundwater table a treatment liner is recommended.) --------------------------------Treatment liner Stormwater wetland Bottom and sides, both cells Low permeability liner (If the facility will intercept the seasonal high groundwater table, a treatment liner is recommended.) Sand filtration basin Basin sides only Treatment liner Sand filter vault Not applicable No liner needed Linear sand filter Not applicable if in vault Bottom and sides of presettling cell if not in vault No liner needed Low permeability or treatment liner Media filter (in vault) Not applicable No liner needed Wet vault Not applicable No liner needed S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 22 Chapter 3 3.4.2 Design Criteria for Treatment Liners • A two-foot thick layer of soil with a minimum organic content of 5% and a minimum cation exchange capacity (CEC) of 5 milliequivalents/100 grams can be used as a treatment layer beneath a water quality or detention facility. • To demonstrate that in-place soils meet the above criteria, one sample per 1,000 square feet of facility area shall be tested. Each sample shall be a composite of subsamples taken throughout the depth of the treatment layer (usually two to six feet below the expected facility invert). • Typically, side wall seepage is not a concern if the seepage flows through the same stratum as the bottom of the treatment BMP. However, if the treatment soil is an engineered soil or has very low permeability, the potential to bypass the treatment soil through the side walls may be significant. In those cases, the treatment BMP side walls may be lined with at least 18 inches of treatment soil, as described above, to prevent untreated seepage. This lesser soil thickness is based on unsaturated flow as a result of alternating wet-dry periods. • Organic content shall be measured on a dry weight basis using ASTM D2974. • Cation exchange capacity (CEC) shall be tested using EPA laboratory method 9081. • Certification by a soils testing laboratory that imported soil meets the organic content and CEC criteria above shall be provided to the City of Auburn. • Animal manures used in treatment soil layers must be sterilized because of potential for bacterial contamination of the groundwater. 3.4.3 Design Criteria for Low Permeability Liner Options This section presents the design criteria for each of the following four low permeability liner options: compacted till liners, clay liners, geomembrane liners, and concrete liners. 3.4.3.1 Compacted Till Liners • Liner thickness shall be 18 inches after compaction. • Soil shall be compacted to 95% minimum dry density, modified proctor method (ASTM D-1557). • A different depth and density sufficient to retard the infiltration rate to 2.4 x 10-5 inches per minute (1 x 10-6 cm/s) may also be used instead of the above criteria. • Soil shall be placed in 6-inch lifts. • Reference Table V-3-6 for Acceptable Gradation for Compacted Till Liners. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 23 Chapter 3 Table V-3-6. Acceptable Gradation for Compacted Till Liners Sieve Size Percent Passing 6-inch 100 4-inch 90 #4 70 -100 #200 20 3.4.3.2 Clay Liners • Liner thickness shall be 12 inches. • Clay shall be compacted to 95% minimum dry density, modified proctor method (ASTM D-1557). • A different depth and density sufficient to retard the infiltration rate to 2.4 x 10-5 inches per minute (1 x 10-6 cm/s) may also be used instead of the above criteria. • The slope of clay liners must be restricted to 3H: IV for all areas requiring soil cover; otherwise, the soil layer must be stabilized by another method so that soil slippage into the facility does not occur. Any alternative soil stabilization method must take maintenance access into consideration. • Where clay liners form the sides of ponds, the interior side slope shall not be steeper than 3H:1V, irrespective of fencing. 3.4.3.3 Geomembrane Liners • Geomembrane liners shall be ultraviolet (UV) light resistant and have a minimum thickness of 30 mils. A thickness of 40 mils shall be used in areas of maintenance access or where heavy machinery must be operated over the membrane. • Geomembranes shall be bedded according to the manufacturer's recommendations. • Liners shall be installed so that they can be covered with 12 inches of top dressing forming the bottom and sides of the water quality facility, except for liner sand filters. Top dressing shall consist of 6 inches of crushed rock covered with 6 inches of native soil. The rock layer is to mark the location of the liner for future maintenance operations. As an alternative to crushed rock, 12 inches of native soil may be used if orange plastic “safety fencing” or another highly-visible, continuous marker is embedded 6 inches above the membrane. • If possible, liners should be of a contrasting color so that maintenance workers are aware of any areas where a liner may have become exposed when maintaining the facility. • Geomembrane liners shall not be used on slopes steeper than 5H:1V to prevent the top dressing material from slipping. Textured liners may be used on slopes up to 3H:1V upon recommendation by a geotechnical engineer that the top dressing will be stable for all site conditions, including maintenance. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 24 Chapter 3 3.4.3.4 Concrete Liners • Portland cement liners are allowed irrespective of facility size, and shotcrete may be used on slopes. However, specifications must be developed by a professional engineer who certifies the liner against cracking or losing water retention ability under expected conditions of operation, including facility maintenance operations. Weight of maintenance equipment can be up to 80,000 pounds when fully loaded. • Asphalt concrete may not be used for liners due to its permeability to many organic pollutants. • If grass is to be grown over a concrete liner, slopes must be no steeper than 5H:1V to prevent the top dressing material from slipping. 3.5 Hydraulic Structures 3.5.1 Flow Splitter Designs 3.5.1.1 General Design Criteria • A flow splitter must be designed to deliver the WQ design flow rate specified in this volume to the WQ treatment facility. • The top of the weir must be located at the water surface for the design flow. Remaining flows enter the bypass line. Flows modeled using a WWHM shall use 15-minute time steps, if available. Otherwise use 1-hour time steps. • The maximum head must be minimized for flow in excess of the WQ design flow. Specifically, flow to the WQ facility at the 100-year water surface must not increase the design WQ flow by more than 10%. • Design as shown in Figure V-3-1 or Figure V-3-2 or provide an equivalent design. • As an alternative to using a solid top plate in Figure V-3-2, a full tee section may be used with the top of the tee at the 100-year water surface. This alternative would route emergency overflows (if the overflow pipe were plugged) through the WQ facility rather than back up from the manhole. • Special applications, such as roads, may require the use of a modified flow splitter. The baffle wall may be fitted with a notch and adjustable weir plate to proportion runoff volumes other than high flows. • For ponding facilities, backwater effects must be considered in determining the height of the standpipe in the manhole. • Ladder or step and handhold access must be provided. If the weir wall is higher than 36 inches, two ladders, one to either side of the wall, must be used. 3.5.1.2 Materials • The splitter baffle may be installed in a Type 2 manhole or vault. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 25 Chapter 3 • The baffle wall must be made of reinforced concrete or another suitable material resistant to corrosion, and have a minimum 4-inch thickness. The minimum clearance between the top of the baffle wall and the bottom of the manhole cover must be 4 feet; otherwise, dual access points shall be provided. • All metal parts must be corrosion resistant. Examples of preferred materials include aluminum, stainless steel, and plastic. Zinc and galvanized materials are prohibited unless coated as approved by the City. Painted metal parts shall not be used because of poor longevity. Figure V-3-1. Flow Splitter, Option A S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 26 Chapter 3 Figure V-3-2. Flow Splitter, Option B S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 27 Chapter 3 3.5.2 Flow Spreading Options Flow spreaders function to uniformly spread flows across the inflow portion of water quality facilities (e.g., sand filter, biofiltration swale, or filter strip). There are five flow spreader options presented in this section: • Option A – Anchored plate (Figure V-3-3) • Option B – Concrete sump box (Figure V-3-4) • Option C – Notched curb spreader (Figure V-3-5) • Option D – Through-curb ports (Figure V-3-6) • Option E – Interrupted curb Options A through C can be used for spreading flows that are concentrated. Any one of these options can be used when spreading is required by the facility design criteria. Options A through C can also be used for unconcentrated flows, and in some cases must be used, such as to correct for moderate grade changes along a filter strip. Options D and E are only for flows that are already unconcentrated and enter a filter strip or continuous inflow biofiltration swale. Other flow spreader options may be allowed with written approval from The City. 3.5.2.1 General Design Criteria • Where flow enters the flow spreader through a pipe, it is recommended that the pipe be submerged to the extent practical to dissipate as much energy as possible. • For higher inflows (greater than 5 cfs for the 100-yr storm), a Type 1 catch basin shall be positioned in the spreader and the inflow pipe shall enter the catch basin with flows exiting through the top grate. The top of the grate shall be lower than the level spreader plate, or if a notched spreader is used, lower than the bottom of the v-notches. Option A --Anchored Plate • An anchored plate flow spreader must be preceded by a sump having a minimum depth of 8 inches and minimum width of 24 inches. If not otherwise stabilized, the sump area must be lined to reduce erosion and to provide energy dissipation. • The top surface of the flow spreader plate must be level, projecting a minimum of 2 inches above the ground surface of the water quality facility, or V-notched with notches 6 to 10 inches on center and 1 to 6 inches deep (use shallower notches with closer spacing). Alternative designs may also be used if approved by the City. • A flow spreader plate must extend horizontally beyond the bottom width of the facility to prevent water from eroding the side slope. The horizontal extent shall be such that the bank is protected for all flows up to the 100-year flow or the maximum flow that will enter the Water Quality (WQ) facility. • Flow spreader plates must be securely fixed in place. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 28 Chapter 3 • Flow spreader plates may be made of either wood, metal, fiberglass reinforced plastic, or other durable material. If wood, pressure treated 4 by 10-inch lumber or landscape timbers are acceptable. • Anchor posts must be 4-inch square concrete, tubular stainless steel, or other material resistant to decay. Figure V-3-3. Flow Spreader Option A – Anchored Plate S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 29 Chapter 3 Option B --Concrete Sump Box • The wall of the downstream side of a rectangular concrete sump box must extend a minimum of 2 inches above the treatment bed. This serves as a weir to spread the flows uniformly across the bed. • The downstream wall of a sump box must have “wing walls” at both ends. Side walls and returns must be slightly higher than the weir so that erosion of the side slope is minimized. • Concrete for a sump box can be either cast-in-place or precast, but the bottom of the sump must be reinforced with wire mesh for cast-in-place sumps. • Sump boxes must be placed over bases that consists of 4 inches of crushed rock, 5/8-inch minus to help assure the sump remains level. Figure V-3-4. Flow Spreader Option B – Concrete Sump Box S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 30 Chapter 3 Option C --Notched Curb Spreader Notched curb spreader sections must be made of extruded concrete laid side-by-side and level. Typically five “teeth” per four-foot section provide good spacing. The space between adjacent “teeth” forms a v-notch. Figure V-3-5. Flow Spreader Option C – Notched Curb Spreader S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements for Volume V Stormwater Facilities 6 31 Chapter 3 Option D --Through-Curb Ports (Figure V-3-6) Unconcentrated flows from paved areas entering filter strips or continuous inflow biofiltration swales can use curb ports or interrupted curbs (Option E) to allow flows to enter the strip or swale. Curb ports use fabricated openings that allow concrete curbing to be poured or extruded while still providing an opening through the curb to admit water to the water quality facility. Openings in the curb must be at regular intervals but at least every 6 feet (minimum). The width of each curb port opening must be a minimum of 11 inches. Approximately 15 percent or more of the curb section length shall be in open ports, and no port shall discharge more than about 10 percent of the flow. Figure V-3-6. Flow Spreader Option D – Through-Curb Ports Option E --Interrupted Curb Interrupted curbs are sections of curb placed to have gaps spaced at regular intervals along the total width (or length, depending on facility) of the treatment area. At a minimum, gaps must be every 6 feet to allow distribution of flows into the treatment facility before they become too concentrated. The opening must be a minimum of 11 inches. As a general rule, no opening shall discharge more than 10 percent of the overall flow entering the facility. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Pretreatment Volume V 6 32 Chapter 4 Chapter 4 Pretreatment 4.1 Purpose This chapter presents the methods that may be used to provide pretreatment prior to runoff treatment facilities. Pretreatment must be provided in the following applications: • For sand filtration and infiltration Best Management Practices (BMPs) to protect them from excessive siltation and debris; • Where the basic treatment facility or the receiving water may be adversely affected by non-targeted pollutants (e.g., oil), or may be overwhelmed by a heavy load of targeted pollutants (e.g., suspended solids). 4.2 Application Presettling basins are a typical pretreatment BMP used to remove suspended solids. All basic, enhanced, and phosphorus treatment options may be used for pretreatment to reduce suspended solids. A detention pond sized to meet the flow control standard in Volume I may also be used to provide pretreatment for suspended solids removal. 4.3 BMPs BMPs for Pretreatment 4.3.1 BMP T610 Presettling Basin 4.3.1.1 Purpose and Definition A presettling basin provides pretreatment of runoff in order to remove suspended solids, which can impact other runoff treatment BMPs. 4.3.1.2 Application and Limitations Runoff treated by a presettling basin may not be discharged directly to a receiving water; it must be further treated by a basic, enhanced, or phosphorus runoff treatment BMP. 4.3.1.3 Design Criteria 1. A presettling basin shall be designed using analysis techniques for a wetpool or using WWHM. The treatment volume shall be at least 30 percent of the total volume of runoff from the 6-month, 24-hour storm event. 2. If the runoff in the presettling basin will be in direct contact with the soil, it must be lined per the liner requirement in Section 3.4. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Pretreatment Volume V 6 33 Chapter 4 3. The presettling basin shall conform to the following: o The length-to-width ratio shall be at least 3:1. Berms or baffles may be used to lengthen the flowpath. o The minimum depth shall be 4 feet; the maximum depth shall be 6 feet. 4. Inlets and outlets shall be designed to minimize velocity and reduce turbulence. Inlet and outlet structures should be located at extreme ends of the basin in order to maximize particle-settling opportunities. 4.3.1.4 Site Constraints and Setback Requirements Site constraints are any manmade restrictions such as property lines, easements, structures, etc. that impose constraints on development. Constraints may also be imposed from natural features such as requirements in the Auburn City Code. These should also be reviewed for specific application to the proposed development. For Setback Requirements see Section 3.3.1. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 34 Chapter 5 Chapter 5 Infiltration and Bio-infiltration Treatment Facilities 5.1 Purpose This chapter provides site suitability, design, and maintenance criteria for infiltration treatment systems. Infiltration treatment Best Management Practices (BMPs) serve the dual purpose of removing pollutants (TSS, heavy metals, phosphates, and organics) from stormwater and recharging aquifers. The infiltration BMPs described in this chapter include: BMP T710 Infiltration basins BMP T720 Infiltration trenches BMP T730 Bio-infiltration swales 5.2 Application These infiltration and bio-infiltration treatment measures are capable of achieving the performance objectives cited in Chapter 3 for specific treatment menus. In general, these treatment techniques can capture and remove or reduce the target pollutants to levels that will not adversely affect public health or beneficial beneficial uses of surface and groundwater resources. Infiltration treatment systems are typically installed: • As off-line systems, or on-line for small drainages. • As a polishing treatment for street/highway runoff after pretreatment for TSS and oil. • As part of a treatment train. • As retrofits at sites with limited land areas, such as residential lots, commercial areas, parking lots, and open space areas. • With appropriate pretreatment for oil and silt control to prevent clogging. An infiltration basin is preferred, where applicable, and where a trench or bio-infiltration swale cannot be sufficiently maintained. 5.3 Site Suitability The following site suitability criteria (SSC) must be considered. When a site investigation reveals that any of the eight applicable criteria cannot be met, appropriate mitigation measures must be implemented so that the infiltration facility will not pose a threat to safety, health, and the environment. For site selection and design decisions a geotechnical and hydrogeologic report must be prepared by a qualified engineer with geotechnical and hydrogeologic experience, or an equivalent professional acceptable to the City, under the seal of a registered Professional Engineer. The design engineer may utilize a team of certified or registered professionals in soil science, hydrogeology, geology, and other related fields. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 35 Chapter 5 5.3.1 Setback Criteria (SSC-1) Setback requirements are generally required by the City, uniform building code requirements, or other state regulations. Where a conflict between setbacks occurs, the City shall require compliance with the most stringent of the setback requirements from the various codes/regulations. Setback criteria for the various infiltration and dispersion facilities can be found in the design criteria for each BMP in this chapter. Below are conditions that the soils professional must evaluate to determine the need for additional or more stringent setbacks than outlined in this manual. The professional must evaluate: • Potential impacts to drinking water wells, septic tanks or drainfields, and springs used for public drinking water supplies. Minimum setback will be 100 feet. Infiltration facilities upgradient of drinking water supplies and within 1, 5, and 10-year time of travel zones must comply with Health Dept. requirements (Publication # 331-018). • Potential impacts from roadways subject to deicers or herbicides which are likely to be present in the influent to the infiltration system. • Potential impacts to all building foundations in the vicinity of the proposed infiltration facility. Recommend investigating all building foundations: within 100 feet upslope and 20 feet downslope from the facility. • Potential impacts to all property lines within 20 feet of the facility. • Potential impacts to a Native Growth Protection Easement (NGPE); 20 feet. • Potential impacts to the top of slopes >20% and within 50 feet. • On-site and off-site structural stability due to extended subgrade saturation and/or head loading of the permeable layer, including the potential impacts to downgradient properties, especially on hills with known side-hill seeps. 5.3.2 Groundwater Protection Areas (SSC-2) A site is not suitable if the infiltration facility facility will cause a violation of Ecology's Groundwater Quality Standards (See Section 5.3.7 for verification testing guidance). 5.3.3 High Vehicle Traffic Areas (SSC-3) An infiltration BMP may be considered for runoff from areas of industrial activity and the high vehicle traffic areas described below. For such applications sufficient pollutant removal (including oil removal) shall be provided upstream of the infiltration facility to ensure that groundwater quality standards will not be violated and that the infiltration facility is not adversely affected. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 36 Chapter 5 High Vehicle Traffic Areas are: • Commercial or industrial sites subject to an expected average daily traffic count (ADT) 100 vehicles/1,000 ft² gross building area (trip generation), and • Road intersections with an ADT of 25,000 on the main roadway, or 15,000 on any intersecting roadway. 5.3.4 Soil Infiltration Rate/Drawdown Time for Treatment (SSC-4) 5.3.4.1 Infiltration Rates: Short-term and Long-term For treatment purposes, the short-term soil infiltration rate should be 2.4 in/hour, or less, to a depth of 2.5 times the maximum design pond water depth, or a minimum of 6 ft. below the base of the infiltration facility. This infiltration rate is also typical for soil textures that possess sufficient physical and chemical properties for adequate treatment, particularly for soluble pollutant removal (see Section 5.3.6). It is comparable to the textures represented by Hydrologic Groups B and C. Longterm infiltration rates up to 2.0 inches/hour can also be considered, if the infiltration receptor is not a sole-source aquifer, and in the judgment of the site professional, the treatment soil has characteristics comparable to those specified in SSC-6 to adequately control the target pollutants. The long-term infiltration rate should be used for drawdown time and routing calculations. 5.3.4.2 Drawdown Time Refer to Section 5.4 for infiltration rate determination. Document that the 91st percentile, 24-hour runoff volume (as indicated by the Western Washington Hydrology Model [WWHM]) can infiltrate through the infiltration basin surface within 48 hours. This can be calculated using a horizontal projection of the infiltration basin mid-depth dimensions and the estimated long-term infiltration rate. This drawdown restriction is intended to meet the following objectives: • Restore hydraulic capacity to receive runoff from a new storm, • Maintain infiltration rates, • Aerate vegetation and soil to keep the vegetation healthy, and • Enhance the biodegradation of pollutants and organics in the soil. 5.3.5 Depth to Bedrock, Water Table, or Impermeable Layer (SSC-5) The base of all infiltration basins or trench systems shall be 5 feet above the seasonal high-water mark, bedrock (or hardpan) or other low permeability layer. A separation down to 3 feet may be considered if the groundwater mounding analysis, volumetric receptor capacity, and the design of the overflow and/or bypass structures are judged by the site professional to be adequate to prevent overtopping and meet the site suitability criteria specified in this section. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 37 Chapter 5 5.3.6 Soil Physical and Chemical Suitability for Treatment (SSC-6) The soil texture and design infiltration rates should be considered along with the physical and chemical characteristics specified below to determine if the soil is adequate for removing the target pollutants. The following soil properties must be carefully considered in making such a determination: • Cation exchange capacity (CEC) of the treatment soil must be 5 milliequivalents CEC/100 g dry soil (USEPA Method 9081). Consider empirical testing of soil sorption capacity, if practicable. Ensure that soil CEC is sufficient for expected pollutant loadings, particularly heavy metals. CEC values of >5 meq/100g are expected in loamy sands, according to Rawls, et al. Lower CEC content may be considered if it is based on a soil loading capacity determination for the target pollutants that is accepted by the City. • Depth of soil used for infiltration treatment must be a minimum of 18 inches. • Organic Content of the treatment soil (ASTM D 2974): Organic matter can increase the sorptive capacity of the soil for some pollutants. The site professional should evaluate whether the organic matter content is sufficient for control of the target pollutant(s). • Waste fill materials should not be used as infiltration soil media nor should such media be placed over uncontrolled or non-engineered fill soils. Engineered soils may be used to meet the design criteria in this chapter and the performance goals in Chapter 2 and Chapter 3. Field performance evaluation(s), using acceptable protocols, would be needed to determine feasibility and acceptability by the City of Auburn. 5.3.7 Seepage Analysis and Control (SSC-7) Determine whether there would be any adverse effects caused by seepage zones on nearby building foundations, basements, roads, parking lots or sloping sites. 5.3.8 Cold Climate and Impact of Roadway Deicers (SSC-8) For cold climate design criteria (snowmelt/ice impacts) refer to D. Caraco and R. Claytor, “Design Supplement for Stormwater BMPs in Cold Climates”, Center for Watershed Protection, 1997. Potential impact of roadway deicers on potable water wells must be considered in the siting determination. Mitigation measures must be implemented if infiltration of roadway deicers can cause a violation of groundwater quality standards. 5.3.9 Verification Testing of the Completed Facility Verification testing of the completed full-scale infiltration facility is recommended to confirm that the design infiltration parameters are adequate. The site professional should determine the duration and frequency of the verification testing program including the monitoring program for the potentially impacted groundwater. The groundwater monitoring wells installed during site characterization (see 5.4) may be used for this purpose. Long-term (more than two years) in-situ drawdown and confirmatory monitoring of the the infiltration facility would be preferable. The City may require verification testing on a case-by-case basis. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 38 Chapter 5 5.4 Site Characterization Use the following guidelines to determine if the site suitability criteria have been met. 5.4.1 Field Methods used to Determine Subsurface Characterization 5.4.1.1 Test Holes or Pits • Dig test holes or pits to a depth below the base of the infiltration facility of at least 5 times the maximum design depth of ponded water proposed for the infiltration facility, • Conduct pit/hole exploration during the wet season (December 1st through April 30th) to provide accurate groundwater saturation and groundwater information. • Take soil samples (representative samples from each soil type and/or unit within the infiltration receptor) to a depth below the base of the infiltration facility of 2.5 times the maximum design ponded water depth, but not less than 6 feet. o For basins, at least one test pit or test hole per 5,000 ft2 of basin basin infiltrating surface (in no case less than two per basin) is required. o For trenches, at least one test pit or test hole per 50 feet of trench length (in no case less than two per trench) is required. The depth and number of test holes or test pits and samples should be increased if, in the judgment of a licensed engineer with geotechnical expertise (P.E.) or other licensed professional acceptable to the City, the conditions are highly variable and such increases are necessary to accurately estimate the performance of the infiltration system. The exploration program may also be decreased if, in the opinion of the licensed engineer or other professional, the conditions are relatively uniform and the borings/test pits omitted will not influence the design or successful operation of the facility. In high water table sites the subsurface exploration sampling need not be conducted lower than two (2) feet below the groundwater table. • Prepare detailed logs for each test pit or test hole and a map showing the location of the test pits or test holes. Logs must include at a minimum, depth of pit or hole, soil descriptions, depth to water, presence of stratification. At a minimum, soil characterization for each soil unit (soils of the same texture, color, density, compaction, consolidation and permeability) encountered shall include: o Grain-size distribution (ASTM D422 or equivalent AASHTO specification). o Textural class (USDA) (see Volume III, Figure III-2-5). o Percent clay content (include type of clay, if known). o Cation exchange capacity (CEC) and organic matter content for each soil type and strata. Where distinct changes in soil properties occur, to a depth below the base of the facility of at least 2.5 times the maximum design water depth, but not less than 6 feet. Consider if soils are already contaminated, thus diminishing pollutant sorptive capacity (for water quality design only). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 39 Chapter 5 o For soils with low CEC and organic content, deeper characterization of soils may be warranted. o Color/mottling. o Variations and nature of stratification. 5.4.1.2 Infiltration Rate Determination Determine the representative infiltration rate of the unsaturated vadose zone based on field infiltration tests and/or grain size/texture determinations. Field infiltration rates can be determined using the Pilot Infiltration Test (see PIT-Appendix B). Such site testing should be considered to verify infiltration rate estimates based on soil size distribution and/or texture. Infiltration rates may also be estimated based on soil grain-size distributions from test pits or test hole samples. This may be particularly useful where a sufficient source of water does not exist to conduct a pilot infiltration test. As a minimum, one soil grain-size analysis per soil stratum in each test hole shall be performed within 2.5 times the maximum design water depth, but not less than 6 feet. The infiltration rate is needed for routing and sizing purposes and for classifying the soil for treatment adequacy. 5.4.1.3 Infiltration Receptor Infiltration receptor (unsaturated and saturated soil receiving the storm water) characterization should include: • Installation of groundwater monitoring wells. Use at least three per infiltration facility, or three hydraulically connected surface and groundwater features. This will establish a three-dimensional relationship for the groundwater table, unless the highest groundwater level is known to be at least 50 feet below the proposed infiltration facility. The monitoring wells will: o Monitor the seasonal groundwater levels at the site during at least one wet season, and, o Consider the potential for both unconfined and confined aquifers, or confining units, at the site that may influence the proposed infiltration facility as well as the groundwater gradient. Other approaches to determine groundwater levels at the proposed site could be considered if pre-approved by the City, and, o Determine the ambient groundwater quality, if that is a concern. • An estimate of the volumetric water holding capacity of the infiltration receptor soil. This is the soil layer below the infiltration facility and above the seasonal high-water mark, bedrock, hardpan, or other low permeability layer. This analysis should be conducted at a conservatively high infiltration rate based on vadose zone porosity, and the water quality runoff volume to be infiltrated. This, along with an analysis of groundwater movement, will be useful in determining if there are volumetric limitations that would adversely affect drawdown. • Depth to groundwater table and to bedrock/impermeable layers. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 40 Chapter 5 • Seasonal variation of groundwater table based on well water levels and observed mottling. • Existing groundwater flow direction and gradient. • Lateral extent of infiltration receptor. • Horizontal hydraulic conductivity of the saturated zone to assess the aquifer’s ability to laterally transport the infiltrated water. • Impact of the infiltration rate and volume at the project site on groundwater mounding, flow direction, and water table; and the discharge point or area of the infiltrating water. A groundwater mounding analysis shall be conducted at all sites where the depth to seasonal groundwater table or low permeability stratum is less than 15 feet and the runoff to the infiltration facility is from more than one acre. The site professional can consider conducting an aquifer test, or slug test and the type of groundwater mounding analysis necessary at the site. 5.4.2 Design Infiltration Rate Determination Infiltration rates for treatment can be determined using either a correlation to grain size distribution from soil samples, textural analysis, or by in-situ field measurements. Infiltration rate design information shall be prepared and sealed by a licensed engineer or licensed geologist and submitted to the City along with the Stormwater Site Plan. 5.4.2.1 Three Methods for Determining Long-term Infiltration Rate for Sizing the Infiltration Basin, Trench, or Swale For designing the infiltration facility, the site professional should select one of the three methods described below that will best represent the long-term infiltration rate at the site. The long-term infiltration rate should be used for routing and sizing the basin/trench for the maximum drawdown time of 24 hours. Verification testing of the completed facility is strongly encouraged using the criteria described in Section 5.3.9. Method 1 — USDA Soil Textural Classification The infiltration rates provided in Volume III, Table III-2-7 represents rates for homogeneous soil conditions. If more than one soil unit is encountered within 6 feet of the base of the facility, or 2.5 times the proposed maximum water design depth, use the lowest infiltration rate determined from each of the soil units as the representative site infiltration rate. • Use Volume III, Figure III-2-5 (USDA Textural Triangle) to determine the soil textural classification. Only soils passing the #10 sieve may be used to determine the percentages of sand, silt, and clay. • More information on the USDA textural classification can be found in the Soils Survey Manual (U.S. Department of Agriculture, October 1993). • Use the textural classification obtained from Volume III, Figure III-2-5 and Volume III, Table III-2-7 to determine the short and long-term infiltration rates. Treatment site suitability criteria (Section 5.3.4) must be met. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 41 Chapter 5 • Consider alternate correction factors if site conditions warrant. Alternate correction factors require City approval. In no case shall a correction factor less than 2.0 be used. Correction factors higher than those provided in Volume III, Table III-2-7 should be considered for situations where: long-term maintenance will be difficult to implement; where little or no pretreatment is anticipated, where site conditions are highly variable or uncertain, or where soil mottling exists that cannot be fully represented in the soil gradation tests. These situations require the use of best professional judgment by the site engineer and the approval of the City. An operation and maintenance plan and a financial bonding plan may also be required by the City. Use Method 2 if the soil gradation was determined using ASTM D422. Method 2 — ASTM Gradation Testing at Full Scale Infiltration Facilities This method may not be used for soils with a d10 size less than 0.05 mm (U.S. Standard Sieve). The infiltration rates provided in Volume III, Table III-2-8 represent rates for homogeneous soil conditions. If more than one soil unit is encountered within 6 feet of the base of the facility, or 2.5 times the proposed maximum water design depth, use the lowest infiltration rate determined from each of the soil units as the representative site infiltration rate. 1. Determine the long-term infiltration rate using the d10 value obtained from ASTM D422 and Volume III, Table III-2-8. 2. Consider alternate correction factors if site conditions warrant. Alternate correction factors require City approval. 3. Correction factors higher than those provided in Volume III, Table III-2-7 should be considered for situations where: long-term maintenance will be difficult to implement; where little or no pretreatment is anticipated, where site conditions are highly variable or uncertain, or where soil mottling exists that cannot be fully represented in the soil gradation tests. These situations require the use of best professional judgment by the site engineer and the approval of the City. An operation and maintenance plan and a financial bonding plan may also be required by the City. Method 3 -In-situ Infiltration Measurements or Pilot Infiltration Tests (PIT) Where feasible, use in-situ infiltration measurements. Use a procedure such as the Pilot Infiltration Test (PIT) described in Appendix B. As with the previous methods, the infiltration rate obtained from the PIT shall be considered to be a short-term rate. To obtain long-term infiltration rates the short-term rates must be reduced by applying a total correction factor. The total correction factor is the sum of the partial correction factors, presented in Table V-B-17 (Appendix B), which account for site variability, number of tests conducted, degree of long-term maintenance, influent pretreatment/control, and potential for longterm clogging clogging due to siltation and bio-buildup. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 42 Chapter 5 The range of partial correction factors is for general guidance only. The specific partial correction factors used shall be determined based on the professional judgment of the licensed engineer or other site professional considering all issues which may affect the long-term infiltration rate, subject to the approval of the City. Use the following guidance to determine the partial correction factors to apply from Table V-B-17 (Appendix B). • Site variability and number of locations tested. The number of locations tested must represent the subsurface conditions throughout the facility site. If the range of uncertainty is low (for example, conditions are known to be uniform through previous exploration and site geological factors), one pilot infiltration test may be adequate to justify a partial correction factor at the low end of the range. If the level of uncertainty is high, due to highly variable site conditions or limited local testing data, a partial correction factor near the high end of the range may be appropriate. This might be the case where the site conditions are highly variable due to a deposit of ancient landslide debris, or buried stream channels. In these cases, even with many explorations and several pilot infiltration tests, the level of uncertainty may still be high. • Degree of long-term maintenance to prevent siltation and bio-buildup. The standard of comparison here is the long-term maintenance requirements provided in Volume I, Appendix D and any additional requirements by the City. Full compliance with these requirements would be justification to use a partial correction factor at the low end of the range. If there is a high degree of uncertainty that long-term maintenance will be carried out consistently, or if the maintenance plan is poorly defined, a partial correction factor near the high end of the range may be justified. • Degree of influent control to prevent siltation and bio-buildup. A partial correction factor near the high end of the range may be justified under the following circumstances: o If the infiltration facility is located in a shady area where moss or litter fall, buildup from the surrounding vegetation is likely and cannot be easily controlled through long-term maintenance. o If there is minimal pretreatment, and the influent is likely to contain moderately-high TSS levels. The determination of long-term design infiltration rates from in-situ infiltration test data involves a considerable amount of engineering judgment. Therefore, when reviewing or determining the final long-term design infiltration rate, the City may consider the results of both textural analyses and insitu infiltration tests results when available. 5.4.2.2 General Sizing Criteria This information is applicable to infiltration basins, trenches, and bio-infiltration facilities. Size the device by routing 91% of the runoff volume, as predicted by the WWHM through the facility. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 43 Chapter 5 Infiltration facilities for treatment can be located upstream or downstream of detention and can be offline or on-line. • On-line treatment facilities placed upstream or downstream of a detention facility must be sized to infiltrate 91% of the runoff file volume directed to it. • Off-line treatment facilities placed upstream of a detention facility must have a flow splitter designed to send all flows at or below the 15-minute water quality flow rate, as predicted by WWHM, to the treatment facility. The treatment facility must be sized to infiltrate all the runoff sent to it (no overflows from the treatment facility are allowed). • Off-line treatment facilities placed downstream of a detention facility must have a flow splitter designed to send all flows at or below the 2-year flow frequency from the detention pond, as predicted by WWHM, to the treatment facility. The treatment facility must be sized to infiltrate all the runoff sent to it (no overflows from the treatment facility are allowed). 5.4.2.3 General Design Criteria • Slope of the base of the infiltration facility should be < 3 percent. • Spillways/overflow structures – A non-erodible outlet or spillway with a firmly established elevation must be constructed to discharge overflow. Ponding depth, drawdown time, and storage volume are calculated from that reference point. Refer to Volume III, Section 2.3 for overflow structure design details. • For infiltration treatment facilities, side-wall seepage is not a concern if seepage occurs through the same stratum as the bottom of the facility. However, for engineered soils or for soils with very low permeability, the potential to bypass the treatment soil through the side-walls may be significant. In those cases, the side-walls must be lined, either with an impervious liner or with at least 18 inches of treatment soil, to prevent seepage of untreated flows through the side walls. 5.4.2.4 General Construction Criteria • Initially excavate to within 1-foot of the final floor elevation of the infiltration facility. Do not excavate to the final grade until all disturbed areas in the upgradient watershed have been stabilized or protected. Remove all accumulated sediment in the final phase of excavation. • Post-construction, all water must be conveyed through a pretreatment device to prevent sedimentation. • Infiltration facilities should not be used as temporary sediment traps during construction. • Use light-tracked equipment for excavation to avoid compaction of the floor of the infiltration facility. The use of draglines and trackhoes should be considered. The infiltration area should be flagged or marked to keep equipment away. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 44 Chapter 5 5.4.2.5 Maintenance Criteria • Make provision for regular and perpetual maintenance of the infiltration basin/trench, including replacement and/or reconstruction of the treatment infiltration medium. • Include access for operation and maintenance in system design. • Include an operation and maintenance plan. The plan must be approved by the City. • Remove accumulated debris/sediment every 6 months or as needed to prevent clogging, or when water remains in the pond for greater than 24 hours. • Replace or amend the treatment soil as needed to ensure maintaining adequate treatment capacity. 5.4.2.6 Verification of Performance During the first 1 to 2 years of operation, verification testing as specified in Section 5.3.9 is strongly recommended, along with a maintenance program that achieves expected performance levels. Operating and maintaining groundwater monitoring wells is also strongly encouraged. In order to determine compliance with the flow control requirements, the WWHM must be used. 5.5 BMPs for Infiltration and Bio-infiltration Treatment The three BMPs discussed below are recognized currently as effective treatment techniques using infiltration and bio-infiltration. Selection of a specific BMP should be based on the Treatment Facility Menus provided in Chapter 2. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 45 Chapter 5 5.5.1 BMP T710 Infiltration Basins 5.5.1.1 Description Infiltration basins are earthen impoundments used for the collection, temporary storage and infiltration of incoming stormwater runoff. 5.5.1.2 Design Criteria Specific for Basins • Complete a site suitability analysis per Section 5.3. • Provide access for vehicles to easily maintain the forebay (presettling basin) area and not disturb vegetation, or resuspend sediment any more than is absolutely necessary. • The slope of the basin bottom should not exceed 3% in any direction. • Provide a minimum of one foot of freeboard when establishing the design ponded water depth. Freeboard is measured from the rim of the infiltration facility to the maximum ponding level or from the rim down to the overflow point if overflow or a spillway is included. • Establish vegetation on the basin floor and side slopes slopes to prevent erosion and sloughing and to provide additional pollutant removal. Provide erosion protection of inflow points to the basin (e.g., riprap, flow spreaders, energy dissipators (See Chapter 3). Refer to Chapter 7 for recommended vegetation. • Lining material – Basins can be open or covered with a 6 to 12-inch layer of filter material such as coarse sand, or a suitable filter fabric to help prevent the buildup of impervious deposits on the soil surface. A nonwoven geotextile should be selected that will function sufficiently without plugging (see geotextile specifications in Appendix C). The filter layer shall be replaced or cleaned when/if it becomes clogged. • Stabilize and plant embankment, emergency spillways, spoil and borrow areas, and other disturbed areas. Without healthy vegetation the surface soil pores would quickly plug. 5.5.1.3 Maintenance Criteria for Basins • Maintain basin floor and side slopes to promote dense turf with extensive root growth. This enhances infiltration, prevents erosion and consequent sedimentation of the basin floor, and prevents invasive weed growth. Immediately stabilize and revegetate any bare spots. • Vegetation growth should not be allowed to exceed 18 inches in height. Mow the slopes periodically and check for clogging, and erosion. Remove clippings from mowing, weeding and pruning operations. • Seed mixtures should be the same as those recommended in Table V-7-12. The use of slow-growing, stoloniferous grasses will permit long intervals between mowing. Mowing twice a year is generally satisfactory. Fertilizers are not allowed. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 46 Chapter 5 5.5.2 BMP T720 Infiltration Trenches 5.5.2.1 Description Infiltration trenches are generally at least 24 inches wide, and are backfilled with a coarse stone aggregate, allowing for temporary storage of stormwater runoff in the voids of the aggregate material. Stored runoff gradually infiltrates into the surrounding soil. The surface of the trench can be covered with grating and/or consist of stone, gabion, sand, or a grassed covered area with a surface inlet. Perforated rigid pipe of at least 8-inch diameter can also be used to distribute the stormwater in a stone trench. 5.5.2.2 Design Criteria • Complete a site suitability analysis per Section 5.3. • Include an access port or open or grated top for accessibility to conduct inspections and maintenance. • Use clean aggregate with a maximum diameter of 3 inches and a minimum diameter of 1.5 inches to fill trench. Void space for these aggregates should be in the range of 30 to 40 percent. • Line sides of trench with an engineered geotextile material. Geotextile should surround all of the aggregate fill material except for the top one-foot, which is placed over the geotextile. Geotextile fabric with acceptable properties must be carefully selected to avoid plugging (see Appendix C). • The bottom sand or geotextile fabric is optional. • Overflow Channel -Because an infiltration trench is generally used for small drainage areas, an emergency spillway is not necessary. However, a non-erosive overflow channel leading to a stabilized watercourse should be provided. • Trench can be placed under a porous or impervious surface cover to conserve space. • Install an observation well at the lower end of the infiltration trench to check water levels, drawdown time, sediment accumulation, and conduct water quality monitoring. Figure V-5-7 illustrates observation well details. It should consist of a perforated PVC pipe which is 4 to 6 inches in diameter and it should be constructed flush with the ground elevation. For larger trenches a 12-36 inch diameter well can be installed to facilitate maintenance operations such as pumping out the sediment. Cap the top of the well to discourage vandalism and tampering. 5.5.2.3 Construction Criteria • Trench Preparation –Place excavated materials away from the trench sides to enhance trench wall stability. Keep excavated material away from slopes, neighboring property, sidewalks and streets. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 47 Chapter 5 • Stone Aggregate Placement and Compaction – Place the stone aggregate in lifts and compact using plate compactors. As a rule of thumb, a maximum loose lift thickness of 12 inches is recommended. The compaction process ensures geotextile conformity to the excavation sides, thereby reducing potential piping and geotextile clogging, and settlement problems. • Potential Contamination -Prevent natural or fill soils from intermixing with the stone aggregate. Remove all contaminated stone aggregate and replace with uncontaminated stone aggregate. • Overlapping and Covering -Following the stone aggregate placement, fold the geotextile over the stone aggregate to form a 12-inch-minimum longitudinal overlap. When overlaps are required between rolls, overlap the upstream roll a minimum of 2 feet over the downstream roll in order to provide a shingled effect. • Voids behind Geotextile – Avoid voids between the geotextile and excavation sides. Remove boulders or other obstacles from the trench walls. Place natural soils in voids at the most convenient time during construction to ensure geotextile conformity to the excavation sides. Soil piping, geotextile clogging, and possible surface subsidence will be avoided by this remedial process. • Unstable Excavation Sites -Vertically excavated walls may be difficult to maintain in areas where the soil moisture is high or where soft or cohesionless soils predominate. Trapezoidal, rather than rectangular, cross-sections may be needed. 5.5.2.4 Maintenance Criteria • Monitor sediment buildup in the top foot of stone aggregate or the surface inlet. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 48 Chapter 5 5.5.3 BMP T730 Bio-infiltration Swale 5.5.3.1 Description Bio-infiltration swales, also known as Grass Percolation Areas, combine grassy vegetation and soils to remove stormwater pollutants by percolation into the ground. Their pollutant removal mechanisms include filtration, soil sorption, and uptake by vegetative root zones. In general, bio-infiltration swales are used for treating stormwater runoff from roofs, roads and parking lots. Runoff volumes greater than water quality design volume are typically overflowed to the subsurface through an appropriate conveyance facility such as a dry well, or an overflow channel to surface water. Overflows that are directed to a surface water must meet Minimum Requirement #7 or #8 (whichever is applicable). If applicable, see Volume I, Chapter 2. 5.5.3.2 Additional Design Criteria Specific for Bio-infiltration Swales • Complete a site suitability analysis per Section 5.3. • Swale bottom: flat with a longitudinal slope less than 1%. • Maximum ponded level: 6 inches. • The design soil thickness may be reduced to as low as 6 inches if appropriate performance data demonstrates that the vegetated root zone and the natural soil can be expected to provide adequate removal and loading capacities for the target pollutants. The design professional should calculate the pollutant loading capacity of the treatment soil to estimate if there is sufficient treatment soil volume for an acceptable design period. • Other combinations of treatment soil thickness, CEC, and organic content design factors can be considered if it is demonstrated that the soil and vegetation will provide a target pollutant loading capacity and performance level acceptable. • The treatment zone depth must contain sufficient organics and texture to ensure good growth of the vegetation. • If demonstrated that 6 inches of treatment depth is sufficient, the maximum infiltration rate is 1 in/hr. In these cases, all other portions of the Site Suitability Criteria apply. • Use native or adapted grass. • Pretreat to prevent the clogging of the treatment soil and/or growth of the vegetation. • Identify pollutants, particularly in industrial and commercial area runoff, that could cause a violation of Ecology's Groundwater Quality Standards (Chapter 173-200 WAC). Include appropriate mitigation measures (pretreatment, source control, etc.) for those pollutants. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Infiltration and Bio-infiltration Volume V Treatment Facilities 6 49 Chapter 5 Figure V-5-7. Observation Well Details S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 50 Chapter 6 Chapter 6 Sand Filtration Treatment Facilities 6.1 Purpose This chapter presents criteria for the design, construction and maintenance of runoff treatment sand filters. Treatment sand filters are used to collect, treat and remove TSS, phosphorous, and insoluble organics (including oils) from stormwater. Sand filtration options discussed in this Chapter are: Basic Sand Filter Large Sand Filter BMP T810 Sand Filter Vault BMP T820 Linear Sand Filter 6.2 Description A typical sand filtration system consists of a pretreatment facility, flow spreader(s), a sand bed, and the underdrain piping. The sand filter bed includes a geotextile fabric between the sand bed and the bottom underdrain system. An impermeable liner under the facility may also be needed if the filtered runoff requires additional treatment to remove soluble groundwater pollutants, or in cases where additional groundwater protection is mandated. The variations of a sand filter include a basic or large sand filter, sand filter with level spreader, sand filter vault, and linear sand filter. Figures V-6-8 through V-6-15 provide examples of various sand filter configurations. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 51 Chapter 6 Source: City of Austin, TX Filtered Outflow (Route through detention basin) Figure V-6-8. Sand Filtration Basin Preceded by Presettling Basin (Variation of a Basic Sand Filter) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 52 Chapter 6 Figure V-6-9. Sand Filter with a Pretreatment Cell (top view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 53 Chapter 6 Figure V-6-10. Sand Filter with a Pretreatment Cell (side view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 54 Chapter 6 Figure V-6-11. Sand Filter with Level Spreader (top view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 55 Chapter 6 Figure V-6-12. Sand Filter with Level Spreader (side view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 56 Chapter 6 6.3 Applications and Limitations Sand filtration can be used in most residential, commercial, and industrial developments where debris, heavy sediment loads, and oils and greases will not clog or prematurely overload the sand, or where adequate pretreatment is provided for these pollutants. Pretreatment is necessary to reduce velocities to the sand filter and remove debris, floatables, large particulate matter, and oils. In high water table areas, adequate drainage of the sand filter may require additional engineering analysis and design considerations. An underground filter should be considered in areas subject to freezing conditions. (Urbonas, 1997) 6.4 Site Suitability The following site characteristics should be considered in siting a sand filtration system: • Space availability, including the space needed for a presettling basin. • Sufficient hydraulic head, at least 4 feet from inlet to outlet. • Adequate Operation and Maintenance capability including accessibility for O&M. • Sufficient pretreatment of oil, debris and solids in the tributary runoff. 6.5 Design Criteria 6.5.1 Objective The objective is to capture and treat 91% of the total runoff volume (95% for large sand filters) as predicted by the Western Washington Hydrology Model (WWHM). 6.5.2 Sand Filter Sizing Sand filter design criteria are as follows: 1. The design hydraulic conductivity shall be 1 in/hr. 2. On-line sand filters must NOT be placed upstream of a detention facility. This is to prevent exposure of the sand filter surface to high flow rates that could cause loss of media and previously removed pollutants. 3. On-line sand filters placed downstream of a detention facility must be sized using WWHM to filter 91% of the runoff volume. 4. Off-line sand filters placed upstream of a detention facility must have a flow splitter designed to send all flows at or below the 15-minute water quality flow rate, as predicted by WWHM to the sand filter. The sand filter must be sized to filter all the runoff sent to it (no overflows from the treatment facility should occur). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 57 Chapter 6 5. Off-line sand filters placed downstream of a detention facility must have a flow splitter designed to send all flows at or below the 2-year frequency peak flow as predicted by WWHM, from the detention facility to the treatment facility. The treatment facility must be sized to filter all the runoff sent to it (no overflows from the treatment facility should occur). 6. Include an overflow in the design. The overflow height shall be at the maximum hydraulic head of the water above the sand bed. 7. Pretreat runoff to be treated by the sand filter (e.g., presettling basin, etc. depending on pollutants) to remove debris and other solids, and oil from high use sites. 8. Design inlet bypass and flow spreading structures (e.g., flow spreaders, weirs or multiple orifice openings) to capture the applicable design flow rate, minimize turbulence and to spread the flow uniformly across the surface of the sand filter. Install stone riprap or other energy dissipation devices to prevent gouging of the sand medium and to promote uniform flow. Include emergency spillway or overflow structures (see Volume III). 9. Include underdrain piping in sand filter design. Types of underdrains include a central collector pipe with lateral feeder pipes; or a geotextile drain strip in an 8-inch gravel backfill or drain rock bed; or longitudinal pipes in an 8-inch gravel backfill or drain rock with a collector pipe at the outlet end. • Upstream of detention, underdrain piping shall be sized to handle double the two-year return frequency flow indicated by the WWHM (the doubling factor is a factor of safety). Downstream of detention the underdrain piping shall be sized for the two-year return frequency flow indicated by the WWHM. In both instances there shall be at least one foot of hydraulic head above the invert of the upstream end of the collector pipe. • Internal diameters of underdrain pipes shall be a minimum of six inches having two rows of ½-inch holes spaced 6 inches apart longitudinally (maximum), with rows 120 degrees apart (laid with holes downward). Maximum perpendicular distance between two feeder pipes must be 15 feet. All piping is to be schedule 40 PVC or greater wall thickness. Drain piping could be installed in basin and trench configurations. Other equivalent underdrains can be used. • Main collector underdrain pipe shall be at a slope of 0.5 percent minimum. • A geotextile fabric (specifications in Appendix C) must be used between the sand layer and drain rock or gravel and placed so that 1-inch of drain rock/gravel is above the fabric. Drain rock shall be 0.75-1.5 inch rock or gravel backfill, washed free of clay and organic material. 10. Provide cleanout wyes with caps or junction boxes at both ends of the collector pipes. Extend cleanouts to the surface of the filter. Provide a valve box for access to the cleanouts. Provide access for cleaning all underdrain piping. This may consist of installing cleanout ports that tee into the underdrain system and surface above the top of the sand bed. To facilitate maintenance of the sand filter an inlet shutoff/bypass valve is recommended. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 58 Chapter 6 11. Sand specification: The sand in a filter must meet the size gradation (by weight) given in Table V-6-7. The contractor must obtain a grain size analysis from the supplier to certify that the No. 100 and No. 200 sieve requirements are met. Table V-6-7. Sand Specifications U.S. Sieve Number Percent Passing 4 95-100 8 70-100 16 40-90 30 25-75 50 2-25 100 <4 200 <2 Source: King County Surface Water Design Manual, September 1998 12. Impermeable Liners for Sand Bed Bottom: Impermeable liners are generally required for soluble pollutants such as metals and toxic organics and where the underflow could cause problems with structures. Impermeable liners may be made of clay, concrete or geomembrane. Clay liners shall have a minimum thickness of 12 inches and meet the specifications given in Table V-6-8. Table V-6-8. Clay Liner Specifications Property Test Method Unit Specification Permeability ASTM D-2434 cm/sec 1 x 10-6 max. Plasticity Index of Clay ASTM D-423 & D-424 percent Not less than 15 Liquid Limit of Clay ASTM D-2216 percent Not less than 30 Clay Particles Passing ASTM D-422 percent Not less than 30 Clay Compaction ASTM D-2216 percent 95% of Standard Proctor Density Source: City of Austin, 1988 • If a geomembrane liner is used it shall have a minimum thickness of 30 mils and be ultraviolet light resistant. The geomembrane liner shall be protected from puncture, tearing, and abrasion by installing geotextile fabric on the top and bottom of the geomembrane. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 59 Chapter 6 • Concrete liners may also be used for sedimentation chambers and for sedimentation and sand filtration basins less than 1,000 square feet in area. Concrete shall be 5 inches thick Class A or better and shall be reinforced by steel wire mesh. The steel wire mesh shall be 6 gauge wire or larger and 6-inch by 6-inch mesh or smaller. An "Ordinary Surface Finish" is required. When the underlying soil is clay or has an unconfined compressive strength of 0.25 ton per square foot or less, the concrete shall have a minimum 6-inch compacted aggregate base. This base must consist of coarse sand and river stone, crushed stone or equivalent with diameter of 0.75-to 1-inch. • If an impermeable liner is not required then a geotextile fabric liner shall be installed that retains the sand and meets the specifications listed in Appendix C unless the basin has been excavated to bedrock. bedrock. • If an impermeable liner is not provided, then an analysis shall be made of possible adverse effects of seepage zones on groundwater, and near building foundations, basements, roads, parking lots and sloping sites. Sand filters without impermeable liners shall not be built on fill sites and shall be located at least 20-feet downslope and 100-feet upslope from building foundations. 13. Include an access ramp with a slope not to exceed 7H:1V, or equivalent, for maintenance purposes at the inlet and the outlet of a surface filter. 14. Side slopes for earthen/grass embankments shall not exceed 3H:1V to facilitate mowing. 15. There shall be at least 2 feet clearance between the seasonal high groundwater level and the bottom of the sand filter. 6.6 Construction Criteria • The sand filter shall not be placed into service until site construction is complete and the site is stabilized. • Place sand in a uniform thickness and compact using a water settling method. Settling shall be accomplished by flooding the sand with 10-15 gallons of water per cubic foot of sand. After flooding, the sand shall be smoothed and leveled. 6.7 Maintenance Criteria Inspections of sand filters and pretreatment systems shall be conducted every 6 months and after storm events as needed during the first year of operation, and annually thereafter. Maintenance suggestions include: • Remove accumulated silt and debris on top of the sand filter when depth exceeds 1/2-inch. Scrape the silt off during dry periods with steel rakes or other devices. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 60 Chapter 6 • Frequent overflow or slow drawdown are indicators of plugging problems. A sand filter shall empty in 24 hours following a storm event (24 hours for the pre-settling chamber), depending on the ponding depth over the filter bed surface. If the hydraulic conductivity drops to 1-inch per hour, corrective action is needed. Examples include: o Scraping the top layer of fine-grain sediment accumulation (mid-winter scraping is suggested) o Removal of thatch o Aerating the filter surface o Tilling the filter surface (late-summer rototilling is suggested) o Replacing the top 4 inches of sand. o Inspecting geotextiles for clogging. • Rapid drawdown in the sand bed (greater than 12 inches per hour) indicates shortcircuiting of the filter. Inspect the periphery of the filter bed and cleanouts on the underdrain pipes for leakage. • Drawdown tests for the sand bed shall be conducted every two years. These tests can be conducted by allowing the filter to fill (or partially fill) during a storm event, then measuring the decline in water level over a 4-8 hour period. An inlet and an underdrain outlet valve would be necessary to conduct such a test. • Formation of rills and gullies on the surface of the filter indicates improper function of the inlet flow spreader, or poor sand compaction. Check for accumulation of debris on or in the flow spreader and refill rills and gullies with sand. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 61 Chapter 6 6.7.1 BMP T810 Sand Filter Vault 6.7.1.1 Description: (Figure V-6-13 and Figure V-6-14) A sand filter vault is similar to an open sand filter except that the sand layer and underdrains are installed below grade in a vault. It consists of presettling and sand filtration cells. 6.7.1.2 Applications and Limitations • Use where space limitations preclude above ground facilities • Not suitable where high water table and heavy sediment loads are expected • An elevation difference of 4 feet between inlet and outlet is needed 6.7.1.3 Additional Design Criteria for Vaults • Optimize sand inlet flow distribution with minimal sand bed disturbance. A maximum 8-inch distance between the top of the spreader and the top of the sand bed is required. Flows may enter the sand bed by spilling over the top of the wall into a flow spreader pad or alternatively a pipe and manifold system may be used. Any pipe and manifold system must retain the required dead storage volume in the first cell, minimize turbulence, and be readily maintainable. • If an inlet pipe and manifold system is used, the minimum pipe size shall be 8 inches. Multiple inlets are required to minimize turbulence and reduce local flow velocities. • Provide erosion protection along the first foot of the sand bed adjacent to the spreader. Geotextile fabric secured on the surface of the sand bed, or equivalent method, may be used. • Design the presettling cell for sediment collection and removal. Use a V-shaped bottom, removable bottom panels, or equivalent sludge handling system. Provide one-foot of sediment storage in the presettling cell. • Seal the pre-settling chamber to trap oil and trash. This chamber is usually connected to the sand filtration chamber using a pipe with an inverted elbow to protect the filter surface from oil and trash. • If a retaining baffle is necessary for oil/floatables in the presettling cell, it must must extend at least one foot above to one foot below the design flow water level. Provide provision for the passage of flows in the event of plugging. Provide access opening and ladder on both sides of the baffle. • To prevent anoxic conditions, provide a minimum of 24 square feet of ventilation grate for each 250 square feet of sand bed surface area. For sufficient distribution of airflow across the sand bed, grates may be located in one area if the sand filter is small, but placement at each end is preferred. Small grates may also be dispersed over the entire sand bed area. • Sand filter vaults must conform to the materials and structural suitability criteria specified for wet vaults in Chapter 8. • Provide a sand filter inlet shutoff/bypass valve for maintenance S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 62 Chapter 6 • A geotextile fabric over the entire sand bed may be installed that is flexible, highly permeable, three-dimensional matrix, and adequately secured. This is useful in trapping trash and litter. Figure V-6-13. Sand Filter Vault (top view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 63 Chapter 6 Figure V-6-14. Sand Filter Vault (side view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 64 Chapter 6 6.7.2 BMP T820 Linear Sand Filter 6.7.2.1 Description Linear sand filters are typically long, shallow, two-celled, rectangular vaults. The first cell is designed for settling coarse particles, and the second cell contains the sand bed. Stormwater enters the second cell via a weir section that also functions as a flow spreader. Figure V-6-15 illustrates a linear sand filter. 6.7.2.2 Application and Limitations • Applicable in long narrow spaces such as the perimeter of a paved surface. • As a part of a treatment train such as downstream of a filter strip, upstream of an infiltration system, or upstream of a wet pond or a biofilter for oil control. • To treat small drainages (less than 2 acres of impervious area). • To treat runoff from high-use sites for TSS and oil/grease removal, if applicable. 6.7.2.3 Additional Design Criteria for Linear Sand Filters • Divide the two cells by a divider wall that is level and extends a minimum of 12 inches above the sand bed. • Stormwater may enter the sediment cell by sheet flow or a piped inlet. • The width of the sand cell must be 1-foot minimum to 15 feet maximum. • The sand filter bed must be a minimum of 12 inches deep and have an 8-inch layer of drain rock with perforated drainpipe beneath the sand layer. • The drainpipe must be 6-inch diameter minimum and be wrapped in geotextile and sloped a minimum of 0.5 percent to promote positive drainage. • Maximum sand bed ponding depth: 12 inches. • Must be vented as described above for sand filter vaults. • Linear sand filters must conform to the materials and structural suitability criteria specified for wet vaults described in Chapter 8. • Sediment cell width shall be selected based on sand filter width as follows: Sand filter width, (w) inches 12-24 24-48 48-72 72+ Sediment cell width, inches 12 18 24 w/3 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Sand Filtration Treatment Facilities Volume V 6 65 Chapter 6 Figure V-6-15. Linear Sand Filter S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 66 Chapter 7 Chapter 7 Biofiltration Treatment Facilities 7.1 Purpose This chapter addresses five Best Management Practices (BMPs) that are classified as biofiltration treatment facilities. Biofilters are vegetated treatment systems (typically grass) that remove pollutants by means of sedimentation, filtration, soil sorption, and/or plant uptake. They are typically configured as swales or flat filter strips. The BMPs discussed in this chapter are designed to remove low concentrations and quantities of total suspended solids (TSS), heavy metals, petroleum hydrocarbons, and/or nutrients from stormwater. 7.2 Applications A biofilter can be used as a basic treatment BMP for stormwater runoff from roadways, driveways, parking lots, and highly impervious ultra-urban areas or as the first stage of a treatment train. In cases where hydrocarbons, high TSS concentrations, or debris would be present in the runoff, such as high-use sites, a pretreatment system for those components is necessary. Placement of the biofilter in an off-line location is preferred to avoid flattening of the vegetation and the erosive effects of high flows. 7.3 Site Suitability The following factors must be considered for determining site suitability: • Accessibility for operation and maintenance. • Suitable growth environment (soil, exposure to sunlight, etc.) for the vegetation. • Adequate siting for a pre-treatment facility if high petroleum hydrocarbon levels (oil/grease) or high TSS loads could impair treatment capacity or efficiency. 7.4 Best Management Practices The following five Biofiltration Treatment Facilities BMPs are discussed in this chapter: BMP T910 – Basic Biofiltration Swale BMP T920 – Wet Biofiltration Swale BMP T930 – Continuous Inflow Biofiltration Swale BMP T940 – Basic Filter Strip & Compost-Amended Filter Strip BMP T950 – Narrow Area Filter Strip S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 67 Chapter 7 7.4.1 BMP T910 Basic Biofiltration Swale 7.4.1.1 Description: Biofiltration swales are typically shaped as a trapezoid or a parabola in cross section as shown in Figure V-7-16 and Figure V-7-17. Figure V-7-16. Typical Swale Section 7.4.1.2 Design Criteria: • Size the swale using sizing criteria specified in Table V-7-9. Minimum length shall be 100 feet. • Check the hydraulic capacity/stability using Qmax. • Select a vegetation cover suitable for the site. Refer to Table V-7-12 through Table V-7-14. • Install level spreaders (minimum 1 inch gravel) at the head of all swales, and every 50 feet in swales of 4 feet width. Include sediment cleanouts (weir, settling basin, or equivalent) at the head of the biofilter as needed. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 68 Chapter 7 • Use energy dissipaters (such as quarry spalls or riprap) for increased downslopes. • A minimum of ten feet (10’) shall be provided between the outside edge of the bioswale and any property line or obstruction that would impede maintenance. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 69 Chapter 7 Source: Livingston, et al, 1984 Figure V-7-17. Geometric Formulas for Common Swale Shapes S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 70 Chapter 7 Table V-7-9. Sizing Criteria Design parameter BMP T 910-Biofiltration swale BMP T 940-Filter strip Longitudinal Slope 0.015 -0.0251 0.01 -0.15 Maximum velocity 1 ft /sec @K2 multiplied by the WQ design flow rate 0.5 ft /sec @K multiplied by the WQ design flow rate Maximum velocity for channel stability3 3 ft/sec ---Maximum water depth4 2”-if mowed frequently; 4” if mowed infrequently 1-inch max. Manning coefficient (0.2 – 0.3)5 (0.24 if mowed infrequently) 0.35 (0.45 if compost amended, or mowed to maintain grass height 4”) Bed width (bottom) (2 -10 ft)6 ---Freeboard height 0.5 ft ---Minimum hydraulic residence time at K multiplied by Water Quality Design Flow Rate 9 minutes (18 minutes for continuous inflow) 9 minutes Minimum length 100 ft Sufficient to achieve hydraulic residence time in the filter strip Maximum sideslope 3 H:1 V 4H:1V preferred Inlet edge 1” lower than contributing paved area Max. tributary drainage flowpath ---150 feet Max. longitudinal slope of contributing area ---0.05 (steeper than 0.05 need upslope flow spreading and energy dissipation) Max. lateral slope of contributing area ---0.02 (at the edge of the strip inlet) 1 For swales, if the slope is less than 1.5% install an underdrain using a perforated pipe, or equivalent. Amend the soil if necessary to allow effective percolation of water to the underdrain. Install the low-flow drain 6-inches deep in the soil. Slopes greater than 2.5% need check dams (riprap) at vertical drops of 12-15 inches. Underdrains can be made of 6-inch Schedule 40 PVC perforated pipe or equivalent with 6” of drain gravel on the pipe. The gravel and pipe must be enclosed by geotextile fabric (see Figure V-7-19 and Figure V-7-20). 2 K=A ratio of the peak 10-minunte flow predicted by SBUH to the water quality design flow rate estimated using the WWHM. The value of K for off-line systems is 3.5, and for on-line systems is 2.0 in the City of Auburn. 3 Maximum flowrate for channel stability shall be the 100-year, 24-hour discharge (Q100) calculated with WWHM using a 15-minute time step. If an hourly time step is used, multiply the Q100 by 1.6. 4 Below the design water depth install an erosion control blanket, at least 4” of topsoil, and the selected biofiltration mix. Above the water line use a straw mulch or sod. 5 This range of Manning’s n can be used in the equation; b = Qn/1.49y(1.67) s(0.5) – Zy with wider bottom width b, and lower depth, y, at the same flow. This provides the designer with the option of varying the bottom width of the swale depending on space limitations. Designing at the higher n within this range at the same flow decreases the hydraulic design depth, thus placing the pollutants in closer contact with the vegetation and the soil. 6 For swale widths up to 16 feet the cross-section can be divided with a berm (concrete, plastic, compacted earthfill) using a flow spreader at the inlet (Figure V-7-21). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 71 Chapter 7 7.4.1.3 Bypass Guidance Most biofiltration swales are currently designed to be on-line facilities. However, an off-line design is possible. Swales designed in an off-line mode should not engage a bypass until the flow rate exceeds a value determined by multiplying Q, the off-line water quality design flow rate predicted by the WWHM, by 3.5 for off-line systems and 2.0 for on-line systems. This modified design flow rate is an estimate of the design flow rate determined by using SBUH procedures. Ecology’s intent is to maintain recent biofiltration sizing recommendations until more definitive information is collected concerning bioswale performance. The only advantage of designing a swale to be off-line is that the stability check, which may make the swale larger, is not necessary. 7.4.1.4 Sizing Procedure for Biofiltration Swales Preliminary Steps P.1 Determine the water quality design flow rate (Q) in 15-minute time steps using WWHM. P.2 Establish the longitudinal slope of the proposed biofilter. P.3 Select an appropriate vegetated cover for the site. Refer to Table V-7-12 through Table V-7-14. Design Steps D.1 Select the type of vegetation and depth of flow (based on frequency of mowing and type of vegetation). D.2 Select a value of Manning’s n. D.3 Select swale shape. D.4 Use a variation on Manning’s equation to solve for bottom width, b. b 2.5Qn 1.49y s Zy 1.67 0.5 − Where: Q = Water Quality Design flow rate in 15-minute time steps based on WWHM, (ft³/s, cfs) n = Manning's n (dimensionless) s = Longitudinal slope as a ratio of vertical rise/horizontal run (dimensionless) y = depth of flow (ft) b = bottom width of trapezoid (ft) For a trapezoid, select a side slope Z of at least 3. Compute b and then top width T, where T = b + 2yZ. NOTE: Adjustment factor of 2.5 accounts for the differential between Water Quality design flow rate and the SBUH design flow. This equation is used to estimate an initial crosssectional area. It does not affect the overall biofiltration swale size. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 72 Chapter 7 If b for a swale is greater than 10 ft, either investigate how Q can be reduced, divide the flow by installing a low berm, or arbitrarily set b = 10 ft and continue with the analysis. For other swale shapes refer to Figure V-7-17. D.5 Compute A A Ty rectangle = or Atrapezoid = by + Zy2 Afilter strip = Ty Where: A = cross-sectional area (ft²) T = top width of trapezoid or width of a rectangle (ft) y = depth of flow (ft) b = bottom width of trapezoid (ft) Z = side slope D.6 Compute the flow velocity at design flow rate: V = K (Q/A) A = cross-sectional area (ft2) K = A ratio of the peak 10-minute flow predicted by SBUH to the water quality design flow rate estimated using the WWHM. The value of K for off-line systems is 3.5 and for on-line systems is 2.0 Q = water quality design flow rate in 15-minute time steps based on WWHM. If V >1.0 ft/sec (or V>0.5 ft/sec for a filter strip), repeat steps D-1 to D-6 until the condition is met. A velocity greater than 1.0 ft/sec was found to flatten grasses, thus reducing filtration. A velocity lower than this maximum value will allow a 9-minute hydraulic residence time criterion in a shorter biofilter. If the value of V suggests that a longer biofilter will be needed than space permits, investigate how Q can be reduced (e.g., use of low impact development BMPs), or increase y and/or T (up to the allowable maximum values) and repeat the analysis. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 73 Chapter 7 D.7 Compute the swale length (L, ft) L = Vt (60 sec/min) Where: t = hydraulic residence time (min) V = flow velocity Use t = 9 minutes for this calculation (use t = 18 minutes for a continuous inflow biofiltration swale). If a biofilter length is greater than the space permits, follow the advice in step 6. If a length less than 100 feet results from this analysis, increase it to 100 feet, the minimum allowed. In this case, it may be possible to save some space in width and still meet all criteria. This possibility can be checked by computing V in the 100 ft biofilter for t = 9 minutes, recalculating A (if V < 1.0 ft/sec) and recalculating T. D.8 If there are space constraints, the local government and the project proponent should consider the following solutions (listed in order of preference): a. Divide the site drainage to flow to multiple biofilters. b. Use infiltration to provide lower discharge rates to the biofilter (only if the Site Suitability Criteria in Section 5.3 of this volume are met). c. Increase vegetation height and design depth of flow (note: the design must ensure that vegetation remains standing during design flow). d. Reduce the developed surface area to gain space for biofiltration. e. Increase the longitudinal slope. f. Increase the side slopes. g. Nest the biofilter within or around another BMP. Stability Check Steps The stability check must be performed for the combination of highest expected flow and least vegetation coverage and height. A check is not required for biofiltration swales that are located "offline" from the primary conveyance/detention system. Maintain the same units as in the biofiltration capacity analysis. The maximum permissible velocity for erosion prevention (Vmax) is 3 feet per second. S.1 Perform the stability check for the 100-year, return frequency flow using 15-minute time steps using WWHM. The designer can use the WWHM 100-100-yr. hourly peak flows times an adjustment factor of 1.6 to approximate peak flows in 15-minute time steps. S.2 Estimate the vegetation coverage ("good" or "fair") and height on the first occasion that the biofilter will receive flow, or whenever the coverage and height will be least. Avoid flow introduction during the vegetation establishment period by timing planting. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 74 Chapter 7 S.3 Estimate the degree of retardance from Table V-7-10. When uncertain, be conservative by selecting a relatively low degree of retardance. Table V-7-10. Stability Check Steps (SC) Guide for Selecting Degree of Retardance Coverage Average Grass Height (inches) Degree of Retardance Good ^ 2 E. Very Low 2-6 D. Low 6-10 C. Moderate 11-24 B. High 30 A. Very High Fair ^ 2 E. Very Low 2-6 D. Low 6-10 D. Low 11-24 C. Moderate 30 B. High * See Chow (1959), In addition, Chow recommended selection of retardance C for a grass-legume mixture 6-8 inches high and D for a mixture 4-5 inches high. No retardance recommendations have appeared for emergent wetland species. Therefore, judgment must be used. Since these species generally grow less densely than grasses, using a “fair” coverage would be a reasonable approach. S.4 Select a trial Manning's n for the high flow condition. The minimum value for poor vegetation cover and low height (possibly, knocked from the vertical by high flow) is 0.033. A good initial choice under these conditions is 0.04. S.5 Refer to Figure V-7-18 to obtain a first approximation for VR. S.6 Compute hydraulic radius, R, from VR in Figure V-7-18 and a Vmax in Table V-7-11. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 75 Chapter 7 Source: Livingston, et al, 1984 VR (feet 2 /second) Figure V-7-18. The Relationship of Manning’s n with VR for Various Degrees of Flow Retardance (A-E) Table V-7-11. Guide to Selecting Maximum Permissible Swale Velocities for Stability* Max Velocity – ft/sec (m/sec) Cover Slope (percent) Erosion-Resistant Soils Easily Eroded Soils Kentucky bluegrass Tall fescue 0-5 6 (1.8) 5 (1.5) Kentucky bluegrass Ryegrasses Western wheatgrass 5-10 5 (1.5) 4 (1.2) 0-5 5 (1.5) 4 (1.2) Grass-legume mixture 5-10 4 (1.2) 3 (0.9) Red fescue 0-5 3 (0.9) 2.5 (0.8) Redtop 5-10 Not recommended Not recommended * Adapted from Chow (1959), Livingston et al (1984), and Goldman et al (1986) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 76 Chapter 7 S.7 Use Manning’s equation to solve for the actual VR. S.8 Compare the actual VR from step S.7 and first approximation from step S.5. If they do not agree within 5 percent, repeat steps S.4 to S.8 until acceptable agreement is reached. If n<0.033 is needed to get agreement, set n = 0.033, repeat step S.7, and then proceed to step S.9. S.9 Compute the actual V for the final design conditions: S.10 Check to be sure V < Vmax of 3 feet/second. S.11 Compute the required swale cross-sectional area, A, for stability: S.12 Compare the A, computed in step S.11 of the stability analysis, with the A from the biofiltration capacity analysis (step D.5). If less area is required for stability than is provided for capacity, the capacity design is acceptable. If not, use A from step S.11 of the stability analysis and recalculate channel dimensions. S.13 Calculate the depth of flow at the stability check design flow rate condition for the final dimensions and use A from step S.11. S.14 Compare the depth from step S.13 to the depth used in the biofiltration capacity design (Step D.1). Use the larger of the two and add 0.5 ft. of freeboard to obtain the total depth (yt) of the swale. Calculate the top width for the full depth using the appropriate equation. SC.15 Recalculate the hydraulic radius: (use b from Step D.4 calculated previously for biofiltration capacity, or Step S.12, as appropriate, and yt = total depth from Step S.14) SC.16 Make a final check for capacity based on the stability check design storm (this check will ensure that capacity is adequate if the largest expected event coincides with the greatest retardance). Use Equation 1, a Manning's n selected in step D.2, and the calculated channel dimensions, including freeboard, to compute the flow capacity of the channel under these conditions. Use R from step SC-14, above, and A = b(yt) + Z(yt)² using b from Step D.4, D.15, or S.12 as appropriate. If the flow capacity is less than the stability check design storm flow rate, increase the channel cross-sectional area as needed for this conveyance. Specify the new channel dimensions. Completion Step Review all of the criteria and guidelines for biofilter planning, design, installation, and operation above and specify all of the appropriate features for the application. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 77 Chapter 7 Figure V-7-19. Biofiltration Swale Underdrain Detail Figure V-7-20. Biofiltration Swale Low-Flow Drain Detail S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 78 Chapter 7 Dividing Berm Height = Design Flow Depth (y ) + 2” (min.) Figure V-7-21. Swale Dividing Berm 7.4.1.5 Soil Criteria • Use the following list as a guide for choosing appropriate soils for the biofiltration swale. Use at least 8-inches of the following top soil mix: o Sandy loam 60-90% o Clay 0-10% o Composted organic matter, (excluding animal waste, toxics) 10-30% • Use compost amended soil where practicable. • Till to at least 8-inch depth. • For longitudinal slopes of < 2 percent use more sand to obtain more infiltration. • If groundwater contamination is a concern, seal the bed with clay or a geomembrane liner. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 79 Chapter 7 7.4.1.6 Vegetation Criteria • See Table V-7-12 through Table V-7-14 for recommended grasses, wetland plants, and groundcovers. • Select fine, turf-forming, water-resistant grasses where vegetative growth and moisture will be adequate for growth. • Irrigate if moisture is insufficient during dry weather season. • Use sod with low clay content and where needed to initiate adequate vegetative growth. Preferably sod should be laid to a minimum of one-foot vertical depth above the swale bottom. • Consider sun/shade conditions for adequate vegetative growth and avoid prolonged shading of any portion not planted with shade tolerant vegetation. • Stabilize soil areas upslope of the biofilter to prevent erosion. • Fertilizing a biofilter shall not be allowed. 7.4.1.7 Construction Criteria • Do not put swale into operation until exposed soil in contributing drainage area is stabilized. • Keep erosion and sediment control measures in place until swale vegetation is established. • Avoid compaction during construction. • Grade biofilters to attain uniform longitudinal and lateral slopes. 7.4.1.8 Maintenance Criteria • Inspect biofilters at least once every 6 months, preferably during storm events, and also after storm events of > 0.5 inch rainfall/24 hours. Maintain adequate grass growth and eliminate bare spots. • Mow grasses, if needed for good growth. Typically maintain at 4 – 9 inches but not below design flow level. • Remove sediment as needed at head of the swale if grass growth is inhibited in greater than 10 percent of the swale, or if the sediment is blocking the distribution and entry of the water. • Remove leaves, litter, and oily materials, and re-seed or resod, and regrade, as needed. Clean curb cuts and level spreaders as needed. Prevent scouring and soil erosion in the biofilter. If flow channeling occurs, regrade and reseed the biofilter, as necessary. • Maintain access to biofilter inlet, outlet, and to mowing (Figure V-7-22). • If a swale is equipped with underdrains, vehicular traffic on the swale bottom (other than grass mowing equipment) shall be avoided to prevent damage to the drainpipes. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 80 Chapter 7 Table V-7-12. Grass Seed Mixes Suitable for Biofiltration Swale Treatment Areas Mix 1 Mix 2 75-80 percent tall or meadow fescue 60-70 percent tall fescue 10-15 percent seaside/colonial bentgrass 10-15 percent seaside/colonial bentgrass 5-10 percent redtop 10-15 percent meadow foxtail 6-10 percent alsike clover 1-5 percent marshfield big trefoil 1-6 percent redtop Note: All percentages are by weight, based on Briargreen, Inc. Table V-7-13. Groundcovers & Grasses Suitable for the Upper Side Slopes of a Biofiltration Swale in Western Washington Groundcovers kinnikinnick* Arctostaphylos uva-ursi Epimedium Epimedium grandiflorum creeping forget-me-not Omphalodes verna --Euonymus lanceolata yellow-root Xanthorhiza simplissima --Genista white lawn clover Trifolium repens white sweet clover* Melilotus alba -------Rubus calycinoides strawberry* Fragaria chiloensis broadleaf lupine* Lupinus latifolius Grasses (drought-tolerant, minimum mowing) dwarf tall fescues Festuca spp. (e.g., Many Mustang, Silverado) hard fescue Festuca ovina duriuscula (e.g., Reliant, Aurora) tufted fescue Festuca amethystina buffalo grass Buchloe dactyloides red fescue* Festuca rubra tall fescue grass* Festuca arundinacea blue oatgrass Helictotrichon sempervirens * Good choices for swales with significant periods of flow, such as those downstream of a detention facility. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 81 Chapter 7 Table V-7-14. Recommended Plants for Wet Biofiltration Swale Common Name Scientific Name Spacing (on center) Shortawn foxtail Alopecurus aequalis seed Water foxtail Alopecurus geniculatus seed Spike rush Eleocharis spp. 4 inches Slough sedge* Carex obnupta 6 inches or seed Sawbeak sedge Carex stipata 6 inches Sedge Carex spp. 6 inches Western mannagrass Glyceria occidentalis seed Velvetgrass Holcus mollis seed Slender rush Juncus tenuis 6 inches Watercress* Rorippa nasturtium-aquaticum 12 inches Water parsley* Oenanthe sarmentosa 6 inches Hardstem bulrush Scirpus acutus 6 inches Small-fruited bulrush Scirpus microcarpus 12 inches * Good choices for swales with significant periods of flow, such as those downstream of a detention facility. Cattail (Typha latifolia) is not appropriate for most wet swales because of its very dense and clumping growth habit which prevents water from filtering through the clump. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 82 Chapter 7 Figure V-7-22. Biofiltration Swale Access Features S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 83 Chapter 7 7.4.2 BMP T920 Wet Biofiltration Swale 7.4.2.1 Description A wet biofiltration swale is a variation of a basic biofiltration swale for use where the longitudinal slope is slight, water tables are high, or continuous low base flow is likely to result in saturated soil conditions. Where saturation exceeds about 2 weeks, typical grasses will die. Thus, vegetation specifically adapted to saturated soil conditions is needed. Different vegetation in turn requires modification of several of the design parameters for the basic biofiltration swale. 7.4.2.2 Performance Objectives To remove low concentrations of pollutants such as TSS, heavy metals, nutrients, and petroleum hydrocarbons. 7.4.2.3 Applications/Limitations Wet biofiltration swales are applied where a basic biofiltration swale is desired but not allowed or advisable because one or more of the following conditions exist: • The swale is located on glacial till soils and is downstream of a detention pond providing flow control. • Saturated soil conditions are likely because of seeps or base flows on the site. • Longitudinal slopes shall be less than 2 percent. 7.4.2.4 Criteria Use the same sizing and criteria as for basic biofiltration swales except for the following: 1. Adjust for extended wet season flow. • If the swale will be downstream of a detention pond or vault providing flow control, multiply the treatment area (bottom width times length) of the swale by 2, and readjust the swale length, if desired. Maintain a 5:1 length to width ratio. 2. Swale geometry. • The bottom width may be increased to 25 feet maximum, but a length-to-width ratio of 5:1 must be provided. No longitudinal dividing berm is needed. The minimum swale length is 100 feet. • If longitudinal slopes are greater than 2 percent, the wet swale must be stepped so that the slope within the stepped sections averages 2 percent. Steps may be made of retaining retaining walls, log check dams, or short riprap sections. No underdrain or lowflow drain is required. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 84 Chapter 7 3. High-flow bypass • A high-flow bypass (i.e., an off-line design) is required for flows greater than the offline water quality design flow that has been increased by 3.5. The bypass may be an open channel parallel to the wet biofiltration swale. 4. Water Depth and Base Flow • Design water depth shall be 4 inches for all wetland vegetation selections. • No underdrains or low-flow drains are required. 5. Flow Velocity, Energy Dissipation, and Flow Spreading • No flow spreader is required. 6. Access • Access is only required to the inflow and outflow of the swale. Access along the swale is not required. • Wheel strips may not be used for access. 7. Planting Requirements • A list of acceptable plants and recommended spacing is shown in Table V-7-14. • A wetland seed mix may be applied by hydroseeding, but if coverage is poor, planting of rootstock or nursery stock is required. Poor coverage is considered to be more than 30 percent bare area through the upper 2/3 of the swale after four weeks. 8. Maintenance Considerations • Mowing of wetland vegetation is not required. However, harvesting of very dense vegetation may be desirable in the fall after plant die-back to prevent the sloughing of excess organic material into receiving waters. Fall harvesting of Juncus species is not recommended. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 85 Chapter 7 7.4.3 BMP T930 Continuous Inflow Biofiltration Swale 7.4.3.1 Description: In situations where water enters a biofiltration swale continuously along the side slope rather than discretely at the head, a different design approach–the continuous inflow biofiltration swale–is needed. The basic swale design is modified by increasing swale length to achieve an equivalent average residence time. 7.4.3.2 Applications A continuous inflow biofiltration swale is to be used when inflows are not concentrated, such as locations along the shoulder of a road without curbs. This design may also be used where frequent, small point flows enter a swale, such as through curb inlet ports spaced at intervals along a road, or from a parking lot with frequent curb cuts. In general, no inlet port shall carry more than about 10 percent of the flow. A continuous inflow swale is not appropriate for a a situation in which significant lateral flows enter a swale at some point downstream from the head of the swale. In this situation, the swale width and length must be recalculated from the point of confluence to the discharge point in order to provide adequate treatment for the increased flows. 7.4.3.3 Design Criteria Same as specified for basic biofiltration swale except for the following: • The design flow for continuous inflow swales must include runoff from the pervious side slopes draining to the swale along the entire swale length. Therefore, they must be on-line facilities. • If only a single design flow is used, the flow rate at the outlet should be used. The goal is to achieve an average residence time through the swale of 9 minutes as calculated using the on-line water quality design flow rate multiplied by the ratio, K (see footnotes in Table V-7-9). Assuming an even distribution of inflow into the side of the swale double the hydraulic residence time to a minimum of 18 minutes. • Interior side slopes above the water quality design treatment elevation shall be planted in grass. A typical lawn seed mix or the biofiltration seed mixes are acceptable. Landscape plants or groundcovers other than grass may not be used anywhere between the runoff inflow elevation and the bottom of the swale. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 86 Chapter 7 7.4.4 BMP T940 Basic Filter Strip 7.4.4.1 Description A basic filter strip is flat with no side slopes (Figure V-7-23). Untreated stormwater is distributed as sheet flow across the inlet width of a biofilter strip. 7.4.4.2 Applications/Limitations The basic filter strip is typically used on-line and adjacent and parallel to a paved area such as parking lots, driveways, and roadways. Where a filter strip area is compost-amended to a minimum of 10% organic content in accordance with BMP L613; with hydroseeded grass maintained at 95% density and a 4-inch length by mowing and periodic re-seeding (possible landscaping with herbaceous shrubs), the filter strip serves as an Enhanced Treatment option. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 87 Chapter 7 Figure V-7-23. Typical Filter Strip S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 88 Chapter 7 7.4.4.3 Design Criteria for Filter strips: • Use the Design Criteria specified in Table V-7-9. • Filter strips shall only receive sheet flow. • Use curb cuts 12-inch wide and 1-inch above the filter strip inlet. 7.4.4.4 Sizing Procedure 1. Calculate the design flow depth using Manning’s equation as follows: KQ = (1.49A R0.67 s 0.5)/n Substituting for AR: KQ = (1.49Ty1.67 s0.5)/n Where: Ty = Arectangle, ft2 y = Rrectangle, design depth of flow, ft. (1 inch maximum) Q = peak Water Quality design flow rate based on WWHM or an approved continuous simulation model, ft3/sec K = A ratio of the peak 10-minute flow predicted by SBUH to the water quality design flow rate estimated using the WWHM. The value of K for off-line systems is 3.5 and for on-line systems is 2.0.1 n = Manning’s roughness coefficient s = Longitudinal slope of filter strip parallel to direction of flow T = Width of filter strip perpendicular to the direction of flow, ft. A = Filter strip inlet cross-sectional flow area (rectangular), ft2 R = hydraulic radius, ft. Rearranging for y: y = [KQn/1.49Ts0.5]0.6 y must not exceed 1 inch 2. Calculate the design flow velocity V, ft./sec., through the filter strip: V = KQ/Ty V must not exceed 0.5 ft./sec 3. Calculate required length, ft., of the filter strip at the minimum hydraulic residence time, t, of 9 minutes: L = tV = 540 V 1 As in swale design, an adjustment factor of K accounts for the differential between the Water Quality design flow rate calculated using WWHM and the SBUH design flow. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 89 Chapter 7 7.4.5 BMP T950 Narrow Area Filter Strip 7.4.5.1 Description: This section describes a filter strip design2 for impervious areas with flowpaths of 30 feet or less that can drain along their widest dimension to grassy areas. 7.4.5.2 Applications/Limitations: A narrow area filter strip could be used at roadways with limited right-of-way, or for narrow parking strips. If space is available to use the basic filter strip design, that design should be used in preference to the narrow filter strip. 7.4.5.3 Design Criteria: Design criteria for narrow area filter strips are the same as specified for basic filter strips. The sizing of a narrow area filter strip is based on the length of flowpath draining to the filter strip and the longitudinal slope of the filter strip itself (parallel to the flowpath). 1. Determine the length of the flowpath from the upstream to the downstream edge of the impervious area draining sheet flow to the strip. Normally this is the same as the width of the paved area, but if the site is sloped, the flow path may be longer than the width of the impervious area. 2. Calculate the longitudinal slope of the filter strip (along the direction of unconcentrated flow), averaged over the total width of the filter strip. • The minimum slope size is 2 percent. If the slope is less than 2 percent, use 2 percent for sizing purposes. • The maximum allowable filter strip slope is 20 percent. If the slope exceeds 20 percent, the filter strip must be stepped so that the treatment areas between drop sections do not have a longitudinal slope greater than 20 percent. Provide erosion protection at the base and flow spreaders for the drop sections. Vertical drops along the slope must not exceed 12 inches in height. If this is not possible, a different treatment facility must be selected. 3. Select the appropriate filter strip length for the flowpath length and filter strip longitudinal slope (Steps 1 and 2 above) from the graph in Figure V-7-24. Design the filter strip to provide this minimum length L along the entire stretch of pavement draining into it. 2 This narrow area filter strip design method is included here because technical limitations exist in the basic design method which results in filter strips that are proportionately longer as the contributing drainage becomes narrower (a result that is counter-intuitive). Research by several parties is underway to evaluate filter strip design parameters. This research may lead to more stringent design requirements that would supersede the design criteria presented here. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Biofiltration Treatment Facilities Volume V 6 90 Chapter 7 To use the graph, find the length of the flowpath on one of the curves (interpolate between curves as necessary). Move along the curve to the point where the design longitudinal slope of the filter strip (x-axis) is directly below. Read the filter strip length on the y-axis which corresponds to the intersection point. 0.0 5.0 10.0 15.0 20.00% 5% 10% 15% 20% Filter Strip Slope Filter Strip Length (feet) Note: minimum allowable filter strip length is 4 feet Flowpath = 30 feet 20 feet 10 feet Figure V-7-24. Filter Strip Lengths for Narrow Right-of-Way S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 91 Chapter 8 Chapter 8 Wetpool Facilities 8.1 Purpose This Chapter presents the methods, criteria, and details for analysis and design of wetponds, wetvaults, and stormwater wetlands. These facilities have as a common element, a permanent pool of water -the wetpool. Each of the wetpool facilities can be combined with detention storage in a combined facility. 8.2 Best Management Practices The following wetpool facility BMPs are discussed in this chapter: BMP T1010 – Wetponds -Basic and Large BMP T1020 – Wetvaults BMP T1030 – Stormwater Wetlands BMP T1040 – Combined Detention and Wetpool Facilities The specific BMPs that are selected should be based on the Treatment Facility Menus discussed in Chapter 2. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 92 Chapter 8 8.2.1 BMP T1010 Wetponds -Basic and Large 8.2.1.1 Description: A wetpond is a constructed stormwater pond that retains a permanent pool of water ("wetpool") at least during the wet season. The volume of the wetpool is related to the effectiveness of the pond in settling particulate pollutants. As an option, a shallow marsh area can be created within the permanent pool volume to provide additional treatment for nutrient removal. Flow control can be provided in the "live storage" area above the permanent pool. Figure V-8-25 and Figure V-8-26 illustrate a typical wetpond. 8.2.1.2 Design Criteria: For a basic wetpond, the wetpool volume provided shall be equal to or greater than the total volume of runoff from the water quality design storm, which is the 6-month, 24-hour storm event. Alternatively, the 91st percentile, 24-hour runoff volume predicted by WWHM can be used. A large wetpond requires a wetpool volume at least 1.5 times larger than the total volume of runoff from the 6-month, 24-hour storm event. For private wetponds, a minimum three-inch (3”) diameter power conduit shall be grounded to the edge of the pond for possible future installation of aerators. Aerators are required to be installed on public ponds. Power provided to public ponds shall be independently metered. Specific power and aeration requirements will be determined case by case during plan review and will be based upon the size and configuration of the wetpond. Design features that encourage plug flow and avoid dead zones are: • Dissipating energy at the inlet. • Providing a large length-to-width ratio. • Providing a broad surface for water exchange using a berm designed as a broadcrested weir to divide the wetpond into two cells rather than a constricted area such as a pipe. • Maximizing the flowpath between inlet and outlet, including the vertical path, also enhances treatment by increasing residence time. General wetpond design criteria and concepts are shown in Figure V-8-25 and Figure V-8-26. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 93 Chapter 8 Figure V-8-25. Wetpond (top view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 94 Chapter 8 Figure V-8-26. Wetpond (side view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 95 Chapter 8 8.2.1.3 Sizing Procedure Procedures for determining a wetpond's dimensions and volume are outlined below. 1. Identify required wetpool volume using the SCS (now known as NRCS) curve number equations. A basic wetpond requires a volume equal to or greater than the total volume of runoff from the 6-month, 24-hour storm event, or, alternatively, the 91st percentile, 24-hour runoff volume using WWHM. A large wetpond requires a volume at least 1.5 times the total volume of runoff from the 6-month, 24-hour storm event or 1.5 times the 91st percentile, 24-hour runoff volume using an approved continuous runoff model. P S P S Qd 0.8 [ 0.2 ]2 + − = for P 0.2S and Qd = 0 for P < 0.2S Where: Qd = runoff depth in inches over area P = precipitation depth in inches over area S = potential maximum detention, in inches over area, due to infiltration, storage, etc. The area’s potential maximum depth, S, is related to its curve number, CN: S = (1000 /CN) −10 2. Determine wetpool dimensions. Determine the wetpool dimensions satisfying the design criteria outlined below and illustrated in Figure V-8-25 and Figure V-8-26. A simple way to check the volume of each wetpool cell is to use the following equation: V = h( A + A ) 1 2 2 where: V = wetpool volume (ft3) h = wetpool average depth (ft) A1 = water quality design surface area of wetpool (sf) A2 = bottom area of wetpool (sf) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 96 Chapter 8 3. Design pond outlet pipe and determine primary overflow water surface. The pond outlet pipe shall be placed on a reverse grade from the pond's wetpool to the outlet structure. Use the following procedure to design the pond outlet pipe and determine the primary overflow water surface elevation: a. Use the nomographs in Figure V-8-27 and Figure V-8-28 to select a trial size for the pond outlet pipe sufficient to pass the on-line WQ design flow Qwq as determined using WWHM. b. Use Figure V-8-29 to determine the critical depth dc at the outflow end of the pipe for Qwq. c. Use Figure V-8-30 to determine the flow area Ac at critical depth. d. Calculate the flow velocity at critical depth using continuity equation (Vc = Qwq /Ac). e. Calculate the velocity head VH (VH =Vc2 /2g, where g is the gravitational constant, 32.2 feet per second). f. Determine the primary overflow water surface elevation by adding the velocity head and critical depth to the invert elevation at the outflow end of the pond outlet pipe (i.e., overflow water surface elevation = outflow invert + dc + VH). g. Adjust outlet pipe diameter as needed and repeat Steps (a) through (e). 4. Determine wetpond dimensions. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 97 Chapter 8 Figure V-8-27. Headwater Depth for Smooth Interior Pipe Culverts with Inlet Control DIAMETER OF CULVERT (D) IN INCHES ENTRANCE TYPE HWD SCALE (1) (2) (3) Square edge with Groove end with Groove end headwall headwall projectingEXAMPLE D = 42 inches (3.0 feet). Q = 120 cfsHW* *D in feet HW D (feet) (1) (2) (3) 2.5 2.1 2.2 8.8 7.4 7.7 EXAMPLE DISCHARGE (Q) IN CFS HEADWATER DEPTH IN DIAMETERS (HW/D) To use scale (2) or (3) projecthorizontally to scale (1), thenuse straight inclined line throughD and Q scales, or reverse as illustrated. 1.0 23456810 20 30 40 50 60 12 15 18 21 24 27 30 33 36 80 100 200 300 400 500 600 800 1,000 42 48 54 60 2,000 3,000 4,000 5,000 6,000 8,000 10,000 72 84 96 108 120 132 144 156 168 180 ENTRANCE TYPE SQUARE EDGE WITHHEADWALL GROOVE END WITH GROOVE END PROJECTING HEADWALL PLAN PLAN (1) (2) (3) .5 .5 .5 .6 .6 .6 .7 .7 .7 .8 .8 .8 .9 .9 .9 1.0 1.0 1.0 1.5 1.5 1.5 2. 2. 3. 3. 3. 4. 4. 4. 5. 2. (3) (2) (1) 5. 5. 6. 6. 6. New Design ManualFigure 4.3.1.B Headwater Depth for Smooth Interior Pipe Culverts with Inlet ControlRevised 12-2-97/Mdev 􀀀􀀀􀀀􀀀􀀀􀀀􀀀􀀀 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 98 Chapter 8 Figure V-8-28. Headwater Depth for Corrugated Pipe Culverts with Inlet Control STANDARD C.M. DIAMETER OF CULVERT (D) IN INCHES STRUCTURAL PLATE C.M. ENTRANCE TYPE HWD SCALE (1) (2) (3) Headwall Mitered to conformto slopeProjectingEXAMPLE D = 36 inches (3.0 feet). Q = 66 cfsHW* *D in feet HW D (feet) (1) (2) (3) 1.8 2.1 2.2 5.4 6.3 6.6 EXAMPLE DISCHARGE (Q) IN CFS HEADWATER DEPTH IN DIAMETERS (HW/D) To use scale (2) or (3) projecthorizontally to scale (1), thenuse straight inclined line throughD and Q scales, or reverse as illustrated 1.0 23456810 20 30 40 50 60 12 15 18 21 24 27 30 33 36 80 100 200 300 400 500 600 800 1,000 42 48 54 60 2,000 3,000 4,000 5,000 6,000 8,000 10,000 72 84 96 108 120 132 144 156 168 180 ENTRANCE TYPE HEADWALL PLAN MITERED TOCONFORMTO SLOPESECTION PROJECTINGSECTION (1) (2) (3) .5 .5 .5 .6 .6 .6 .7 .7 .7 .8 .8 .8 .9 .9 .9 1.0 1.0 1.0 1.5 1.5 1.5 2. 2. 3. 3. 3. 4. 4. 4. 5. 2. (3) (2) (1) 5. 5. 6. 6. 6. New Design ManualFigure 4.3.1.C Headwater Depth for Corrugated Pipe Culverts with Inlet ControlRevised 11-24-97/Mdev 􀀀􀀀 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 6 99 Chapter 8 Figure V-8-29. Critical Depth of Flow for Circular Culverts S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 00 Chapter 8 Figure V-8-30. Circular Channel Ratios S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 01 Chapter 8 8.2.1.4 Wetpool Geometry • Divide the wetpool into two cells separated by a baffle or berm. The first cell shall contain between 25 to 35 percent of the total wetpool volume. The baffle or berm volume shall not count as part of the total wetpool volume. • Provide sediment storage in the first cell. The sediment storage shall have a minimum depth of 1-foot. Install a fixed sediment depth monitor in the first cell to gauge sediment accumulation unless an alternative gauging method is proposed. • The minimum depth of the first cell shall be 4 feet, exclusive of sediment storage requirements. The depth of the first cell may be greater than the depth of the second cell. • The maximum depth of each cell shall not exceed 8 feet (exclusive of sediment storage in the first cell). Plant pool depths of 3 feet or shallower (second cell) with emergent wetland vegetation (see planting requirements). • Place inlets and outlets to maximize the flowpath through the facility. The ratio of flowpath length to width from the inlet to the outlet shall be at least 3:1. The flowpath length is defined as the distance from the inlet to the outlet, as measured at middepth. The width at mid-depth can be found as follows: width = (average top width + average bottom width)/2. • Wetponds with wetpool volumes less than or equal to 4,000 cubic feet may be single celled (i.e., no baffle or berm is required). However, it is especially important in this case that the flow path length be maximized. The ratio of flow path length to width shall be at least 4:1 in single celled wetponds, but should preferably be 5:1. • All inlets shall enter the first cell. For multiple inlets, the length-to-width ratio shall be based on the average flowpath length for all inlets. • Line the first cell in accordance with the liner requirements contained in Section 3.4. 8.2.1.5 Berms, Baffles, and Slopes • A berm or baffle shall extend across the the full width of the wetpool, and tie into the wetpond side slopes. If the berm embankments are greater than 4 feet in height, the berm must be constructed by excavating a key with dimensions equal to 50 percent of the embankment cross-sectional height and width. This requirement may be waived if recommended by a geotechnical engineer for specific site conditions. The geotechnical analysis shall address situations in which one of the two cells is empty while the other remains full of water. • The top of the berm may extend to the WQ design water surface or be 1-foot below the WQ design water surface. If at the WQ design water surface, berm side slopes shall be 3H:1V. Berm side slopes may be steeper (up to 2H:1V) if the berm is submerged 1-foot. • If good vegetation cover is not established on the berm, erosion control measures shall be used to prevent erosion of the berm back-slope when the pond is initially filled. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 02 Chapter 8 • The interior berm or baffle may be a retaining wall provided that the design is prepared and stamped by a licensed civil engineer. If a baffle or retaining wall is used, it shall be submerged one foot below the design water surface to discourage access by pedestrians. • Criteria for wetpond side slopes are included in Section 0. 8.2.1.6 Embankments Embankments that impound water must comply with the Washington State Dam Safety Regulations (Chapter 173-175 WAC). If the impoundment has a storage capacity (including both water and sediment storage volumes) greater than 10 acre-feet (435,600 cubic feet or 3.26 million gallons) above natural ground level, then dam safety design and review are required by the Department of Ecology. Contact Ecology for information about this regulation. 8.2.1.7 Inlet and Outlet See Figure V-8-25 and Figure V-8-26 for details on the following requirements: • Submerge the inlet to the wetpond with the inlet pipe invert a minimum of two feet from the pond bottom (not including sediment storage). The top of the inlet pipe shall be submerged at least 1-foot, if possible. • Provide an outlet structure. Either a Type 2 catch basin with a grated opening (“jail house window”) or a manhole with a cone grate (“birdcage”) may be used (see Volume III, Figure III-2-9 for an illustration). • The pond outlet pipe (as opposed to the manhole or type 2 catch basin outlet pipe) shall be back-sloped or have a down-turned elbow, and extend 1 foot below the WQ design water surface. • Size the pond outlet pipe, at a minimum, to pass the on-line WQ design flow. The highest invert of the outlet pipe sets the WQ design water surface elevation. • The overflow criteria for single-purpose (treatment only, not combined with flow control) wetponds are as follows: o The requirement for primary overflow is satisfied by either the grated inlet to the outlet structure or by a birdcage above the pond outlet structure. o The bottom of the grate opening in the outlet structure shall be set at or above the height needed to pass the WQ design flow through the pond outlet pipe. The grate invert elevation sets the overflow water surface elevation. o The grated opening and downstream conveyance shall be sized to pass the 100-year design flow. The capacity of the outlet system shall be sized to pass the peak flow for the conveyance requirements. • Provide an emergency spillway and design it according to the requirements for detention ponds (see Volume III, Section 2.3.1). • The City may require a bypass/shutoff valve to enable the pond to be taken offline for maintenance purposes. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 03 Chapter 8 • A gravity drain for maintenance is recommended if grade allows. o The drain invert shall be at least 6 inches below the top elevation of the dividing berm or baffle. Deeper drains are encouraged where feasible, but must be no deeper than 18 inches above the pond bottom. o The drain shall be at least 8 inches (minimum) diameter and shall be controlled by a valve. Use of a shear gate is allowed only at the inlet end of a pipe located within an approved structure. o Provide operational access to the valve to the finished ground surface. o The valve location shall be accessible and well marked with 1-foot of paving placed around the box. It must also be protected from damage and unauthorized operation. o A valve box is allowed to a maximum depth of 5 feet without an access manhole. If over 5 feet deep, an access manhole or vault is required. • All metal parts shall be corrosion-resistant. resistant. Do not use galvanized materials. 8.2.1.8 Access and Setbacks • All facilities shall be a minimum of 20 feet from any structure, property line, and any vegetative buffer required by the local government, and 100 feet from any septic tank/drainfield. • All facilities shall be a minimum of 50 feet from any slope greater than 20 percent. A geotechnical report must address the potential impact of a wetpond on a slope steeper than 20% or if closer than 50 feet. • Provide access and maintenance roads and designed them according to the requirements for detention ponds. Access and maintenance roads shall extend to both the wetpond inlet and outlet structures. An access ramp (7H minimum:1V) shall be provided to the bottom of the first cell unless all portions of the cell can be reached and sediment loaded from the top of the pond. • If the dividing berm is also used for access, it should be built to sustain loads of up to 80,000 pounds. 8.2.1.9 Planting Requirements Planting requirements for detention ponds also apply to wetponds. • Large wetponds intended for phosphorus control shall not be planted within the cells, as the plants will release phosphorus in the winter when they die off. • If the second cell of a basic wetpond is 3 feet deep or shallower, the bottom area shall be planted with emergent wetland vegetation. See Table V-8-15 for recommended emergent wetland plant species for wetponds. The recommendations in Table V-8-15 are for all of western Washington. Local knowledge should be used to tailor this information to Auburn as appropriate. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 04 Chapter 8 • Cattails (Typha latifolia) shall not be used because they tend to crowd out other species and will typically establish themselves anyway. • If the wetpond discharges to a phosphorus-sensitive lake or wetland, shrubs that form a dense cover should be planted on slopes above the WQ design water surface on at least three sides. Native vegetation species shall be used in all cases. 8.2.1.10 Recommended Design Features The following features should be incorporated into the wetpond design where site conditions allow: • The method of construction of soil/landscape systems can cause natural selection of specific plant species. Consult a soil restoration or wetland soil scientist for sitespecific recommendations. The soil formulation will impact the plant species that will flourish or suffer on the site, and the formulation should be such that it encourages desired species and discourages undesired species. • For wetpool depths in excess of 6 feet, it is recommended that some form of recirculation be provided in the summer, such as a fountain or aerator, to prevent stagnation and low dissolved oxygen conditions. • A flow length-to-width ratio greater than the 3:1 minimum is desirable. If the ratio is 4:1 or greater, then the dividing berm is not required, and the pond may consist of one cell rather than two. A one-cell pond must provide at least 6-inches of sediment storage depth. • A tear-drop shape, with the inlet at the narrow end, rather than a rectangular pond is preferred since it minimizes dead zones caused by corners. • A small amount of base flow is desirable to maintain circulation and reduce the potential for low oxygen conditions during late summer. • Evergreen or columnar deciduous trees along the west and south sides of ponds are recommended to reduce thermal heating, except that no trees or shrubs may be planted on berms meeting the criteria of dams regulated for safety. In addition to shade, trees and shrubs also discourage waterfowl use and the attendant phosphorus enrichment problems they cause. Trees should be set back so that the branches will not extend over the pond. • The number of inlets to the facility should be limited; ideally there should be only one inlet. The flowpath length should be maximized from inlet to outlet for all inlets to the facility. • The access and maintenance road could be extended along the full length of the wetpond and could double as play courts or picnic areas. Placing finely ground bark or other natural material over the road surface would render it more pedestrian friendly. • The following design features should be incorporated to enhance aesthetics where possible: S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 05 Chapter 8 o Provide pedestrian access to shallow pool areas enhanced with emergent wetland vegetation. This allows the pond to be more accessible without incurring safety risks. o Provide side slopes that are sufficiently gentle to avoid the need for fencing (3H:1V or flatter). o Create flat areas overlooking or adjoining the pond for picnic tables or seating that can be used by residents. Walking or jogging trails around the pond are easily integrated into site design. o Include fountains or integrated waterfall features for privately maintained facilities. o Provide visual enhancement with clusters of trees and shrubs. On most pond sites, it is important to amend the soil before planting since ponds are typically placed well below the native soil horizon in very poor soils. Make sure dam safety restrictions against planting do not apply. o Orient the pond length along the direction of prevailing summer winds (typically west or southwest) to enhance wind mixing. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 06 Chapter 8 Table V-8-15. Emergent Wetland Species Recommended for Wetponds Species Common Name Notes Maximum Depth INUNDATION TO 1-FOOT Agrostis exarata1 Spike bent grass Prairie to coast 2 feet Carex stipata Sawbeak sedge Wet ground Eleocharis palustris Spike rush Margins of ponds, wet meadows 2 feet Glyceria occidentalis Western mannagrass Marshes, pond margins 2 feet Juncus tenuis Slender rush Wet soils, wetland margins Oenanthe sarmentosa Water parsley Shallow water along stream and pond margins; needs saturated soils all summer Scirpus atrocinctus (formerly S. cyperinus) Woolgrass Tolerates shallow water; tall clumps Scirpus microcarpus Small-fruited bulrush Wet ground to 18 inches depth 18 inches Sagittaria latifolia Arrowhead Inundation 1 to 2 feet Agrostis exarata1 Spike bent grass Prairie to coast Alisma plantago-aquatica Water plantain Eleocharis palustris Spike rush Margins of ponds, wet meadows Glyceria occidentalis Western mannagrass Marshes, pond margins Juncus effuses Soft rush Wet meadows, pastures, wetland margins Scirpus microcarpus Small-fruited bulrush Wet ground to 18 inches depth 18 inches Sparganium emmersum Bur reed Shallow standing water, saturated soils Inundation 1 to 3 feet Carex obnupta Slough sedge Wet ground or standing water 1.5 to 3 feet Beckmania syzigachne1 Western sloughgrass Wet prairie to pond margins Scirpus acutus2 Hardstem bulrush Single tall stems, not clumping 3 feet Scirpus validus2 Softstem bulrush Inundation GREATER THAN 3 feet Nuphar polysepalum Spatterdock Deep water 3 to 7.5 feet Nymphaea odorata1 White waterlily Shallow to deep ponds 6 feet 1 Non-native species. Beckmania syzigachne is native to Oregon. Native species are preferred. 2 Scirpus tubers must be planted shallower for establishment, and protected from foraging waterfowl until established. Emerging aerial stems should project above water surface to allow oxygen transport to the roots. Primary sources: Municipality of Metropolitan Seattle, Water Pollution Control Aspects of Aquatic Plants, 1990. Hortus Northwest, Wetland Plants for Western Oregon, Issue 2, 1991. Hitchcock and Cronquist, Flora of the Pacific Northwest, 1973. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 07 Chapter 8 8.2.1.11 Construction Criteria: • Remove sediment that has accumulated in the pond after construction in the drainage area of the pond is complete (unless used for a liner -see below). • Sediment that has accumulated in the pond at the end of construction may be used as a liner in excessively drained soils if the sediment meets the criteria for low permeability or treatment liners in keeping with guidance given in Chapter 3. Sediment used for a soil liner must be graded to provide uniform coverage and must meet the thickness specifications in Chapter 3. The sediment must not reduce the design volume of the pond. The pond must be over-excavated initially to provide sufficient room for the sediments to serve as a liner. 8.2.1.12 Operation and Maintenance: • All private drainage systems serving multiple lots shall require a signed Stormwater Easement and Maintenance agreement with the City. The agreement shall designate the systems to be maintained and the parties responsible for maintenance. Contact the City to determine the applicability of this requirement to a project. A specific maintenance plan shall be formulated outlining the schedule and scope of maintenance operations. • The pond may be inspected by the City. The maintenance standards contained in Volume I, Appendix D are measures for determining if maintenance actions are required as identified through the annual inspection. • Trim site vegetation as necessary to keep the pond free of leaves and to maintain the aesthetic appearance of the site. Revegetate sloped areas that have become bare and regrade eroded areas prior to revegetation. • Remove sediment when the 1-foot sediment zone is full plus 6 inches. Dispose of sediments in accordance with current local health department requirements and the Minimum Functional Standards for Solid Waste Handling. See Volume IV, Appendix D Recommendations for Management of Street Waste for further guidance. • Any standing water removed during the maintenance operation must be properly disposed of. The preferred disposal option is discharge to a sanitary sewer at an approved location. Other disposal options include discharge back into the wetpool facility or the storm sewer system if certain conditions are met. See Volume IV, Appendix D for additional guidance. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 08 Chapter 8 8.2.2 BMP T1020 Wetvaults 8.2.2.1 Description: A wetvault is an underground structure similar in appearance to a detention vault, except that a wetvault has a permanent pool of water (wetpool) which dissipates energy and improves the settling of particulate pollutants (see the wetvault details in Figure V-8-31). Being underground, the wetvault lacks the biological pollutant removal mechanisms, such as algae uptake, present in surface wetponds. 8.2.2.2 Applications and Limitations: A wetvault may be used for commercial, industrial, or roadway projects if there are space limitations precluding the use of other treatment BMPs. The use of wetvaults for residential development is highly discouraged. Combined detention and wetpools are allowed; see BMP T1040. If oil control is required for a project, a wetvault may be combined with an API oil/water separator. 8.2.2.3 Design Criteria: Sizing Procedure The wetpool volume for the wetvault shall be equal to or greater than the total volume of runoff from the 6-month, 24-hour storm event. Alternatively, the 91st percentile, 24-hour runoff volume estimated by WWHM may be used. Typical design details and concepts for the wetvault are shown in Figure V-8-31. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 09 Chapter 8 Figure V-8-31. Wetvault S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 10 Chapter 8 8.2.2.4 Wetpool Geometry Same as specified for wetponds (see BMP T1010) except for the following two modifications: • The sediment storage in the first cell shall be an average of 1-foot. Because of the v-shaped bottom, the depth of sediment storage needed above the bottom of the side wall is roughly proportional to vault width according to the schedule below: Vault Width Sediment Depth (from bottom of side wall) 15’ 10” 20’ 9” 40’ 6” 60’ 4” • The second cell shall be a minimum of 3 feet deep since planting cannot be used to prevent re-suspension of sediment in shallow water as it can in open ponds. 8.2.2.5 Vault Structure • Separate the vault into two cells by a wall or a removable baffle. If a wall is used, provide a 5-foot by 10-foot removable maintenance access for both cells. If a removable baffle is used, the following criteria apply: o The baffle shall extend from a minimum of 1-foot above the WQ design water surface to a minimum of 1-foot below the invert elevation of the inlet pipe. o The lowest point of the baffle shall be a minimum of 2 feet from the bottom of the vault, and greater if feasible. • If the vault is less than 2,000 cubic feet (inside dimensions), or if the length-to-width ratio of the vault pool is 5:1 or greater, the baffle or wall may be omitted and the vault may be one-celled. • Do not divide the two cells of a wetvault into additional subcells by internal walls. If internal structural support is needed, it is preferred that post and pier construction be used to support the vault lid rather than walls. Any walls used within cells must be positioned so as to lengthen, rather than divide, the flowpath. • Slope the bottom of the first cell toward the access opening. Slope shall be between 0.5 percent (minimum) and 2 percent (maximum). The second cell may be level (longitudinally) sloped toward the outlet, with a high point between the first and second cells. Sloping the second cell towards the access opening for the first cell is also acceptable. Alternatively, access openings may be positioned a maximum of 10 feet from any location within the vault. • Slope the vault bottom laterally a minimum of 5 percent from each side towards the center, forming a broad "v" to facilitate sediment removal. Note: More than one "v" may be used to minimize vault depth. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 11 Chapter 8 The City may allow the vault bottom to be flat if removable panels are provided over the entire vault. Removable panels shall be at grade, have stainless steel lifting eyes, and weigh no more than 5 tons per panel. • The highest point of a vault bottom must be at least 6 inches below the outlet elevation to provide for sediment storage over the entire bottom. • Evaluate buoyancy of the vault with the results presented in design documentation. • Wetvaults may be constructed using arch culvert sections provided the top area at the WQ design water surface is, at a minimum, equal to that of a vault with vertical walls designed with an average depth of 6 feet. • Wetvaults shall conform to the "Materials" and "Structural Stability" criteria specified for detention vaults in Volume III, Section 2.3.3. • Where pipes enter and leave the vault below the WQ design water surface, they shall be sealed using water tight seals or couplers. • Galvanized materials shall not be used unless coated. 8.2.2.6 Inlet and Outlet • Submerge the inlet to the wetvault. The inlet pipe invert shall be a minimum of 3 feet from the vault bottom. Submerge the top of the inlet pipe at least 1-foot, if possible. • Unless designed as an off-line facility, the capacity of the outlet pipe and available head above the outlet pipe shall be designed to convey the 100-year design flow for developed site conditions without overtopping the vault. The available head above the outlet pipe must be a minimum of 6 inches. • The outlet pipe shall be back-sloped or have tee section, the lower arm of which shall extend 1 foot below the WQ design water surface to provide for trapping of oils and floatables in the vault. • Center the inlet and outlet pipes over the “V” portion of the vault. 8.2.2.7 Access Requirements Same as for detention vaults (see Volume III, Section 2.3.3), except for the following additional requirement for wetvaults: • • Provide a minimum of 50 square feet of grate over the second cell. For vaults in which the surface area of the second cell is greater than 1,250 square feet, grate 4 percent of the top. This requirement may be met by one grate or by many smaller grates distributed over the second cell area. Note: A grated access door can be used to meet this requirement. 8.2.2.8 Access Roads, Right of Way, and Setbacks Same as for detention vaults (see Volume III, Section 2.3.3). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 12 Chapter 8 8.2.2.9 Recommended Design Features The following design features should be incorporated into wetvaults where feasible, but they are not specifically required: • The floor of the second cell should slope toward the outlet for ease of cleaning. • The inlet and outlet should be at opposing corners of the vault to increase the flowpath. • A flow length-to-width ratio greater than 3:1 minimum is desirable. • Lockable grates instead of solid manhole covers are recommended to increase air contact with the wetpool. • The number of inlets to the wetvault should be limited, and the flowpath length should be maximized from inlet to outlet for all inlets to the vault. 8.2.2.10 Construction Criteria Remove sediment that has accumulated in the vault after construction in the drainage area is complete. 8.2.2.11 Operation and Maintenance • Vault maintenance procedures must meet OSHA confined space entry requirements, which include clearly marking entrances to confined space areas. • Facilities may be inspected by the City. The maintenance standards contained in Volume I, Appendix D are measures for determining if maintenance actions are required as identified through the inspection. • Remove sediment when the 1-foot sediment zone is full plus 6 inches. Test sediments for toxicants in compliance with current disposal requirements. Dispose of sediments in accordance with current local health department requirements and the Minimum Functional Standards for Solid Waste Handling. See Volume IV, Appendix D Recommendations for Management of Street Waste for additional guidance. • Dispose of any standing water removed during the maintenance operation. The preferred disposal option is discharge to a sanitary sewer at an approved location. Other disposal options include discharge back into the wetpool facility or the storm sewer system if certain conditions are met. See Volume IV, Appendix D for additional guidance . S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 13 Chapter 8 8.2.2.12 Modifications for Combining with a Baffle Oil/Water Separator If the project site is a high-use site and a wetvault is proposed, the vault may be combined with a baffle oil/water separator to meet the runoff treatment requirements with one facility rather than two. • The sizing procedures for the baffle oil/water separator (Chapter 9) shall be run as a check to ensure the vault is large enough. If the oil/water separator sizing procedures result in a larger vault size, increase the wetvault size to match. • An oil retaining baffle shall be provided in the second cell near the vault outlet. The baffle shall not contain a high-flow overflow, or else the retained oil will be washed out of the vault during large storms. • The vault shall have a minimum length-to-width ratio of 5:1. • The vault shall have a design water depth-to-width ratio of between 1:3 and 1:2. • The vault shall be watertight and shall be coated to protect from corrosion. • Separator vaults shall have a shutoff mechanism on the outlet pipe to prevent oil discharges during maintenance and to provide emergency shut-off capability in case of a spill. Also, provide a valve box and riser. • Wetvaults used as oil/water separators must be off-line and must bypass flows greater than the off-line WQ design flow multiplied by 3.5. This will minimize the entrainment and/or emulsification of previously captured oil during very high flow events. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 14 Chapter 8 8.2.3 BMP T1030 Stormwater Treatment Wetlands 8.2.3.1 Description Stormwater treatment wetlands are shallow man-made ponds that are designed to treat stormwater through the biological processes associated with emergent aquatic plants (see the stormwater wetland details in Figure V-8-32 and Figure V-8-33). Wetlands created to mitigate disturbance impacts, such as filling of wetlands, shall not be used as stormwater treatment facilities. 8.2.3.2 Applications and Limitations The most critical factor for a successful design is the provision of an adequate supply of water for most of the year. Since water depths are shallower than in wetponds, water loss by evaporation is an important concern. Stormwater wetlands are a good WQ facility choice in areas with high winter groundwater levels. 8.2.3.3 Design Criteria Stormwater wetlands use most of the same design criteria as wetponds (see above). above). However, instead of gravity settling being the dominant treatment process, pollutant removal mediated by aquatic vegetation and the microbiological community associated with that vegetation becomes the dominant treatment process. Thus when designing wetlands, water volume is not the dominant design criteria. Rather, factors which affect plant vigor and biomass are the primary concerns. 8.2.3.4 Sizing Procedure 1. The design volume is the total volume of runoff from the 6-month, 24-hour storm event or, alternatively, the 91st percentile, 24-hour runoff volume using WWHM. 2. Calculate the surface area of the stormwater wetland. The surface area of the wetland shall be the same as the top area of a wetpond sized for the same site conditions. Calculate the surface area of the stormwater wetland by using the volume from Step 1 and dividing by the average water depth (use 3 feet). 3. Determine the surface area of the first cell of the stormwater wetland. Use the volume determined from Criterion 2 under "Wetland Geometry", below, and the actual depth of the first cell. 4. Determine the surface area of the wetland cell. Subtract the surface area of the first cell (Step 3) from the total surface area (Step 2). 5. Determine water depth distribution in the second cell. Decide if the top of the dividing berm will be at the surface or submerged (designer's choice). Adjust the distribution of water depths in the second cell according to Step 8 in Section 8.2.3.5. This will result in a facility that holds less volume than that determined in Step 1 above. This is acceptable. 6. Choose plants. See Table V-8-15 for a list of plants recommended for wetpond water depth zones, or consult a wetland scientist. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 15 Chapter 8 8.2.3.5 Wetland Geometry 1. Stormwater wetlands shall consist of two cells, a presettling cell and a wetland cell. 2. The presettling cell shall contain approximately 33 percent of the wetpool volume calculated in Step 1 above. 3. The depth of the presettling cell shall be between 4 feet (minimum) and 8 feet (maximum), excluding sediment storage. 4. Provide one-foot of sediment storage in the presettling cell. 5. The wetland cell shall have an average water depth of about 1.5 feet (plus or minus 3 inches). 6. Shape the "berm" separating the two cells such that its downstream side gradually slopes to form the second shallow wetland cell (see the section view in Figure V-8-32). Alternatively, the second cell may be graded naturalistically from the top of the dividing berm (see Step 8 below). 7. The top of the berm shall be either at the WQ design water surface or submerged 1 foot below the WQ design water surface. Correspondingly, the side slopes of the berm must meet the following criteria: a. If the top of berm is at the WQ design water surface, the berm side slopes shall be no steeper than 3H:1V. b. If the top of berm is submerged 1-foot, the upstream side slope may be up to 2H:1V. 8. Grade the bottom of the wetland cell in one of two ways: a. Shallow evenly graded slope from the upstream to the downstream edge of the wetland cell (see Figure V-8-32). b. A "naturalistic" alternative, with the specified range of depths intermixed throughout the second cell (see Figure V-8-33). A distribution of depths shall be provided in the wetland cell depending on whether the dividing berm is at the water surface or submerged (see Table V-8-16). The maximum depth shall be 2.5 feet in either configuration. 8.2.3.6 Lining Requirements In infiltrative soils, line both cells of the stormwater wetland. To determine whether a low-permeability liner or a treatment liner is required, determine whether the following conditions will be met. If soil permeability will allow sufficient water retention, lining may be waived. 1. The second cell must retain water for at least 10 months of the year. 2. The first cell must retain at least three feet of water year-round. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 16 Chapter 8 3. Use a complete precipitation record when establishing these conditions. Take into account evapo-transpiration losses as well as infiltration losses. Many wetland plants can adapt to periods of summer drought, so a limited drought period is allowed in the second cell. This may allow a treatment liner rather than a low permeability liner to be used for the second cell. The first cell must retain water year-round in order for the presettling function to be effective. 4. If a low permeability liner is used, place a minimum of 18 inches of native soil amended with good topsoil or compost (one part compost mixed with 3 parts native soil) over the liner. For geomembrane liners, a soil depth of 3 feet is recommended to prevent damage to the liner during planting. Hydric soils are not required. The criteria for liners given in Chapter 3 must be observed. 8.2.3.7 Inlet and Outlet Same as for wetponds (see BMP T1010). 8.2.3.8 Access and Setbacks • Location of the stormwater wetland relative to site constraints (e.g., buildings, property lines, etc.) shall be the same as for detention ponds (see Volume III). See Chapter 3 for typical setback requirements for WQ facilities. • Provide access and maintenance roads and design them according to the requirements for detention ponds (see Volume III). Extend access and maintenance roads shall to both the wetland inlet and outlet structures. Provide an access ramp (7H minimum:1V) to the bottom of the first cell unless all portions of the cell can be reached and sediment loaded from the top of the wetland side slopes. • If the dividing berm is also used for access, it should be built to sustain loads of up to 80,000 pounds. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 17 Chapter 8 Figure V-8-32. Stormwater Wetland – Option 1 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 18 Chapter 8 Figure V-8-33. Stormwater Wetland – Option 2 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 19 Chapter 8 Table V-8-16. Distribution of Depths in Wetland Cell Dividing Berm at WQ Design Water Surface Dividing Berm Submerged 1-Foot Depth Range (feet) Percent Depth Range (feet) Percent 0.1 to 1 25 1 to 1.5 40 1 to 2 55 1.5 to 2 40 2 to 2.5 20 2 to 2.5 20 8.2.3.9 Planting Requirements Plant the wetland cell with emergent wetland plants following the recommendations given in Table V-8-15 or the recommendations of a wetland specialist. Cattails (Typha latifolia) are not allowed. 8.2.3.10 Construction Criteria • Construction and maintenance considerations are the same as for wetponds. • Construction of the naturalistic alternative (Option 2) can be accomplished by first excavating the entire area to the 1.5-foot average depth. Then soil subsequently excavated to form deeper areas can be deposited to raise other areas until the distribution of depths indicated in the design is achieved. 8.2.3.11 Operation and Maintenance • Inspect wetlands at least twice per year during the first three years during both growing and non-growing seasons to observe plant species presence, abundance, and condition; bottom contours and water depths relative to plans; and sediment, outlet, and buffer conditions. • Schedule maintenance around sensitive wildlife and vegetation seasons. • Plants may require watering, physical support, mulching, weed removal, or replanting during the first three years. • Remove nuisance plant species and replant desirable species. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 20 Chapter 8 8.2.4 BMP T1040 Combined Detention and Wetpool Facilities 8.2.4.1 Description: Combined detention and WQ wetpool facilities have the appearance of a detention facility but contain a permanent pool of water as well. The following design procedures, requirements, and recommendations cover differences in the design of the stand-alone WQ facility when combined with detention storage. The following combined facilities are addressed: • Detention/wetpond (basic and large) • Detention/wetvault • Detention/stormwater wetland. There are two sizes of the combined wetpond, a basic and a large, but only a basic size for the combined wetvault and combined stormwater wetland. The facility sizes (basic and large) are related to the pollutant removal goals. See Chapter 3 for more information about treatment performance goals. 8.2.4.2 Applications and Limitations: Combined detention and water quality facilities are efficient for sites that also have detention requirements. The water quality facility may often be placed beneath the detention facility without increasing the facility surface area. However, the fluctuating water surface of the live storage will create unique challenges for plant growth and for aesthetics alike. The live storage component of the facility shall be provided above the seasonal high water table. 8.2.4.3 Design Criteria: Typical design details and concepts for a combined detention and wetpond are shown in Figure V-8-34 and Figure V-8-35. The detention portion of the facility shall meet the design criteria and sizing procedures set forth in Volume III. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 21 Chapter 8 Figure V-8-34. Combined Detention and Wetpond (top view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 22 Chapter 8 Figure V-8-35. Combined Detention and Wetpond (side view) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 23 Chapter 8 8.2.4.4 Sizing The sizing for combined detention and wetponds are identical to those for wetponds and for detention facilities. The wetpool volume for a combined facility shall be equal to or greater than the total volume of runoff from the 6-month, 24-hour storm event or the 91st percentile 24-hour runoff volume estimated by WWHM. Follow the standard procedure specified in Volume III to size the detention portion of the pond. 8.2.4.5 Detention and Wetpool Geometry • Do not include the wetpool and sediment storage volumes in the required detention volume. • The "Wetpool Geometry" criteria for wetponds (see BMP T1010) shall apply with the following modifications/clarifications: o The permanent pool may be shallower to comprise most of the pond bottom, or deeper positioned to comprise a limited portion of the bottom. Note, having the first wetpool cell at the inlet allows for more efficient sediment management than if the cell is moved away from the inlet. Wetpond criteria governing water depth must still be met. See Figure V-8-36 for two possibilities for wetpool cell placement. o The minimum sediment storage depth in the first cell is 1-foot. The 6 inches of sediment storage required for a detention pond does not need to be added to this, but 6 inches of sediment storage must be added to the second cell to comply with the detention sediment storage requirement. 8.2.4.6 Berms, Baffles and Slopes Same as for wetponds (see BMP T1010) 8.2.4.7 Inlet and Outlet The Inlet and Outlet criteria for wetponds shall apply with the following modifications: • Provide a sump in the outlet structure of combined ponds. • Design the detention flow restrictor and its outlet pipe according to the requirements for detention ponds (see Volume III). 8.2.4.8 Access and Setbacks The same as for wetponds. 8.2.4.9 Planting Requirements The same as for wetponds. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 24 Chapter 8 8.3 Combined Detention and Wetvault The sizing procedure for combined detention and wetvaults is identical to those outlined for wetvaults and for detention facilities. The design criteria for detention vaults and wetvaults must both be met, except for the following modifications or clarifications: • The minimum sediment storage depth in the first cell shall average 1-foot. The 6 inches of sediment storage required for detention vaults do not need to be added to this, but 6 inches of sediment storage must be added to the second cell to comply with detention vault sediment storage requirements. • The oil retaining baffle shall extend a minimum of 2 feet below the WQ design water surface. • If a vault is used for detention as well as water quality control, the facility may not be modified to function as a baffle oil/water separator as allowed for wetvaults in BMP T1020. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 25 Chapter 8 Figure V-8-36. Alternative Configurations of Detention and Wetpool Areas S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Wetpool Facilities Volume V 7 26 Chapter 8 8.4 Combined Detention and Stormwater Wetland 8.4.1 Sizing Criteria The sizing procedure for combined detention and stormwater wetlands is identical to those outlined for stormwater wetlands and for detention facilities. Follow the procedure specified in BMP T1030 to determine the stormwater wetland size. Follow the standard procedure specified in Volume III to size the detention portion of the wetland. Water Level Fluctuation Restrictions: The difference between the WQ design water surface and the maximum water surface associated with the 2-year runoff shall not be greater than 3 feet. If this restriction cannot be met, the size of the stormwater wetland must be increased. The additional area may be placed in the first cell, second cell, or both. If placed in the second cell, the additional area need not be planted with wetland vegetation or counted in calculating the average depth. 8.44.2 Design Criteria The design criteria for detention ponds and stormwater wetlands must both be met, except for the following modifications or clarifications The Wetland Geometry criteria for stormwater wetlands (see BMP T1030) shall be modified as follows: • The minimum sediment storage depth in the first cell is 1-foot. The 6 inches of sediment storage required for detention ponds does not need to be added to this, nor does the 6 inches of sediment storage in the second cell of detention ponds need to be added. 8.4.3 Inlet and Outlet Criteria The Inlet and Outlet criteria for wetponds shall apply with the following modifications: • Provide a sump in the outlet structure of combined facilities. • Design the detention flow restrictor and its outlet pipe according to the requirements for detention ponds (see Volume III). 8.4.4 Planting Requirements The Planting Requirements for stormwater wetlands are modified to use the following plants which are better adapted to water level fluctuations: Scirpus acutus (hardstem bulrush) 2 -6' depth Scirpus microcarpus (small-fruited bulrush) 1 -2.5' depth Sparganium emersum (burreed) 1 -2' depth Sparganium eurycarpum (burreed) 1 -2' depth Veronica sp. (marsh speedwell) 0 -1' depth In addition, the shrub Spirea douglasii (Douglas spirea) may be used in combined facilities. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 27 Chapter 9 Chapter 9 Oil and Water Separators 9.1 Purpose Oil and water separators remove oil and other water-insoluble hydrocarbons and settleable solids from stormwater runoff. This chapter provides a discussion of their application and design criteria. Best Management Practices (BMPs) are described for baffle type and coalescing plate separators. 9.2 Description Oil and water separators are typically the American Petroleum Institute (API) (also called baffle type) (American Petroleum Institute, 1990) or the coalescing plate (CP) type using a gravity mechanism for separation. See Figure V-9-37 and Figure V-9-38. Oil and water separators typically consist of three bays; forebay, separator section, and the afterbay. The CP separators need considerably less space for separation of the floating oil due to the shorter travel distances between parallel plates. A spill control (SC) separator (Figure V-9-39) is a simple catch basin with a T-inlet for temporarily trapping small volumes of oil. The spill control separator is included here for comparison only and is not designed for, or to be used for, treatment purposes. 9.3 Applications/Limitations The following are potential applications of oil and water separators where free oil is expected to be present at treatable high concentrations and sediment will not overwhelm the separator. • Commercial and industrial areas including petroleum storage yards, vehicle maintenance facilities, manufacturing areas, airports, utility areas (water, electric, gas), and fueling stations. (King County Surface Water Management, 2005). • Facilities that would require oil control BMPs under the high-use site threshold described in Chapter 2 including parking lots at convenience stores, fast food restaurants, grocery stores, shopping malls, discount warehouse stores, banks, truck fleets, auto and truck dealerships, and delivery services. (King County Surface Water Management, 2005). For low concentrations of oil, other treatments may be more applicable. These include sand filters and emerging technologies. Without intense maintenance oil/water separators may not be sufficiently effective in achieving oil and TPH removal down to required levels. Pretreatment should be considered if the level of total suspended solids (TSS) in the inlet flow would cause clogging or otherwise impair the long-term efficiency of the separator. For inflows from small drainage areas (fueling stations, maintenance shops, etc.) a coalescing plate (CP) type separator is typically considered, due to space limitations. However, if plugging of the plates is likely, then a new design basis for the baffle type API separator may be considered on an experimental basis (see Section 9.6). S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 28 Chapter 9 Figure V-9-37. API (Baffle Type) Separator S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 29 Chapter 9 Figure V-9-38. Coalescing Plate Separator S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 30 Chapter 9 Source: 1992 Ecology Manual Figure V-9-39. Spill Control Separator (not for oil treatment) 9.4 Site Suitability Consider the following site characteristics: • Sufficient land area • Adequate TSS control or pretreatment capability • Compliance with environmental objectives • Adequate influent flow attenuation and/or bypass capability • Sufficient access for operation and maintenance (O&M) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 31 Chapter 9 9.5 Design Criteria 9.5.1 General Considerations The following are design criteria applicable to API and CP oil/water separators: • If practicable, determine oil/grease (or TPH) and TSS concentrations, lowest temperature, pH, empirical oil rise rates in the runoff, and the viscosity and specific gravity of the oil. Also determine whether the oil is emulsified or dissolved. (Washington State Department of Ecology, 2005) Do not use oil/water separators for the removal of dissolved or emulsified oils such as coolants, soluble lubricants, glycols, and alcohols. • Locate the separator off-line and bypass the incremental portion of flows that exceed the off-line 15-minute water quality design flow rate multiplied by 3.5. If it is necessary to locate the separator on-line, try to minimize the size of the area needing oil control, and use the on-line water quality design flow rate multiplied by 2.0. • Use only storm drain pipes or impervious conveyances for routing oil contaminated stormwater to the oil and water separator. • Specify appropriate performance tests after installation and shakedown, and/or certification by a professional engineer that the separator is functioning in accordance with design objectives. Expeditious corrective actions must be taken if it is determined that the separator is not achieving acceptable performance levels. • Add pretreatment for TSS that could clog the separator, or otherwise impair the longterm effectiveness of the separator. • All piping entering and leaving the separator must be six inches (6”) minimum diameter. • If a pump mechanism is required to convey the discharge from the site to the sanitary sewer system, the pump must be designed to discharge to a controlled gravity outlet flow into the City system. • Access points in the top of the vault must be provided to allow a minimum twelveinch (12”) diameter access for observation and maintenance to all chambers of the separator. • Access doors as applicable, should be galvanized spring-assisted diamond plate with a penta-head bolt-locking latch and recessed lift handle. • Doors must open a full one hundred and eighty degrees (180º). • Access to the separator shall be maintained free for inspection at all times. 9.5.2 Criteria for Separator Bays • Size the separator bay for the off-line 15-minute water quality design flow rate predicted by WWHM multiplied by 3.5. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 32 Chapter 9 • To collect floatables and settleable solids, design the surface area of the forebay at 20 ft² per 10,000 ft² of area draining to the separator. The length of the forebay shall be 1/3-1/2 of the length of the entire separator. Include roughing screens for the forebay or upstream of the separator to remove debris, if needed. Screen openings shall be about 3/4 inch. • Include a submerged inlet pipe with a down-turned elbow in the first bay at least two feet from the bottom. The outlet pipe shall be a Tee, sized to pass the design peak flow and placed at least 12 inches below the water surface. • Include a shutoff mechanism at the separator outlet pipe. • Use absorbents and/or skimmers in the afterbay as needed. 9.5.3 Criteria for Baffles • Oil retaining baffles (top baffles) shall be located at least 1/4 of the total separator length from the outlet and shall extend down at least 50% of the water depth and at least 1 foot from the separator bottom. • Baffle height to water depth ratios shall be 0.85 for top baffles and 0.15 for bottom baffles. 9.6 Oil and Water Separator BMPs Two BMPs are described in this section: • BMP T1110 for baffle type separators • BMP T1111 for coalescing plate separators S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 33 Chapter 9 9.6.1 BMP T1110 API (Baffle type) Separator Bay 9.6.1.1 Design Criteria The criteria for small drainages is based on Vh, Vt, residence time, width, depth, and length considerations. As a correction factor API's turbulence criteria is applied to increase the length. 9.6.1.2 Sizing Criteria • Determine the oil rise rate, Vt, in cm/sec, using Stokes’ Law, or empirical determination, or 0.033 ft./min. for 60μ (micron) oil droplet size. The application of Stokes’ Law to site-based oil droplet sizes and densities, or empirical rise rate determinations recognizes the need to consider actual site conditions. In those cases the design basis would not be the 60 micron droplet size and the 0.033 ft/min. rise rate. Stokes Law equation for rise rate, Vt (cm/sec): Vt = [(g)(`w – `o)(d²)] /[(18*aw)] Where: Vt = the rise rate of the oil droplet (cm/s or ft/sec) g = acceleration due to gravity (cm/cm/s² or ft/s²) `w = density of water at the design temperature (g/cm³ or lbm/ft³) `o = density of oil at the design temperature (g/cm³ or lbm/ft³) d = oil droplet diameter (cm or ft) aw = absolute viscosity of the water (g/cms or lbm/fts) Use: oil droplet diameter, D=60 microns (0.006 cm) `w =0.999 g/cm³ at 32° F `o: Select conservatively high oil density, For example, if diesel oil @`o =0.85 g/cm³ and motor oil @`o = 0.90 can be present then use `o =0.90 g/cm³ w = 0.017921 poise, gm/cm-sec. at Tw=32 °F Use the following separator dimension criteria: o Separator water depth, 3 d8 feet (to minimize turbulence) o Separator width, 6-20 feet o Depth/width (d/w) of 0.3-0.5 S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 34 Chapter 9 For Stormwater Inflow from Drainages under 2 Acres Ecology modified the API criteria for treating stormwater runoff from small drainage areas (fueling stations, commercial parking lots, etc.) by using the design hydraulic horizontal velocity, Vh, for the design Vh/Vt ratio rather than the API minimum of Vh/Vt = 15. The API criteria appear applicable for greater than two acres of impervious drainage area. Performance verification of this design basis must be obtained during at least one wet season using the test protocol referenced in Chapter 10 for new technologies. The following is the sizing procedure using modified API criteria: 1. Determine Vt and select depth and width of the separator section based on above criteria. 2. Calculate the minimum residence time (tm) of the separator at depth d: tm = d/Vt 3. Calculate the horizontal velocity of the bulk fluid, Vh, vertical cross-sectional area, Av, and actual design Vh/Vt. Vh = Q/dw = Q/Av (Vh maximum at < 2.0 ft/min.) Q = (k) . Use a value of 3.5 for K for the site location multiplied by the off-line 15 minute water quality design flow rate in ft³/min determined by WWHM, at minimum residence time, tm At Vh/Vt determine F, turbulence and short-circuiting factor API F factors range from 1.28-1.74 (see Appendix D). 4. Calculate the minimum length of the separator section, l(s), using: l(s) = FQtm/wd = F(Vh/Vt)d l(t) = l(f) + l(s) +l(a) l(t) = l(t)/3 + l(s) + l(t)/4 Where: l(t) = total length of 3 bays l(f) = length of forebay l(a) = length of afterbay 5. Calculate V = l(s)wd = FQtm, and Ah = wl(s) V = minimum hydraulic design volume Ah = minimum horizontal area of the separator For Stormwater Inflow from Drainages > 2 Acres: Use Vh = 15 Vt and d = (Q/2Vh)¹/² (with d/w = 0.5) and repeat above calculations 3-5. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 35 Chapter 9 9.6.2 BMP T1111 Coalescing Plate (CP) Separator Bay 9.6.2.1 Design Criteria Calculate the projected (horizontal) surface area of plates needed using the following equation: Ah = Q/Vt = [Q] /[(0.00386) * ((Sw -So)/(aw))] Where Ah = horizontal surface area of the plates (ft²) Vt = rise rate of the oil droplet (ft/min) Q = design flowrate (ft³/min) The design flowrate is the off-line 15-minute water quality design flowrate predicted by WWHM multiplied by 3.5. Sw = specific gravity of water at the design temperature So = specific gravity of oil at the design temperature aw = absolute viscosity of the water (poise) • Plate spacing shall be a minimum of 3/4 inches (perpendicular distance between plates). • Select a plate angle between 45° to 60° from the horizontal. • Locate plate pack at least 6 inches from the bottom of the separator for sediment storage. • Add 12 inches minimum head space from the top of the plate pack and the bottom of the vault cover. • Design inlet flow distribution and baffles in the separator bay to minimize turbulence, short-circuiting, and channeling of the inflow especially through and around the plate packs of the CP separator. The Reynolds Number through the separator bay shall be <500 (laminar flow). • Include forebay for floatables and afterbay for collection of effluent. • The sediment-retaining baffle must be upstream of the plate pack at a minimum height of 18 in. • Design plates for ease of removal, and cleaning with high-pressure rinse or equivalent. 9.6.2.2 Operation and Maintenance • Prepare, regularly update, and implement an O & M Manual for the oil/water separators. • Inspect oil/water separators monthly during the wet season of October 1-April 30 (WEF & ASCE, 1998) to ensure proper operation, and, during and immediately after a large storm event of 1 inch per 24 hours. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Oil and Water Separators Volume V 7 36 Chapter 9 • Clean oil/water separators regularly to keep accumulated oil from escaping during storms. They must be cleaned by October 15 to remove material that has accumulated during the dry season, after all spills, and after a significant storm. Coalescing plates may be cleaned in-situ or after removal from the separator. An eductor truck may be used for oil, sludge, and washwater removal. Replace wash water in the separator with clean water before returning it to service. • Remove the accumulated oil when the thickness reaches 1-inch. Also remove sludge deposits when the thickness reaches 6 inches. • Replace oil absorbent pads before their sorbed oil content reaches capacity. • Train designated employees on appropriate separator operation, inspection, record keeping, and maintenance procedures. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Emerging Technologies Volume V 7 37 Chapter 10 Chapter 10 Emerging Technologies 10.1 Background Traditional best management practices (BMPs) such as wetponds and filtration swales may not be appropriate in many situations due to size and space restraints or their inability to remove target pollutants. Because of this, the stormwater treatment industry emerged and new stormwater treatment devices are currently in development. Emerging technologies are those new stormwater treatment devices that are continually being added to the stormwater treatment marketplace. These devices include both permanent and construction site treatment technologies. Many of these devices have not undergone complete performance testing so their performance claims cannot be verified. 10.2 Emerging Technology and the City of Auburn Typically devices with general use level designation (GULD) will be accepted for private stormwater treatment. Devices with GULD status may be accepted in the right-of-way with preapproval. 10.3 Ecology Role in Evaluating Emerging Technologies To aid local governments in selecting new stormwater treatment technologies the Department of Ecology (Ecology) developed the Technology Assessment Protocol – Ecology (TAPE) and Chemical Technology Assessment Protocol Ecology (CTAPE) protocols. These protocols provide manufacturers with guidance on stormwater monitoring so they may verify their performance claims. As a part of this process Ecology: • Posts information on emerging technologies at the emerging technologies website: http://www.ecy.wa.gov/programs/wq/stormwater/newtech/index.html. • Participates in all Technical Review Committee (TRC) and Chemical Technical Review Committee (CTRC) activities which include reviewing manufacturer performance data and providing recommendations on use level designations. • Grants use level designations based on performance and other pertinent data submitted by the manufacturers and vendors. • Provides oversight and analysis of all submittals to ensure consistency with this manual. 10.4 Evaluation of Emerging Technologies Local governments should consider the following as they make decisions concerning the use of new stormwater treatment technologies in their jurisdiction: Remember the Goal: The goal of any stormwater management program or BMP is to treat and release stormwater in a manner that does not harm beneficial uses. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Emerging Technologies Volume V 7 38 Chapter 10 Exercise Reasonable Caution: Before allowing a new technology for an application, the local government should review evaluation information based on the TAPE or CTAPE. An emerging technology cannot be used for new or redevelopment unless this technology has a use level designation. Having a use level designation means that Ecology and the TRC or CTRC reviewed system performance data and believe the technology has the ability to provide the level of treatment claimed by the manufacturer. To achieve the goals of the Clean Water Act and the Endangered Species Act, local governments may find it necessary to retrofit stormwater pollutant control systems for many existing stormwater discharges. In retrofit situations, the use of any BMP that makes substantial progress toward these goals is a step forward and Ecology encourages this. To the extent practical, the performance of BMPs used in in retrofit situations should be evaluated using the TAPE or CTAPE protocols. 10.5 Assessing Levels of Development of Emerging Technologies Ecology developed use level designations to assess levels of development for emerging technologies. The use level designations are based upon the quantity, quality, and type of performance data. There are three use level designations: pilot use level designation, conditional use level designation, and general use level designation. Pilot Use Level Designation (PULD) For technologies that have limited performance data, the pilot use level designation allows limited use to enable field testing to be conducted. Pilot use level designations may be given based solely on laboratory performance data. Pilot use level designations apply for a specified time period only. During this time period, the proponent must complete all field testing and submit a technology evaluation report (TER) to Ecology and the TRC. Ecology will limit the number of installations to five during the pilot use level period. Local governments may allow PULD technologies to be installed if the manufacturer agrees to conduct additional field testing based on the TAPE at all sites to obtain a general use level designation. Local governments covered by a municipal stormwater NPDES permit must notify Ecology in writing when a PULD technology is proposed. The form can be found: http://www.ecy.wa.gov /programs/wq/stormwater/newtech/PULDNOI.pdf Conditional Use Level Designation (CULD) For emerging technologies that have considerable performance data that was not collected per the TAPE protocol, the CULD was established. Conditional use level designations may be given if field data has been collected by a protocol that is reasonably consistent but does not necessarily fully meet the TAPE protocol. The field data must meet the statistical goals set out in the TAPE guidelines Appendix D. Laboratory data may be used to supplement field data. Technologies that are granted a CULD will be allowed continued use for a specified time period, during which the field testing necessary to obtain a general use level designation (GULD) must be completed and a TER must be submitted to Ecology and the TRC. Ecology will limit the number of installations to ten during the CULD period. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Emerging Technologies Volume V 7 39 Chapter 10 General Use Level Designation (GULD) The GULD confers a general acceptance for the specified applications (land uses). Technologies with a GULD may be used anywhere in Washington, subject to Ecology conditions. 10.6 Examples of Emerging Technologies for Stormwater Treatment and Control Go to the Ecology Emerging Technologies website to obtain information on technologies that have obtained a use level designation: http://www.ecy.wa.gov/programs/w q/stormwater/newtech/index.html THIS PAGE INTENTIONALLY LEFT BLANK. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Basic Treatment Receiving Waters Volume V 7 41 Appendix A Appendix A Basic Treatment Receiving Waters All Salt Waterbodies Rivers Upstream Point for Exemption Baker Anderson Creek Bogachiel Bear Creek Cascade Marblemount Chehalis Bunker Creek Clearwater Town of Clearwater Columbia Canadian Border Cowlitz Skate Creek Elwha Lake Mills Green Howard Hanson Dam Hoh South Fork Hoh River Humptulips West and East Fork Confluence Kalama Italian Creek Lewis Swift Reservoir Muddy Clear Creek Nisqually Alder Lake Nooksack Glacier Creek South Fork Nooksack Hutchinson Creek North River Raymond Puyallup Carbon River Queets Clearwater River Quillayute Bogachiel River Quinault Lake Quinault Sauk Clear Creek Satsop Middle and East Fork Confluence Skagit Cascade River Skokomish Vance Creek Skykomish Beckler River Snohomish Snoqualmie River Snoqualmie Middle and North Fork Confluence Sol Duc Beaver Creek Stillaguamish North and South Fork Confluence North Fork Stillaguamish Boulder River South Fork Stillaguamish Canyon Creek Suiattle Darrington Tilton Bear Canyon Creek Toutle North and South Fork Confluence North Fork Toutle Green River Washougal Washougal White Greenwater River Wind Carson Wynoochee Wishkah River Road Bridge S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Basic Treatment Receiving Waters Volume V 7 42 Appendix A Lakes County Washington King Sammamish King Union King Whatcom Whatcom Silver Cowlitz S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Procedure for Conducting a Volume V Pilot Infiltration Test 7 43 Appendix B Appendix B Procedure for Conducting a Pilot Infiltration Test The Pilot Infiltration Test (PIT) consists of a relatively large-scale infiltration test to better approximate infiltration rates for design of stormwater infiltration facilities. The PIT reduces some of the scale errors associated with relatively small-scale double ring infiltrometer or “stove-pipe” infiltration tests. It is not a standard test but rather a practical field procedure recommended by Ecology’s Technical Advisory Committee. Infiltration Test 1. Excavate the test pit to the depth of the bottom of the proposed infiltration facility. Lay back the slopes sufficiently to avoid caving and erosion during the test. 2. The horizontal surface area of the bottom of the test pit should be approximately 100 square feet. For small drainages and where water availability is a problem smaller areas may be considered as determined by the site professional. 3. Accurately document the size and geometry of the test pit. 4. Install a vertical measuring rod (minimum 5-ft. long) marked in half-inch increments in the center of the pit bottom. 5. Use a rigid 6-inch diameter pipe with a splash plate on the bottom to convey water to the pit and reduce side-wall erosion or excessive disturbance of the pond bottom. Excessive erosion and bottom disturbance will result in clogging of the infiltration receptor and yield lower than actual infiltration rates. 6. Add water to the pit at a rate that will maintain a water level between 3 and 4 feet above the bottom of the pit. A rotometer can be used to measure the flow rate into the pit. A water level of 3 to 4 feet provides for easier measurement and flow stabilization control. However, the depth should not exceed the proposed maximum depth of water expected in the completed facility. 7. Every 15-30 min, record the cumulative volume and instantaneous flow rate in gallons per minute necessary to maintain the water level at the same point (between 3 and 4 feet) on the measuring rod. 8. Add water to the pit until one hour after the flow rate into the pit has stabilized (constant flow rate) while maintaining the same pond water level (usually 17 hours). 9. After the flow rate has stabilized, turn off the water and record the rate of infiltration in inches per hour from the measuring rod data, until the pit is empty. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Procedure for Conducting a Volume V Pilot Infiltration Test 7 44 Appendix B Data Analysis 1. Calculate and record the infiltration rate in inches per hour in 30 minutes or one-hour increments until one hour after the flow has stabilized. NOTE: Use statistical/trend analysis to obtain the hourly flow rate when the flow stabilizes. This would be the lowest hourly flow rate. 2. Apply appropriate correction factors for site heterogeneity, anticipated level of maintenance and treatment to determine the site-specific design infiltration rate (see Table V-B-17). Table V-B-17. Correction Factors to be Used with In-Situ Infiltration Measurements to Estimate Long-Term Design Infiltration Rates Issue Partial Correction Factor Site variability and number of locations tested CFv = 1.5 to 6 Degree of long-term maintenance to prevent siltation and bio-buildup CFm = 2 to 6 Degree of influent control to prevent siltation and bio-buildup CFi = 2 to 6 Example The area of the bottom of the test pit is 8.5-ft. by 11.5-ft. Water flow rate was measured and recorded at intervals ranging from 15 to 30 minutes throughout the test. Between 400 minutes and 1,000 minutes the flow rate stabilized between 10 and 12.5 gallons per minute or 600 to 750 gallons per hour, or an average of (9.8 + 12.3) /2 = 11.1 inches per hour. Applying a correction factor of 5.5 for gravelly sand, the design long-term infiltration rate becomes 2 inches per hour, anticipating adequate maintenance and pre-treatment. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Geotextile Specifications Volume V 7 45 Appendix C Appendix C Geotextile Specifications Table V-C-18. Geotextile Properties for Underground Drainage Survivability Properties (WSDOT 2008 Standard Specifications or most current version) Geotextile Property Requirements1 Low Survivability Moderate Survivability Geotextile Property Test Method Woven/Nonwoven Woven/Nonwoven Grab Tensile Strength, min. in machine and x-machine direction ASTM D4632 180 lbs/115 lbs min. 250 lbs/160 lbs min. Grab Failure Strain, in machine and xmachine direction ASTM D4632 <50%/>50% <50%/>50% Seam Breaking Strength (if seams are present) ASTM D4632 and 160 lbs/100 lbs min. 220 lbs/140 lbs min. Puncture Resistance ASTM D6241 370 lbs/220lbs min. 495 lbs/310 lbs min. Tear Strength, min. in machine and xmachine direction ASTM D4533 67 lbs/40 lbs min. 80 lbs/50 lbs min. Ultraviolet (UV) Radiation stability ASTM D4355 50% strength retained min., after 500 hrs. hrs. in a xenon arc device 50% strength retained min., after 500 hrs. in a xenon arc device 1 All geotextile properties are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in the table). Table V-C-19. Geotextile for Underground Drainage Filtration Properties (WSDOT 2008 Standard Specifications or most current version) Geotextile Property Requirements1 Geotextile Property Test Method Class A Class B Class C AOS2 ASTM D4751 0.43 mm max. (#40 sieve) 0.25 mm max. (#60 sieve) 0.18 mm max. (#80 sieve) Water Permittivity ASTM D4491 0.5 sec -1 min. 0.4 sec -1 min. 0.3 sec -1 min. 1 All geotextile properties are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in the table). 2 Apparent Opening Size (measure of diameter of the pores in the geotextile) S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Geotextile Specifications Volume V 7 46 Appendix C Table V-C-20. Geotextile Strength Properties for Impermeable Liner Protection Geotextile Property Test Method Geotextile Property Requirements1 Grab Tensile Strength, min. in machine and x-machine direction ASTM D4632 250 lbs min. Grab Failure Strain, in machine and x-machine direction ASTM D4632 >50% Seam Breaking Strength (if seams are present) ASTM D4632 and ASTM D4884 (adapted for grab test) 220 lbs min. Puncture Resistance ASTM D4833 125 lbs min. Tear Strength, min. in machine and x-machine direction ASTM D4533 90 lbs min. Ultraviolet (UV) Radiation ASTM D4355 50% strength stability retained min., after 500 hrs. in weatherometer 1 All geotextile properties are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in the table). Applications 1. For sand filter drain strip between the sand and the drain rock or gravel layers specify Geotextile Properties for Underground Drainage, moderate survivability, Class A, from Table V-C-18 and Table V-C-19 in the Geotextile Specifications. 2. For sand filter matting located immediately above the impermeable liner and below the drains, the function of the geotextile is to protect the impermeable liner by acting as a cushion. The specification provided in Table V-C-20 should be used to specify survivability properties for the liner protection application. Table V-C-19, Class C should be used for filtration properties. Only nonwoven geotextiles are appropriate for the liner protection application. 3. For an infiltration drain specify Geotextile for Underground Drainage, low survivability, Class C, from Table V-C-18 and Table V-C-19 in the Geotextile Specifications. 4. For a sand bed cover a geotextile fabric is placed exposed on top of the sand layer to trap debris brought in by the stormwater and to protect the sand, facilitating easy cleaning of the surface of the sand layer. layer. However, a geotextile is not the best product for this application. A polyethylene or polypropylene geonet would be better. The geonet material should have high UV resistance (90% or more strength retained after 500 hours in the weatherometer, ASTM D4355), and high permittivity (ASTM D4491, 0.8 sec. -1 or more) and percent open area (CWO-22125, 10% or more). Tensile strength should be on the order of 200 lbs grab (ASTM D4632) or more. Courtesy of Tony Allen, Geotechnical Engineer-WSDOT Reference for Tables 1 and 2: Section 9-33.2 “Geotextile Properties,” 1998 Standard Specifications for Road, Bridge, and Municipal Construction S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Turbulence & Short-Circuiting Factor Volume V 7 47 Appendix D Appendix D Turbulence and Short-Circuiting Factor VH/VT Turbulence Factor (FT) F = 1.2 (FT) 20 1.45 1.74 15 1.37 1.64 10 1.27 1.52 6 1.14 1.37 3 1.07 1.28 Figure V-D-40. Recommended Values of F for Various Values of vH/Vt THIS PAGE INTENTIONALLY LEFT BLANK. Volume VI i Table of Contents Volume VI – Low-Impact Development and On-Site Stormwater Management Table of Contents Purpose of this Volume ........................................................... ........................................................749 Content and Organization of this Volume .......................................................................................749 Chapter 1 General Requirements .....................................................................................750 1.1 Objectives ................................................................ ..............................................................750 1.2 Site Assessment ................................................................................................................. ...750 1.3 Site Planning and Layout.......................................................................................................750 1.4 Retain Native Vegetation............................. ..........................................................................751 1.5 Minimize Clearing and Grading Impacts ............................................................................... 751 Chapter 2 Low Impact Development Best Management Practices.................................752 2.1 Application .................................................................................... .........................................752 2.2 Best Management Practices..................................................................................................752 2.2.1 Dispersion and Soil Quality BMPs .................................................................................. 753 2.2.1.1 BMP L610 Downspout Dispersion ......................................... ...............................753 2.2.1.2 BMP L611 Concentrated Flow Dispersion ............................................................759 2.2.1.3 BMP L612 Sheet Flow Dispersion ........................................................................761 2.2.1.4 BMP L613 Post-Construction Soil Quality and Depth...........................................763 2.2.1.5 BMP L614 Full Dispersion.....................................................................................766 2.2.2 Site Design BMPs ............................................................... ............................................ 769 2.2.2.1 BMP L620 Preserving Natural Vegetation ............................................................769 2.2.2.2 BMP L621 Better Site Design ...............................................................................770 2.2.3 Low Impact Development BMPS ...................................................................... .............. 771 2.2.3.1 BMP L630 Bioretention Areas (Rain Gardens) .....................................................772 2.2.3.2 BMP L631 Vegetated Rooftops (Green Roofs)....................... ..............................779 2.2.3.3 BMP L632 Rainfall Reuse Systems ......................................................................780 2.2.3.4 BMP L633 Alternate Paving Surfaces...................................................................781 2.2.3.5 BMP L634 Minimal Excavation Foundations ........................................................786 2.2.3.6 BMP L635 Reverse Slope Sidewalks....................................................................787 THIS PAGE INTENTIONALLY LEFT BLANK. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Purpose Volume VI Content and Organization Introduction 749 Volume VI: Low Impact Development and On-Site Stormwater Management Purpose of this Volume This volume focuses on the concept of low impact development. Low impact development is a stormwater management strategy that emphasizes conservation and use of existing natural site features integrated with engineered, small-scale stormwater controls to more closely mimic predevelopment hydrologic conditions. On-site stormwater management techniques are a key component of low impact development. All sites required to meet Minimum Requirement #5 must use dispersion and soil quality BMPs described under on-site management below to the maximum extent practicable unless their use would cause flooding or erosion impacts. This section should be used in conjunction with “Low Impact Development: Technical Guidance Manual for Puget Sound”, which can be found on the Puget Sound Partnership Partnership website: www.psp.wa.gov/documents.html Content and Organization of this Volume Volume VI contains two chapters: • Chapter 1 provides an overview of the general requirements for low impact development. • Chapter 2 provides detailed information pertaining to Best Management Practices (BMPS) for low impact development. Volume VI S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements Volume VI 7 50 Chapter 1 Chapter 1 General Requirements 1.1 Objectives The goal of low impact development is to manage stormwater generated from new development and redevelopment on-site so there will be no negative impacts to adjacent or downstream properties and no degradation to ground or surface waters. The following are list of objectives for low impact design: • Minimize the impacts of increased stormwater runoff from new development and redevelopment by maintaining peak flow frequencies and durations of the site’s undisturbed hydrologic condition. • For residential projects, retain and/or restore 65% of the site’s native soils and vegetation. For commercial projects, retain and/or restore 25% of the site’s native soils and vegetation. • Retain and incorporate natural site features that promote infiltration of stormwater on the developed site. • Utilize LID BMPs and minimize the use of traditional technologies to manage stormwater quality and quantity. • Manage stormwater as close to the source as possible. 1.2 Site Assessment Before implementing LID practices it is necessary to perform a site assessment which includes an assessment of both on-site and off-site conditions and features. See Chapter 2 of the “Low Impact Development: Technical Guidance Manual for Puget Sound” for more information on steps for performing a site assessment. 1.3 Site Planning and Layout Sites should be configured to reduce impervious surfaces and utilize natural drainage features. Chapter 3 of the “Low Impact Development: Technical Guidance Manual for Puget Sound” contains information and techniques for site planning. City of Auburn codes must be adhered to. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 General Requirements Volume VI 7 51 Chapter 1 1.4 Retain Native Vegetation Retain native vegetation to the maximum extent practicable in order to: • Reduce total impervious surface coverage • Provide infiltration areas for overland flows generated in adjacent developed portions of the project • Maintain the natural hydrology of the site. See BMP L620 and Chapter 4 of “Low Impact Development: Technical Guidance Manual for Puget Sound” for techniques on retaining native vegetation. 1.5 Minimize Clearing and Grading Impacts • Conduct a soils analysis prior to clearing and grading to identify predevelopment soil types and infiltration capabilities. • Keep grading to a minimum by incorporating natural topography. • Always use appropriate erosion and sediment control techniques when clearing and grading. See Volume 2 of this manual for erosion and sediment control measures. • Utilize techniques from Chapter 5 of “Low Impact Development: Technical Guidance Manual for Puget Sound”. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 52 Chapter 2 Chapter 2 Low Impact Development Best Management Practices This Chapter presents the methods for analysis and design of on-site stormwater management Best Management Practices (BMPs). Design procedures and requirements for stormwater management BMPs meeting Minimum Requirement #7, Flow Control, are contained in Volume 3. 2.1 Application Most of the on-site BMPs serve to control runoff flow rate as well as to provide runoff treatment. Nonpollution generating surfaces, such as rooftops and patios, may also use the infiltration BMPs contained in Volume 3, which provide flow control only. Pollution generating surfaces, such as driveways, small parking lots, and landscaping, must use on-site BMPs to provide some water quality treatment. The design criteria components in this manual must be used in order to obtain runoff credits. Runoff credits are considered when determining project thresholds. 2.2 Best Management Practices The following Low Impact Development BMPs are discussed in this Chapter: 2.2.1 Dispersion and Soil Quality BMPs BMP L610 Downspout Dispersion BMP L611 Concentrated Flow Dispersion BMP L612 Sheet Flow Dispersion BMP L613 Post-Construction Soil Quality and Depth BMP L614 Full Dispersion 2.2.2 Site Design BMPs BMP L620 Preserving Natural Vegetation BMP L621 Better Site Design 2.2.3 Structural Low Impact Development BMPs BMP L630 Bioretention Areas (Rain gardens) BMP L631 Vegetated Rooftops BMP L632 Rainfall Reuse BMP L633 Alternate Paving Systems BMP L634 Minimal Excavation Foundations BMP L635 Reverse Slope Sidewalks Infiltration BMPs can be found in Volume 3 and Volume 5. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 53 Chapter 2 Projects shall employ these BMPs to infiltrate, disperse, and retain stormwater runoff on site to the maximum extent practicable without causing flooding or erosion impacts. Infiltration and dispersion systems require approval by the City. Sites that can fully infiltrate (see Volume 3, Chapter 3 and Volume 5, Chapter 5) or fully disperse (see BMP L614) are not required to provide runoff treatment or flow control facilities. Full dispersion credit is limited to sites with a maximum of 10% effective impervious area that is dispersed through 65% of the site maintained in natural vegetation. Impervious surfaces that are not fully dispersed should be partially dispersed to the maximum extent practicable and then hydrologically modeled. Minimum requirements still apply to those portions of a site that exceed thresholds described in Volume 1. 2.2.1 Dispersion and and Soil Quality BMPs 2.2.1.1 BMP L610 Downspout Dispersion Purpose and Definition Downspout dispersion BMPs are splashblocks or gravel-filled dispersion trenches that serve to spread roof runoff over vegetated pervious areas. Dispersion attenuates peak flows by slowing entry of the runoff into the conveyance system, allows for some infiltration, and provides some water quality benefits. Applications Downspout dispersion may be used on all sites that cannot infiltrate roof runoff and that meet the feasibility setback requirements. Flow Credit for Roof Downspout Dispersion If roof runoff is dispersed according to the requirements of this section, and the vegetative flowpath of the roof runoff is 50 feet or greater through undisturbed native landscape or lawn/landscape area that meets BMP L613, the roof area may be modeled as a grassed surface. General Design Criteria for Dispersion Trenches and Splashblocks Also see Additional Design Criteria sections. Maintain a vegetated flowpath of at least 50 feet in length between the outlet of the trench and the top of slopes steeper than 20% and greater than 10 feet high. A geotechnical analysis and report must be prepared addressing the potential impact of the facility on the slope. Vegetated flowpaths must be covered with well-established lawn or pasture, landscaping with well-established groundcover, or native vegetation with natural groundcover. The groundcover shall be dense enough to help disperse and infiltrate flows and to prevent erosion. For sites with multiple dispersion trenches or splashblocks, a minimum separation of 10 feet is required between flowpaths. The City may require a larger separation based upon site conditions such as slope, soil type, and total contributing area. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 54 Chapter 2 • Place all dispersions systems at least 10 feet from any structure. If necessary, setbacks shall be increased from the minimum 10 feet in order to maintain a 1:1 side slope for future excavation and maintenance. • Place all dispersion systems at least 5 feet from any property line. If necessary, setbacks shall be increased from the minimum 5 feet in order to maintain a 1:1 side slope for future excavation and maintenance. • Setback dispersion systems from sensitive areas, steep slopes, landslide hazard areas, and erosion hazard areas as governed by Auburn City Code. • No erosion or flooding of downstream properties shall result. • Runoff discharged towards landslide hazard areas must be evaluated by a geotechnical engineer or qualified geologist. Do not place the discharge point on or above slopes greater than 20% or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and City approval. • For sites with septic systems, place the discharge point downgradient of the drainfield primary and reserve areas. This requirement can be waived by the City's permit review staff if site topography will clearly prohibit flows from intersecting the drainfield. Additional Design Criteria for Dispersion Trenches • Design dispersion trenches as shown in Figure VI-2-1 and Figure VI-2-2. • Maintain a vegetated flowpath of at least 25 feet in length between the outlet of the trench and any property line, structure, stream, wetland, or impervious surface. Sensitive area buffers may count towards flowpath lengths • Maintain a vegetated flowpath of at least 50 feet in length between the outlet of the trench and any steep slope. • Trenches serving up to 700 square feet of roof area may be simple 10-foot-long by 2-foot-wide gravel filled trenches as shown in Figure VI-2-1. For roof areas larger than 700 square feet, a dispersion trench with notched grade board as shown in Figure VI-2-2 may be used as approved by the City. The total length of this design must provide at least 10 feet of trench per 700 square feet of roof area and not exceed 50 feet. Additional Design Criteria for Splashblocks In general, if the ground is sloped away from the building foundation, and there is adequate vegetation and area for effective dispersion, splashblocks will adequately disperse storm runoff. If the ground is fairly level, if the structure includes a basement, or if foundation drains are proposed, splashblocks with downspout extensions may be a better choice because the discharge point is moved away from the foundation. Downspout extensions can include piping to a splashblock/dischar ge point a considerable distance from the downspout, as long as the runoff can travel through a well-vegetated area as described below. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 55 Chapter 2 The following conditions must be met to use splashblocks: • Design splashblocks as shown in Figure VI-2-3. • Maintain a vegetated flowpath of at least 50 feet between the discharge point and any property line, structure, stream, wetland, lake, or other impervious surface. Sensitive area buffers may count toward flowpath lengths. • Do not direct flows onto sidewalks. • A maximum of 700 square feet of roof area may drain to each splashblock. • Place a splashblock or a pad of crushed rock (2 feet wide by 3 feet long by 6 inches deep) at each downspout discharge point. • No erosion or flooding of downstream properties may result. • Splashblocks may not be placed on or above slopes greater than 20% or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and approval by the City. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 56 Chapter 2 Figure VI-2-1. Typical Dispersion Trench S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 57 Chapter 2 Figure VI-2-2. Standard Dispersion Trench with Notched Grade Board S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 58 Chapter 2 Figure VI-2-3. Typical Downspout Splashblock Dispersion S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 59 Chapter 2 2.2.1.2 BMP L611 Concentrated Flow Dispersion Purpose and Definition Dispersion of concentrated flows from driveways or other pavement through a vegetated pervious area attenuates peak flows by slowing entry of the runoff into the conveyance system, allows for some infiltration, and provides some water quality benefits. Applications and Limitations • Any situation where concentrated flow can be dispersed through vegetation. • Dispersion for driveways will generally only be effective for single-family residences on large lots and in rural short plats. Lots proposed by short plats in urban areas will generally be too small to provide effective dispersion of driveway runoff. • Figure VI-2-4 shows two possible ways of spreading flows from steep driveways. Design Criteria • Maintain a vegetated flowpath of at least 50 feet between the discharge point and any property line, structure, steep slope, stream, lake, wetland, lake, or other impervious surface. • A maximum of 700 square feet of impervious area may drain to each concentrated flow dispersion BMP. • Place a pad of crushed rock (2 feet wide by 3 feet long by 6 inches deep) at each discharge point. • No erosion or flooding of downstream properties shall result. • Runoff discharged towards landslide hazard areas must be evaluated by a geotechnical engineer or qualified geologist. The discharge point shall not be placed on or above slopes greater than 20% or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and approval by the City. • For sites with septic systems, locate the discharge point downgradient of the drainfield primary and reserve areas. This requirement may be waived by the City if site topography clearly prohibits flows from intersecting the drainfield or where site conditions indicate that this is unnecessary (see Volume 3, Chapter 2). Flow Credits for Concentrated Flow Dispersion Where concentrated flow dispersion is used to disperse runoff into an undisturbed native landscape area or an area that meets the requirements of “Post-Construction Soil Quality and Depth”, and the vegetated flow path is at least 50 feet in length, the impervious area may be modeled as landscaped area. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 60 Chapter 2 Figure VI-2-4. Typical Concentrated Flow Dispersion for Steep Driveways S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 61 Chapter 2 2.2.1.3 BMP L612 Sheet Flow Dispersion Purpose and Definition Sheet flow dispersion is the simplest method of runoff control. This BMP can be used for any impervious or pervious surface that is graded so as to avoid concentrating flows. Because flows are already dispersed as they leave the surface, they need only traverse a narrow band of adjacent vegetation for effective attenuation and treatment. Applications and Limitations Flat or moderately sloping (<15% slope) impervious surfaces such as driveways, sport courts, patios, and roofs without gutters; sloping cleared areas that are comprised of bare soil, non-native landscaping, lawn, and/or pasture; or any situation where concentration of flows can be avoided. Design Criteria • See Figure VI-2-5 for details for driveways. • Provide a 2-foot-wide transition zone to discourage channeling between the edge of the driveway pavement and the downslope vegetation, or under building eaves. This may be an extension of subgrade material (crushed rock), modular pavement, drain rock, or other material acceptable to the City. • Provide a vegetated buffer width of 10 feet of vegetation for up to 20 feet of width of paved or impervious surface. Add an additional 5 feet of width for each additional 20 feet of width or fraction thereof. • Provide a vegetated buffer width of 25 feet of vegetation for up to 150 feet of contributing cleared area (i.e., bare soil, non-native landscaping, lawn, and/or pasture). Slopes within the 25-foot minimum flowpath through vegetation should be no steeper than 8 percent. If this criterion cannot be met due to site constraints, the 25-foot flowpath length must be increased 1.5 feet for each percent increase in slope above 8%. • No erosion or flooding of downstream properties may result. • Runoff discharge toward landslide hazard areas must be evaluated by a geotechnical engineer or a qualified qualified geologist. Do not place the discharge point on or above slopes greater than 20% or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and approval by the City. • For sites with septic systems, place the discharge point downgradient of the drainfield primary and reserve areas. This requirement may be waived by the City if site topography clearly prohibits flows from intersecting the drainfield or where site conditions indicate that this is unnecessary (see Volume 3, Chapter 2). Flow Credits for Sheet Flow Dispersion Where sheet flow dispersion is used to disperse runoff into an undisturbed native landscape area or an area that meets the requirements of “Post-Construction Soil Quality and Depth”, the impervious area may be modeled as landscaped area. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 62 Chapter 2 Figure VI-2-5. Sheet Flow Dispersion for Driveways S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 63 Chapter 2 2.2.1.4 BMP L613 Post-Construction Soil Quality and Depth Purpose and Definition Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant biofiltration; water interflow storage and transmission; and pollutant decomposition. These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod. Not only are these important stormwater functions lost, but such landscapes themselves become pollution generating pervious surfaces due to increased use of pesticides, fertilizers, and other landscaping and household/industrial chemicals, the concentration of pet wastes, and pollutants that accompany roadside litter. Applications and Limitations • Soil amendments are required for the disturbed areas of sites subject to Minimum Requirement #5. • Where Minimum Requirement #5 does not apply, and the site is proposing a traditional lawn installation, compost-amended lawn soil is strongly encouraged. • Use soil amendments in areas that will be incorporated into the stormwater drainage system such as vegetated channels, rain gardens, bioretention areas, and lawn and landscaped areas. Design Criteria Soil Retention • The duff layer and native topsoil should be retained in an undisturbed state to the maximum extent practicable. In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. Soil Quality • All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility or engineered as structural fill or slope shall, at project completion, demonstrate the following: o A topsoil layer with a minimum organic matter content of ten percent dry weight in planting beds, and 5% organic matter content in turf areas, and a pH from 6.0 to 8.0 or matching the pH of the original undisturbed soil. o The topsoil layer shall have a minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 64 Chapter 2 • Planting beds have been mulched with 2 inches of organic material • Quality of compost and other materials used to meet the organic content requirements: o The organic content for “pre-approved” amendment rates can be met only using compost that meets the definition of “composted materials” in WAC 173-350-220. The WAC is available online at: http://www.ecy.wa.gov/programs/swfa/facilities/350.html The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25:1. The carbon to nitrogen ratio may be as high as 35:1 for plantings composed entirely of plants native to the Puget Sound Lowlands region. o Calculated amendment rates may be met through use of composted materials as defined above; or other organic materials amended to meet the carbon to nitrogen ratio requirements, and meeting the contaminant standards of Grade A Compost. • The resulting soil is conducive to the type of vegetation to be established. Implementation Options: Use one of the following options to meet the post construction soil quality and depth requirements. Use the most recent version of “Guidelines for Resources for Implementing Soil Quality and Depth BMP T5.13” to meet the requirements of this BMP. This guidance can be found online at: www.soilsforsalmon.org • Leave native vegetation and soil undisturbed, and protect from compaction during construction. • Amend existing site topsoil or subsoil either at default “pre-approved” rates, or at custom calculated rates based on specifiers’ tests of the soil and amendment. • Stockpile existing topsoil during grading, and replace it prior to planting. Stockpiled topsoil must also be amended if needed to meet the organic matter or depth requirements, either at a default “pre-approved” rate or at a custom calculated rate. • Import topsoil mix of sufficient organic content and depth to meet the requirements. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 65 Chapter 2 Maintenance • Soil quality and depth should be established toward the end of construction and once established, should be protected from compaction, such as from large machinery use, and from erosion. • Soil should be planted and mulched after installation. • Plant debris or its equivalent should be left on the soil surface to replenish organic matter. • It should be possible to reduce use of irrigation, fertilizers, herbicides, and pesticides. These activities should be adjusted where possible, rather than continuing to implement formerly established practices. Flow Reduction Credits for BMP L613 Flow reduction credits can be taken in runoff modeling when Post-Construction Soil Quality and Depth is used as part of a dispersion design under the conditions described in: BMP L610 Downspout Dispersion BMP L611 Concentrated Flow Dispersion BMP L612 Sheet Flow Dispersion Volume 3, Appendix A S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 66 Chapter 2 2.2.1.5 BMP L614 Full Dispersion Purpose and Definition This BMP allows for "fully dispersing" runoff from impervious surfaces and cleared areas of development sites that preserve at least 65% of the site (or a threshold discharge area on the site) in a forest or native condition. Applications and Limitations • Full dispersion can be used as long as the developed areas draining to the native vegetation do not have impervious surfaces that exceed 10% of the entire site. • Other types of development that retain 65% of the site (or a threshold discharge area on the site) in a forested or native condition may also use these BMPs to avoid triggering the flow control facility requirement. • Runoff must be dispersed into native areas. Design Guidelines • Roof Downspouts -Roof surfaces that comply with the downspout infiltration requirements in Volume 3, Chapter 3, are considered to be "fully dispersed" (i.e., zero percent effective imperviousness). All other roof surfaces are considered to be "fully dispersed" (i.e., at or approaching zero percent effective imperviousness) only if they are within a threshold discharge area that is or will be more than 65% forested (or native vegetative cover) and less than 10% impervious (total), and if they comply with the downspout dispersion requirements of BMP L610, and have vegetated flow paths through native vegetation exceeding 100 feet. • Driveway Dispersion -Driveway surfaces are considered to be "fully dispersed" if they are within a threshold discharge area that is or will be more than 65% forested (or native vegetative cover) and less than 10% impervious (total), and if they comply with the driveway dispersion BMPs – BMP L611 and BMP L612 -and have flow paths through native vegetation exceeding 100 feet. This also holds true for any driveway surfaces that comply with the roadway dispersion BMPs described below. • Roadway Roadway Dispersion BMPs -Roadway surfaces are considered to be "fully dispersed" if they are within a threshold discharge area that is or will be more than 65% forested (or native vegetative cover) and less than 10% impervious (total), and if they comply with the following dispersion requirements: o Roadway runoff dispersion is allowed only on rural neighborhood collectors and local access streets. To the extent feasible, disperse driveways to the same standards as roadways to ensure adequate water quality protection of downstream resources. o Design the road section to minimize collection and concentration of roadway runoff. Use sheet flow over roadway fill slopes (i.e., where roadway subgrade is above adjacent right-of-way) wherever possible to avoid concentration. o When it is necessary to collect and concentrate runoff from the roadway and adjacent upstream areas (e.g., in a ditch on a cut slope), concentrated flows S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 67 Chapter 2 shall be incrementally discharged from the ditch via cross culverts or at the ends of cut sections. These incremental discharges of newly concentrated flows shall not exceed 0.5 cfs at any one discharge point from a ditch for the 100-year runoff event. Where flows at a particular ditch discharge point were already concentrated under existing site conditions (e.g., in a natural channel that crosses the roadway alignment), the 0.5-cfs limit would be in addition to the existing concentrated peak flows. o Ditch discharge points with up to 0.2 cfs discharge for the peak 100-year flow shall use rock pads or dispersion trenches to disperse flows. Ditch discharge points with between 0.2 and 0.5 cfs discharge for the 100-year peak flow shall use only dispersion trenches to disperse flows. o Dispersion trenches shall be designed to accept storm flows (free discharge) from a pipe, culvert, or ditch end, shall be aligned perpendicular to the flowpath, and shall be minimum 2 feet by 2 feet in section, 50 feet in length, filled with ¾-inch to 1½-inch washed rock, and provided with a level notched grade board (see Figure VI-2-2). Manifolds may be used to split flows up to 2 cfs discharge for the 100-year peak flow between up to 4 trenches. Dispersion trenches shall have a minimum spacing of 50 feet. o After being dispersed with rock pads or trenches, flows from ditch discharge points must traverse a minimum of 100 feet of undisturbed native vegetation before leaving the project site, or entering an existing onsite channel carrying existing concentrated flows across the road alignment. o Flowpaths from adjacent discharge points must not intersect within the 100-foot flowpath lengths, and dispersed flow from a discharge point must not be intercepted by another discharge point. To enhance the flow control and water quality effects of dispersion, the flowpath shall not exceed 15% slope, and shall be located within designated open space. o Ditch discharge points shall be located a minimum of 100 feet upgradient of steep slopes (i.e., slopes steeper than 40%), wetlands, and streams. o Where the City determines there is a potential for significant adverse impacts downstream (e.g., erosive steep slopes or existing downstream drainage problems), dispersion of roadway runoff may not be allowed, or other measures may be required. See Volume 1, Chapter 2 for geographic specific requirements. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 68 Chapter 2 Cleared Area Dispersion BMPs The runoff from cleared areas that are comprised of bare soil, non-native landscaping, lawn, and/or pasture is considered to be "fully dispersed" if it is dispersed through at least 25 feet of native vegetation in accordance with the following criteria: • The contributing flowpath of cleared area being dispersed must be no more than 150 feet. • Slopes within the 25-foot minimum flowpath through native vegetation should be no steeper than 8%. If this criterion cannot be met due to site constraints, the 25-foot flowpath length must be increased 1.5 feet for each percent increase in slope above 8%. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 69 Chapter 2 2.2.2 Site Design BMPs 2.2.2.1 BMP L620 Preserving Natural Vegetation Purpose Preserving natural vegetation on-site to the maximum extent practicable will minimize the impacts of development on stormwater runoff. Applications and Limitations On lots that are one acre or greater, preservation of 65 percent or more of the site in natural vegetation will allow the use of full dispersion techniques presented in BMP L614. Sites that can fully disperse are not required to provide runoff treatment or flow control facilities. Design Criteria • Situate the preserved area to maximize the preservation of wetlands, and to buffer stream corridors. • Place the preserved area in a separate tract or protect through recorded easements for individual lots. • If feasible, locate the preserved area downslope from the building sites, since flow control and water quality are enhanced by flow dispersion through duff, undisturbed soils, and native vegetation. • Show the preserved area on all property maps and clearly mark the area during clearing and construction on the site. Maintenance • Do not remove vegetation and trees from undisturbed areas, except for approved timber harvest activities and the removal of dangerous and diseased trees. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 70 Chapter 2 2.2.2.2 BMP L621 Better Site Design Purpose Fundamental hydrological concepts and stormwater management concepts can be applied at the site design phase that are: • More integrated with natural topography, • Reinforce the hydrologic cycle, • More aesthetically pleasing, and • Often less expensive to build. Design Criteria Define Development Envelope and Protected Areas – The first step in site planning is to define the development envelope. This is done by identifying protected areas, setbacks, easements and other site features, and by consulting applicable local standards and requirements. Site features to be protected may include important existing trees, steep slopes, erosive soils, riparian areas, or wetlands. By keeping the development envelope compact, environmental impacts can be minimized, construction costs can be reduced, and many of the site’s most attractive landscape features can be retained. In some cases, economics or other factors may not allow avoidance of all sensitive areas. In these cases, care can be taken to mitigate the impacts of development through site work and other landscape treatments. Minimize Directly Connected Impervious Areas Impervious areas directly connected to the storm drain system are the greatest contributors to urban nonpoint source pollution. Minimize these directly connected impervious areas. This can be done by limiting overall impervious land coverage or by infiltrating and/or dispersing runoff from these impervious areas. • Maximize Permeability -Within the development envelope, many opportunities are available to maximize the permeability of new construction. These include minimizing impervious areas, paving with permeable materials, clustering buildings, and reducing the land coverage of buildings by smaller footprints. All of these strategies make more land available for infiltration and dispersion through natural vegetation. • Build Narrower Streets -More than any other single element, street design has a powerful impact on stormwater quantity and quality. In residential development, streets and other transportation-related structures typically can comprise between 60 and 70 percent of the total impervious area, and, unlike rooftops, streets are almost always directly connected to the stormwater conveyance system. • Maximize Choices for Mobility -Given the costs of automobile use, both in land area consumed and pollutants generated, maximizing choices for mobility is a basic principle for environmentally responsible site design. By designing residential S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 71 Chapter 2 developments to promote alternatives to automobile use, a primary source of stormwater pollution can be mitigated. • Use Drainage as a Design Element -Unlike conveyance storm drain systems that hide water beneath the surface and work independently of surface topography, a drainage system for stormwater infiltration or dispersion can work with natural land forms and land uses to become a major design element of a site plan. 2.2.3 Low Impact Development BMPS Low impact development BMPs are structural BMPs that can be used to manage stormwater on-site. Using LID techniques can reduce surface runoff. For each category, basic design criteria is included. The design criteria components in this manual must be used in order to obtain runoff credits. Runoff credits are considered when determining project thresholds. The guidance provided in “Low Impact Development: Development: Technical Guidance Manual for Puget Sound”, found on the Puget Sound Partnership website: www.psp.wa.gov, should also be used in design. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 72 Chapter 2 2.2.3.1 BMP L630 Bioretention Areas (Rain Gardens) Purpose and Definition Bioretention areas are shallow stormwater retention systems designed to mimic forested systems by controlling stormwater through detention, infiltration, and evapotranspiration. Bioretention areas provide water quality treatment through sedimentation, filtration, adsorption, and phytoremediation. Bioretention facilities are integrated into the landscape to mimic natural hydrologic conditions better. Bioretention facilities may be used as a water quality facility or a water quality and flow control (retention) facility. Applicability and Limitations • Rain gardens can be used as on-lot retention facilities. • Rain gardens may be used to receive roof runoff in areas where traditional infiltration is not feasible. • Three feet of clearance is necessary between the lowest elevation of the bioretention soil or any underlying gravel layer and the seasonal high groundwater elevation or other impermeable layer if the area tributary to the facility meets or exceeds any of the following: o 5000 square feet of pollution-generating impervious surface o 10,000 square feet of impervious area o ¾ acre of lawn and landscape • For bioretention systems with a contributing area less than the above thresholds, a minimum of 1 foot of clearance is required from the seasonal high groundwater or other impermeable layer. • Bioretention facilities can be used in parking lots and any other type of development. • Bioretention systems may meet the requirements for basic and enhanced treatment when soil is designed in accordance with the requirements below and at least 91% of the influent runoff volume using WWHM is infiltrated. Drawdown requirements must also be met. Setback and Site Constraints • Assure that water movement through the surface soils and interflow will remain unobstructed and soils will remain uncompacted. • Locate bioretention facilities at least 10 feet from any structure or property line unless approved in writing by the City. • Locate bioretention facilities at least 50 feet back from slopes with a grade of 20% or greater. A geotechnical analysis must be prepared addressing the potential impact of the facility on the slope if closer than 50 feet or greater than 20%. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 73 Chapter 2 Design Criteria Flow Entrance/Presetting • Flow velocity entering the facility should be less than 1 ft/sec. • Use one of the four types of flow entrances: o Dispersed, low velocity flow across a grade or landscape area. o Dispersed flow across pavement or gravel and past wheel stops for parking areas. o Dispersed curb cuts for driveway or parking lot areas. Include rock or other erosion protection material in the channel entrance to dissipate energy. o Pipe flow entrance. Include rock or other erosion protection material at the facility entrance to dissipate energy and/or provide flow dispersion. • Do not place woody plants directly in the entrance flow path as they can restrict or concentrate flows. • A minimum 1-inch grade change between the edge of a contributing impervious surface and the vegetated flow entrance is required. • Install flow diversion and erosion control measures to protect the bioretention area from sedimentation until the upstream area is stabilized. • If the catchment area exceeds 2,000 square feet, a presettling facility may be required. Cell Ponding Area • The ponding area provides for surface storage and particulate settling, • Ponding depth and drawdown rate provide variable conditions that allow for a range of appropriate plant species. Soil must be allowed to dry out periodically in order to: o Restore hydraulic capacity of system. o Maintain infiltration rates. o Maintain adequate soil oxygen levels for healthy soil biota and vegetation. o Provide proper soil conditions for biodegradation and retention of pollutants. o Prevent conditions supportive of mosquito breeding. • The ponding depth shall be a maximum of 12 inches. • The surface pool drawdown time shall be 24 hours. • The minimum freeboard measured from the invert of the overflow pipe or earthen channel to facility overtopping elevation shall be 2” for drainage areas less than 1,000 square feet and 6” for drainage areas 1,000 square feet or greater. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 74 Chapter 2 • If berming is used to achieve the minimum top elevation, maximum slope on berm shall be 4H:1V, and minimum top width of design berm shall be 1 foot. Soil for berming shall be imported bioretention soil or amended native soil compacted to a minimum of 90% dry density. Overflow • Unless designed for full infiltration of the entire runoff volume, bioretention systems must include an overflow. • A drain pipe installed at the designed maximum ponding elevation and connected to a downstream BMP or an approved discharge point can be used as the overflow. • Overflow shall be designed to convey the 100-year recurrence interval flow. Soils • For bioretention systems to meet the requirements for basic and enhanced treatment the following requirements must be met: • The bioretention soil mix (BSM) shall meet the following requirements: o Have an infiltration rate between 1 and 2.4 inches per hour. o The CEC must be at least 5 meq/100 grams of dry soil. o The soil mix should be about 40% by volume compost and about 60% by volume aggregate component. The aggregate component shall meet the specifications in Table VI-2-1 o The compost component shall be stable, mature, and derived from organic waste materials including yard debris, wood wastes, or other organic matter. Compost must meet the Washington State compost regulations in WAC 173-350, which is available at http://www.ecy.wa.gov/programs/compost Table VI-2-1. Bioretention Soil Mix Aggregate Component Sieve Size Percent Passing 3/8” 100 #4 95-100 #10 75-90 #40 25-40 #100 4-10 #200 2-5 o Minimum depth of treatment soil must be 18 inches. o Soil depths of 24” and greater should be considered to provide improved removal of nutrients as needed, including phosphorus. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 75 Chapter 2 • For facilities that infiltrate and do not have an underdrain, a soils report, prepared by a soils professional, shall be required and must address the following for each bioretention area: o A minimum of one soil log or test pit is required at each facility. o The soil log shall extend a minimum of 4 feet below the bottom of the subgrade (the lowest point of excavation). o The soil log must describe the USDA textural class of the soil horizon through the depth of the log and note any evidence of high groundwater level, such as mottling. o Use infiltration rates of the native soil when sizing and modeling bioretention systems. Underdrain Only install underdrains in bioretention areas if: • Infiltration is not permitted and/or a liner is used, or • Where infiltration rates are not adequate to meet the maximum pool drawdown time. • Where the facility is not not utilized for infiltration. Underdrain pipe diameter will depend on hydraulic capacity required, 6-inch minimum. Use a geotextile fabric between the soil layer and underdrain. Planting • Plants must be tolerant of summer drought, ponding fluctuations, and saturated soil conditions. • Consider rooting depth when choosing plants. Roots must not damage underground infrastructure. • Locate slotted and perforated pipe at least 5 feet from tree roots and side sewer pipes. • Consider adjacent plant communities and potential invasive species. • Consider aesthetics, rain gardens should blend into surrounding landscapes. • The “Low Impact Development: Technical Guidance Manual for Puget Sound” Appendix 3 contains information for selecting proper bioretention vegetation. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 76 Chapter 2 Mulch Layer • Bioretention areas should be designed with a mulch layer. Properly selected mulch material reduces weed establishment, regulates soil temperatures and moisture, and adds organic matter to soil. Mulch should be: o Compost in the bottom of the facilities, o Wood chip mulch composed of shredded or chipped hardwood or softwood on cell slopes, o Free of weed seeds, soil, roots, and other material that is not trunk or branch wood and bark, o A maximum of 3 inches thick for compost or 4 inches thick for wood chips. • Mulch shall not include grass clippings, mineral aggregate or pure bark. • A dense groundcover can be used as an alternative to mulch though mulch most be used until the dense groundcover is established. Modeling and Sizing For sites with contributing area less than 2,000 square feet: Table VI-2-2 provides the square footage of the bottom of the rain garden per 1000 square feet of roof area. The same method of sizing can be used for rain gardens receiving driveway runoff if the soils meet the water quality treatment requirements outlined in Section 2.2.3.1 in the Soils subsection, or the runoff passes through a basic treatment facility before reaching the rain garden. Collection areas greater than 2000 square feet must be designed by a professional engineer. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 77 Chapter 2 Table VI-2-2. Sizing Table for Rain Gardens Soil Type Raingarden bottom (square feet) Coarse sands and cobbles 25 Medium sands 60 Fine sands, loamy sands 130 Sandy loam 160 Loam 225 For sites with contributing areas 2,000 square feet or more: Use WWHM and model the facility as an infiltration facility with appropriate stage-storage and overflow/outflow rates. Bioretention cells may be modeled as a layer of soil with infiltration to underlying soil, ponding, and overflow. The tributary area, cell bottom area, and ponding depth should be iteratively sized until the duration curves and/or peak volumes meet the flow control requirements. NOTE: WWHM Pro has the ability to model bioretention areas with or without underdrains so facility will be sized differently than described above. Contact the Washington State Department of Ecology for more information. Use the assumptions in Table VI-2-3 when sizing the facilities. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 78 Chapter 2 Table VI-2-3. Modeling Assumptions for Rain Garden Sizing Variable Assumption Computational Time Step 15 minutes Inflows to Facility Surface flow and interflow from drainage area routed to facility Precipitation and Evaporation Applied to Facility Yes Bioretention Soil Infiltration Rate For imported soils, for sites that have a contributing area of less than 5,000 square feet of pollution generating surfaces, less than 10,000 square feet of impervious area, and less than ¾ acre of landscaped area, reduce the infiltration rate of the BSM by a factor of 2. For sites above these thresholds, a reductions factor of 4 shall be applied. For compost amended native soil, rate is equal to native soil design infiltration rate. Bioretention Soil Porosity 40% Bioretention Soil Depth Minimum of 18 inches. Native Soil Infiltration Rate Measured infiltration rate with applicable safety factors. See Volume III for more information on infiltration rate determination. Infiltration Across Wetted Surface Area Only if sides slopes are 3:1 or flatter Overflow Overflow elevation set at maximum ponding elevation (excluding freeboard). May be modeled as weir flow over rider edge or riser notch. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 79 Chapter 2 2.2.3.2 BMP L631 Vegetated Rooftops (Green Roofs) Purpose and Definition Vegetated rooftops, also know as green roofs or eco-roofs, are veneers of living vegetation that are installed on top of conventional roofs. A green roof is an extension of the existing roof, which involves a special root repelling membrane, a drainage system, a lightweight growing medium, and plants. Vegetated walls and slopes may also be allowed. Applications and Limitations Vegetated rooftops offer a practical method of managing runoff in densely developed urban neighborhoods and can be engineered to achieve specific stormwater runoff control objectives. Design Guidelines • Soil or growth media must have a high field capacity. • Soil or growth media must have a saturated hydraulic conductivity of 1 inch/hour. • Drainage layer must allow free drainage under the soil/growth media. • Vegetative cover must be both drought and wet tolerant. • There must be a waterproof membrane between the drain layer and the structural roof support. • The maximum slope shall be 20%. Flow Credits for Vegetated Roofs Where vegetated roofs are used, the impervious areas may be modeled based on the thickness of the soil media: • For roofs with 3-8” of soil/growing media, model the roof as 50% till landscaped and 50% impervious. • For roofs with 8” of soil/growing media, model the roof as 50% till pasture and 50% impervious. Resource Material Miller, C. and Grantley Pyke. Methodology for the Design of Vegetated Roof Covers, Proceedings of the 1999 International Water Resources Engineering Conference, Seattle, Washington. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 80 Chapter 2 2.2.3.3 BMP L632 Rainfall Reuse Systems Purpose and Definition Rainfall reuse systems are designed to collect stormwater runoff from non-pollution generating surfaces and make use of the collected water. Rainfall reuse systems are also known as rainwater harvesting systems and rainfall catchment systems. Applications and Limitations Highly developed areas where large buildings encompass nearly all of the area. Approval of the water reuse system requires approval of the appropriate state and local agencies as required for any water right. Design Guidelines • Where captured water is solely for outdoor use, density shall be 4 homes per acre or less can be used. • Cisterns can be incorporated into the aesthetics of the building and garden. • If a rainwater reuse system holds more than 6 inches depth of water, it should be covered securely or have a top opening opening of 4 inches or less to prevent small children from gaining access to the standing water. • Design and maintain the system to minimize clogging by leaves and other debris. Flow Credits for Rainfall Reuse Systems The drainage area to the rainfall reuse system does not need to be entered into the runoff model when: • 100% of the annual average runoff volume (using WWHM) is reused, or • Interior uses have a monthly water balance that demonstrates adequate capacity for each month and reuse of all stored water annually. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 81 Chapter 2 2.2.3.4 BMP L633 Alternate Paving Surfaces Purpose and Definition Alternate paving surfaces include porous asphalt pavement, porous concrete, grid and lattice rigid plastic or paving blocks where the holes are filled with soil, sand, or gravel; and cast-in-place paver systems. Porous surfaces are designed to accommodate pedestrian, bicycle, and auto traffic while allowing infiltration and storage of stormwater. Alternate paving systems may be designed with an underdrain to collect stormwater or without an underdrain as an infiltration facility. Applications and Limitations • Appropriate application for alternative porous surfaces depend on the type of paving system, but typically include parking overflow areas, parking stalls, low volume residential roads, low-volume parking areas, alleys, driveways, sidewalks/pathways, and patios. • Porous paving surfaces surfaces can provide some attenuation and uptake of stormwater runoff even on cemented till soils while still providing the structural integrity required for a roadway surface to support heavy loads. • Porous paving surfaces work well in concert with other LID BMPs such as porous parking stalls adjacent to bioretention areas, and porous roadway surfaces bordered by vegetated swales. • Although there is a drop of infiltration rates over time, the long-term infiltration rate is still substantial enough to provide significant reductions in runoff. • Infiltration through pervious pavement surfaces shall not be allowed with land uses that generate heavy pollutant loads. The potential sediment loading for each application should be considered when determining if the application of alternate surfaces is appropriate. • Runoff generated from lawns or other pervious surfaces shall not be directed onto porous surfaces. • No point discharges may be directed to porous surfaces. • Sheet flow runoff may be directed onto a a porous surface provided that the length of sheet flow across the paved section is no more than twice the length of sheet flow across the porous pavement section. Design Criteria • Unless approved in writing by The City, maximum slopes for alternative paving surfaces are: o 5% for porous asphalt o 6% for porous concrete o 10% for interlocking pavers o 5-6% grid and lattice systems S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 82 Chapter 2 • Follow manufacturer’s recommendations for design, installation, and maintenance. • Subgrade infiltration rates less than 2.4 inches/hour and a cation exchange capacity of 5 milliequivalents CEC/100 grams dry soil (or greater) will provide water quality treatment. • Typical cross-sections of porous paving systems consist of: o A top layer with either porous asphalt, porous concrete, concrete block pavers, or a plastic grid paver filled with sand topsoil or gravel. o An aggregate subbase with larger rock at the bottom and smaller rock directly under the top surface. o For open-celled paving grids and blocks, a leveling course consisting of finer aggregate. o A geotextile fabric • Both gravel and soil with vegetation can be used to fill the opening in paver and rigid grid systems. Manufacturer recommendations should be followed to apply the appropriate material. • Porous systems that use pavers shall be confined with a rigid edge system to prevent gradual movement of the paving stones. • Subgrade layer: o Compact the subgrade to the minimum necessary for structural stability. Do not allow heavy compaction. The subgrade should not be subject to truck traffic. o Use on soil types A through C. • Geotextile o Use geotextile between subgrade and base material to keep soil out of base layer. o The geotextile must pass water at a greater rate than the subgrade soils. • Separation or Bottom Filter Layer (optional but recommended) o A layer of sand or crushed stone graded flat is recommended to promote infiltration across the surface, stabilize the base layer, protect the underlying soil from compaction, and serve as a transition between the base course and the underlying geotextile. • Base Material Material must be free draining. Below are examples of possible base material specifications. See Chapter 6 of the “Low Impact Development: Technical Guidance Manual for Puget Sound” for more detailed information. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 83 Chapter 2 Driveway base material: o >4” layer of free-draining crushed rock, screened gravel, or washed sand. o <5% fines (material passing the #200 sieve) based on fraction passing the #4 sieve. Roads and Parking Lots o Follow the standard material and quantities used for asphalt roads. • Wearing Layer o A minimum infiltration rate of 10 inches/hour is required though higher infiltration rates are desirable. o For porous asphalt, products must have adequate void space, commonly 12-20%. o For porous concrete, products must have adequate void space, commonly 15-21%. o For grid/lattice systems filled with gravel, sand, or a soil of finer particles with or without grass, fill must be at least 2”. Fill should be underlain with 6” or more of sand or gravel to provide an adequate base. Locate fill at or slightly below the top elevation the top elevation of the grid/lattice structure. Modular grid openings must be at least 40% of the total surface area. o For paving blocks, fill spaces between blocks with 6” of free draining sand or aggregate material. Provide a minimum of 12% free draining surface area. • Drainage Conveyance o Design roads with adequate drainage conveyance facilities if the road surface was impermeable. o Design drainage flow paths to move water safely away from the road prism and into the roadside drainage facility for roads with base courses that extend below the surrounding grade. • Acceptance Test o Test all permeable surfaces by throwing a bucket of water on the surface. If anything runs off the surface or puddles, additional testing is necessary prior to accepting the construction. o As directed by The City, test with a 6” ring infiltrometer or sprinkle infiltrometer. Wet the road surface continuously for 10 minutes. Test to determine compliance with 10 inches/hour minimum infiltration rate. o For facilities designed to infiltrate, the bucket test shall be completed annually. o Test documentation shall be retained with maintenance records. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 84 Chapter 2 Maintenance • Follow manufacturer’s suggestions for maintenance. • Inspect project upon completion to correct accumulation of fine material. Conduct periodic visual inspections to determine if surfaces are clogged. • Sweep non-planted surfaces with a high-efficiency sweeper twice per year, one in autumn, and one in early spring. Sweeping frequency can be reduced if infiltration rate testing indicates that a rate of 10 inches/hour or greater is being maintained. • Maintenance records shall be retained and provided to the City upon request. Flow Credits for Alternate Paving Systems Flow credits for alternate paving systems are based on the base material and type of alternate surface. The following lists the possible credits that can be achieved by using alternative paving systems: For porous asphalt or concrete systems used as public road or public parking lot configurations: Where base material is laid above surrounding grade: • Without an underdrain, model the surface as grass over underlying soil type. • With an underdrain either at or below the bottom of the base layer or elevated within the base course, model the surface as impervious. Where base material is laid partially or completely below surrounding grade: • Without an underdrain, model the surface as grass over underlying soil type or impervious surface routed to an infiltration. • With an underdrain at or below bottom of base layer or elevated within the base course, model the surface as impervious. For porous asphalt or concrete systems used at private facilities such as driveways, parking lots, walks, and patios: Where the base material is laid below ground: • Without an underdrain, model the surface as 50% grass on underlying soil and 50% impervious. • With a pipe underdrain, model the surface as impervious. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 85 Chapter 2 For grid/lattice systems and paving blocks used as public road or public parking lot: Where base material is laid above the surrounding grade: • Without an underdrain, model grid/lattice systems as grass on underlying soil and model paving blocks as 50% grass on underlying soil with 50% impervious. • With an underdrain, model the surface as impervious. Where base material is laid partially or completely below surround ground: • Without an underdrain, model grid/lattice systems as grass on underlying soil and model paving blocks as 50% grass with 50% impervious or model both grid/lattice systems and paving blocks as impervious surfaces routed to an infiltration basin. • With an underdrain, at or below bottom of the base layer, model the surface as impervious. With an underdrain elevated within the base course, model the surface as impervious routed to an infiltration basin. For grid/lattice systems and paving blocks used at private facilities (driveways, parking lots, walks, patios, etc.): Where base material is laid partially or completely below surrounding ground: • Without an underdrain, model the surface as 50% grass and 50% impervious. • With an underdrain, model the surface as impervious. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 86 Chapter 2 2.2.3.5 BMP L634 Minimal Excavation Foundations Purpose and Definition Minimal excavation foundation systems are those techniques that minimize disturbance to the natural soil profile within the footprint of the structure. This preserves most of the hydrologic properties of the native soil. Pin foundations are an example of a minimal excavation foundation. Applications Limitations • Suitable for pier and perimeter wall configurations for residential or commercial structures up to three stories high. • Useful for elevated paths and foot-bridges in environmentally sensitive areas. • Heavy equipment cannot be used within or immediately surrounding the building. Terracing of the foundation area may be accomplished by tracked, blading equipment not exceeding 650 psf. Design Criteria See Chapter 6 of “Low Impact Development: Technical Guidance Manual for Puget Sound” for design information. Flow Credits for Minimal Excavation Foundation Systems • Where roof runoff is dispersed on the up gradient side of a structure in accordance with the design criteria in “Downspout Dispersion”, model the tributary roof area as pasture on the native soil. • Where “step forming” is used on a slope, the square footage of roof that can be modeled as pasture must be reduced to account for lost soils. In “step forming,” the building area is terraced in cuts of limited depth. This results in a series of level plateaus on which to erect the form boards. The following equation can be used to reduce the roof area that can be modeled as pasture. A1 – dC(.5) X A1 = A2 dP A1 = roof area draining to up gradient side of structure dC = depth of cuts into the soil profile dP = permeable depth of soil (the A horizon plus an additional few inches of the B horizon where roots permeate into ample pore space of soil). A2 = roof area that can be modeled as pasture on the native soil • If roof runoff is is dispersed down gradient of the structure in accordance with the design criteria and guidelines “Downspout Dispersion”, and there is at least 50 feet of vegetated flow path through native material or lawn/landscape area that meets the guidelines in BMP L613 of Volume 5, Chapter 5, model the tributary roof areas as landscaped area. S U R F A C E W A T E R M A N A G E M E N T M A N U A L N O V E M B E R 2 0 0 9 Low Impact Development Volume VI Best Management Practices 7 87 Chapter 2 2.2.3.6 BMP L635 Reverse Slope Sidewalks Definition and Purpose Reverse slope sidewalks are sloped to drain away from the road and onto adjacent vegetated areas. Design Criteria for Reverse Slope Sidewalks • There must be 10 feet of vegetated surface downslope that is not directly connected into the storm drainage system. • Vegetated area receiving flow from sidewalk must be native soil or meet the guidelines in BMP L613: Post-Construction Soil Quality and Depth. Flow Credits for Reverse Slope Sidewalks • Model the sidewalk area as landscaped area over the underlying soil type. THIS PAGE INTENTIONALLY LEFT BLANK.