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HomeMy WebLinkAboutMunicipal Permit Appendix 201January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 1 of 30 APPENDIX 1 – Minimum Technical Requirements for New Development and Redevelopment Section 1. Exemptions Forest practices: Forest practices regulated under Title 222 WAC, except for Class IV General forest practices that are conversions from timber land to other uses, are exempt from the provisions of the minimum requirements. Commercial agriculture: Commercial agriculture practi ces involving working the la nd for production are generally exempt. However, the conversion from timberla nd to agriculture, and the construction of impervious surfaces are not exempt. Oil and Gas Field Activities or Operations: Construction of drilling sites, waste management pits, and access roads, as well as construction of transportation and treatment infrastructure su ch as pipelines natural gas treatment plants, natural gas pipeline compressor stations, and cr ude oil pumping stations are exempt. Operators are encouraged to implement and maintain Best Management Practices to minimize erosion and control sediment during and afte r construction activities to help ensure protection of surface water quality during storm events. Road Maintenance: The following road maintenance practices ar e exempt: pothole and square cut patching, overlaying existing asphalt or concrete pavement with asphalt or concrete without expanding the area of coverage, shoulder grading, reshaping/regrading drainage systems, crack sealing, resurfacing with in-kind material without expanding the road pris m, and vegetation maintenance. The following road maintenance practices are cons idered redevelopment, and therefore are not categorically exempt. The extent to which this Appendix applies is explained for each circumstance. • Removing and replacing a paved surface to ba se course or lower, or repairing the roadway base: If impervious surfaces ar e not expanded, Minimum Requirements #1 - #5 apply. However, in most cases, only Minimum Requirement #2, Construction Stormwater Pollution Prevention, will be germane. Where ap propriate, project proponents are encouraged to look for oppor tunities to use permeable and porous pavements. • Extending the pavement edge without increasin g the size of the road prism, or paving graveled shoulders: These are considered ne w impervious surfaces and are subject to the Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 2 of 30 minimum requirements that are triggered when the thresholds identified for redevelopment projects are met. • Resurfacing by upgrading from dirt to gravel, as phalt, or concrete; upgrading from gravel to asphalt, or concrete; or upgrading from a bituminous surface treatment (“chip seal”) to asphalt or concrete: These are considered new impervious surfaces and are subject to the minimum requirements that are triggered when the thresholds identified for redevelopment projects are met. Underground utility projects: Underground utility projects that replace the ground surface with in -kind material or materials with similar runoff characteristics are only s ubject to Minimum Requirement #2, Construction Stormwater Pollution Prevention. All other new development is subject to one or more of the Minimum Requirements (see Section 3 of this Appendix). Section 2. Definitions Related to Minimum Requirements Arterial - A road or street primarily for through tra ffic. A major arterial connects an Interstate Highway to cities and counties. A minor arte rial connects major arte rials to collectors. A collector connects an arterial to a neighborhood. A collector is not an arterial. A local access road connects individual homes to a collector. Certified Erosion and Sediment Control Lead (CESCL) - means an individual who has current certification through an approved er osion and sediment control training program that meets the minimum training standards established by the Department (see BMP C160 in the Stormwater Management Manual for Western Washington (2005)). A CESCL is knowledgeable in the principles and practices of eros ion and sediment control. The CESCL must have the skills to assess site conditions and construction activities th at could impact the quality of stormwater and, the effectiveness of erosion and sediment cont rol measures used to control the quality of stormwater discharges. Certification is obtained through an Ecol ogy approved erosion and sediment control course. Course listing ar e provided online at Ecology’s web site. Effective Impervious surface - Those impervious surfaces that ar e connected via sheet flow or discrete conveyance to a drainage system. Impe rvious surfaces on reside ntial development sites are considered ineffectiv e if the runoff is dispersed through at least one hundred feet of native vegetation in accordance with BMP T5.30 – “Full Dispersion,” as described in Chapter 5 of Volume V of the Stormwater Management Manual for Western Washington (2005). Highway – A main public road connecting towns and cities Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 3 of 30 Impervious surface - A hard surface area that either prevents or retards the entry of water into the soil mantle as under natural conditions prio r to development. A hard surface area which causes water to run off the surface in greater quantit ies or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, drivew ays, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly im pede the natural infiltration of stormwater. Open, uncovered retention/detention facilities shall not be cons idered as impervious surfaces for purposes of determining whether the thresholds for appli cation of minimum require ments are exceeded. Open, uncovered retention/detention facilities shall be considered impervious surfaces for purposes of runoff modeling. Land disturbing activity - Any activity that results in moveme nt of earth, or a change in the existing soil cover (both vegetative and non-vege tative) and/or the existing soil topography. Land disturbing activities include, but are not limited to clearing, grading, filling, and excavation. Compaction that is a ssociated with stabilization of structures and road construction shall also be considered a land disturbing activity. Vegetation maintenance practices are not considered land-disturbing activity. Maintenance - Repair and maintenance includes activ ities conducted on currently serviceable structures, facilities, and equipment that involv es no expansion or use beyond that previously existing and results in no signifi cant adverse hydrologic impact. It includes those usual activities taken to prevent a decline, lapse, or cessation in the use of structures a nd systems. Those usual activities may include replacem ent of dysfunctional facilities, including cases where environmental permits require replacing an existing structure with a different type structure, as long as the functioning characterist ics of the original structure ar e not changed. One example is the replacement of a collapsed, fish blocki ng, round culvert with a new box culvert under the same span, or width, of roadway. See also Road Maintenance exemptions in Section 1 of this Appendix. Native vegetation – Vegetation comprised of plant species, other than noxious weeds, that are indigenous to the coastal region of the Pacific No rthwest and which reasonably could have been expected to naturally occur on th e site. Examples include trees such as Douglas Fir, western hemlock, western red cedar, alder, big-leaf maple, and vine ma ple; shrubs such as willow, elderberry, salmonberry, and salal; and herbaceous pl ants such as sword fern, foam flower, and fireweed. New development - Land disturbing activities, including Class IV -general forest practices that are conversions from timber land to other uses; structural devel opment, including construction or installation of a building or othe r structure; creation of imperv ious surfaces; and subdivision, short subdivision and binding site plans, as de fined and applied in Chapter 58.17 RCW. Projects meeting the definition of redevelopment sh all not be considered new development. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 4 of 30 Pollution-generating impervious surface (PGIS) - Those impervious surfaces considered to be a significant source of pollutants in stormwater ru noff. Such surfaces include those which are subject to: vehicular use; industria l activities (as further defined in the glossary); or storage of erodible or leachable materials, wastes, or chemical s, and which receive direct rainfall or the run-on or blow-in of rainfall. Erodible or leachab le materials, wastes, or chemicals are those substances which, when exposed to rainfall, measurably alter the physical or chemical characteristics of the rainfall runoff. Exampl es include erodible soils that are stockpiled, uncovered process wastes, manure, fertilizers, oily substances, ashes, kiln dust, and garbage dumpster leakage. Metal roofs ar e also considered to be PGIS unless they are coated with an inert, non-leachable material (e.g., baked-on enamel coating). A surface, whether paved or not, shall be consider ed subject to vehicular use if it is regularly used by motor vehicles. The following are c onsidered regularly-used surfaces: roads, unvegetated road shoulders, bike la nes within the traveled lane of a roadway, driveways, parking lots, unfenced fire lanes, ve hicular equipment storage yard s, and airport runways. The following are not considered regularly-used surfaces: paved bicycle pathways separated from and not subject to drainage from roads for motor vehicles, fenced fire lanes, and infrequently used maintenance access roads. Pollution-generating pervious surfaces (PGPS) - Any non-impervious surf ace subject to use of pesticides and fertilizers or loss of soil. T ypical PGPS include lawns, landscaped areas, golf courses, parks, cemeteries, and sports fields. Pre -developed condition – The native vegetation and soils that existed at a site prior to the influence of Euro-American settlement. The pre-developed condition shall be assumed to be a forested land cover unless reasonab le, historic information is provi ded that indicates the site was prairie prior to settlement. Project site - That portion of a property, properties, or right of way subject to land disturbing activities, new impervious surfaces , or replaced impervious surfaces. Receiving waters - Bodies of water or surface water sy stems to which surface runoff is discharged via a point source of stormwater or via sheet flow. Redevelopment - On a site that is already substantially developed (i.e., has 35% or more of existing impervious surface coverage), the crea tion or addition of impervious surfaces; the expansion of a building footprint or addition or replacement of a structure; structural development including construction, installation or expans ion of a building or other structure;; replacement of impervious surface that is not part of a routine maintenance activity; and land disturbing activities. Replaced impervious surface - For structures, the removal and replacement of any exterior impervious surfaces or foundation. For other impe rvious surfaces, the removal down to bare soil or base course and replacement. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 5 of 30 Site – The area defined by the legal boundaries of a parcel or parcels of land that is (are) subject to new development or redevelopment. For road projects, the length of th e project site and the right-of-way boundaries define the site. Source control BMP - A structure or operation that is intended to prevent pollutants from coming into contact with stormwater thr ough physical separation of areas or careful management of activities that are sources of po llutants. This manual se parates source control BMPs into two types. Structural Source Control BMPs are physical, structural, or mechanical devices, or facilities that are intended to prevent pollutants from entering stormwater. Operational BMPs are non-structural practices that prev ent or reduce pollutants from entering stormwater. See Volume IV of the Stormwater Management Manual for Western Washington (2005) for details. Threshold Discharge Area - An onsite area draining to a singl e natural discharge location or multiple natural discharge locations that comb ine within one-quarter mile downstream (as determined by the shortest flowpath). The exam ples in Figure 2.1 below illustrate this definition. The purpose of this definition is to clarify how the thresholds of this manual are applied to project sites with multiple discharge points. Wetland - Those areas that are inundated or satura ted by surface or ground water at a frequency and duration sufficient to support, and that unde r normal circumstances do support, a prevalence of vegetation typically adapted for life in satu rated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. Wetla nds do not include those artificial wetlands intentionally created from non-we tland sites, including, but not limite d to, irrigation and drainage Figure 2.1 Threshold Discharge Areas Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 6 of 30 ditches, grass-lined swales, canal s, detention facilities, wastewat er treatment facilities, farm ponds, and landscape amenities, or those wetlands created after July 1, 1990, that were unintentionally created as a result of the construction of a road, street, or highway. Wetlands may include those artificial wetlands intentionally created from non-wetland areas to mitigate the conversion of wetlands. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 7 of 30 Section 3. Applicability of the Minimum Requirements 3.1 Thresholds Not all of the Minimum Requirements appl y to every development or redevelopment project. The applicability varies depending on the type and size of the project. This section identifies thresholds that determine the applicability of the Minimum Requirements to different projects. The flow charts in Figures 3.1, 3.2 and 3.3 must be used to determine which of the Min imum Requirements a pply. The Minimum Requirements themselves are presente d in Section 4 of this Appendix. The thresholds below apply to new developm ent, redevelopment, and construction site activities that result in land disturbance of equal or greater than one acre, including projects less than one acre that are part of a larger common plan of development or sale. This threshold is defined as the “regulatory th reshold”. If as described above, the project exceeds the one acre regulatory threshold, the technical thresholds contained in this section (Section 3) shal l be applied by the Permittee to determine which of the minimum requirements must be applied to the project. Permittees whose ordinances at the time of permit issuance, regulate new development and redevelopment at sites be low the regulatory threshold mu st continue to regulate stormwater from these project sites. Fo r these project sites below the regulatory threshold, the permittee must continue to apply the local stormwater requirements in effect at the time of permit issuance or apply the minimum requirements for new development and re-development contained in this Appendix. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 8 of 30 Will the project disturb 1 acre or more? Or If the project disturbs less than 1 acre, is it part of a larger common plan of development or sale? Continue with Figures 3.2 and 3.3 Yes Yes Permittee is not required to apply the Minimum Requirements to the project. No No Figure 3.1 Flow Chart for Determining Whether the Permittee Must Regulate the Project Prior to the issuance of this permit did the Permittee regulate stormwater from project sites disturbing less than 1 acre? Yes This permit does require the Permittee to regulate stormwater from the site. No START Is the project site exempt according to Section 1 of this Appendix? Yes No Will the project site discharge stormwater either directly or indirectly into an MS4 owned or operated by the Permittee? Continue to regulat e stormwater from the project site under local stormwater requirements in effect at the time of permit issuance. Or Apply the minimum requirements for new development and redevelopment as outlined in Figures 3.2 and 3.3. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 9 of 30 Start Here Figure 3.2 Flow Chart for Determi ning Requirements for New Development Does the site have 35% or more of existing impervious coverage? See Redevelopment Minimum Requirements and Flow Chart (Figure 2.3) Does the project add 5,000 square feet or more of new impervious surfaces? Does the project convert ¾ acres of native vegetation to lawn or landscaped areas, or convert 2.5 acres of native vegetation to pasture?All Minimum Requirements apply to the new impervious surfaces and converted pervious surfaces. Y es No Yes Yes No No Does the project have 2,000 square feet or more of new, replaced, or new plus replaced impervious surfaces?Does the project have land-disturbing activities of 7,000 square feet or more? Minimum Requirements #1 through #5 apply to the new and replaced impervious surfaces and the land disturbed. See Minimum Requirement #2, Construction Stormwater Pollution Prevention Y es No Y es No Does the project convert ¾ acres or more of native vegetation to lawn or landscaped areas, or convert 2.5 acres or more of native vegetation to pasture? See Redevelopment Minimum Requirements and Flow Chart (Figure 3.3) Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 10 of 30 Figure 3.3 Flow Chart for Determi ning Requirements for Redevelopment Apply Minimum Requirement #2, Construction Stormwater Pollution Prevention Does the project add 5,000 square feet or more of new impervious surfaces? OR Convert ¾ acres or more of native vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? Minimum Requirements #1 through #5 apply to the new and replaced impervious surfaces and the land disturbed. Do the new, replaced, or new plus replaced impervious surfaces total 2,000 square feet or more? OR Does the land disturbing activity total 7,000 square feet or more? Minimum Requirements #1 through #10 apply to the new impervious surfaces and the converted pervious surfaces. Does the project add 5,000 square feet or more of new impervious surfaces? Is the total of the new plus replaced impervious surfaces 5,000 square feet or more, AND does the value of the p roposed improvements – including interior improvements – exceed 50% of the assessed value (or replacement value) of the existing site improvements? No additional requirements Do new impervious surfaces add 50% or more to the existing impervious surfaces within the project limits? No additional requirements Minimum Requirements #1 through #10 apply to the new and replaced impervious surfaces. Yes No Next Question Yes Yes Y es Yes Next Question No No No No Is this a road-related project? Y es No Minimum Requirements #1 through #9 apply to the new impervious surfaces and the converted pervious surfaces Minimum Requirements #1 through #9 apply to the new and replaced impervious surfaces Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 11 of 30 3.2 New Development All new development shall be required to comply with Minimum Requirement #2. The following new development shall comply with Minimum Requirements #1 through #5 for the new and replaced impervious surfaces and the land disturbed: • Creates or adds 2,000 square feet, or greater, of new, replaced, or new plus replaced impervious surface area, or • Has land disturbing activity of 7,000 square feet or greater, The following new development shall comply with Minimum Requirements #1 through #10 for the new impervious surfaces a nd the converted pervious surfaces: • Creates or adds 5,000 square feet, or more, of new impervious surface area, or • Converts ¾ acres, or more, of native vegetation to lawn or landscaped areas, or • Converts 2.5 acres, or more, of native vegetation to pasture. 3.3 Redevelopment All redevelopment shall be required to comply with Minimum Requirement #2. In addition, all redevelopment that exceeds certain thresholds shall be required to comply with additional Minimum Requirements as follows. The following redevelopment shall comply with Minimum Requirements #1 through #5 for the new and replaced impervious surfaces and the land disturbed: • The new, replaced, or total of new plus rep laced impervious surfaces is 2,000 square feet or more, or • 7,000 square feet or more of land disturbing activities. The following redevelopment shall comply with Minimum Requirements #1 through #10 for the new impervious surfaces and converted pervious areas: • Adds 5,000 square feet or more of new impervious surfaces or, • Converts ¾ acres, or more, of native vegetation to lawn or landscaped areas, or • Converts 2.5 acres, or more, of native vegetation to pasture. If the runoff from the new impervious surf aces and converted pervious surfaces is not separated from runoff from other surfaces on th e project site, the st ormwater treatment facilities must be sized for the entire flow that is directed to them. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 12 of 30 The local government may allow the Minimum Requirements to be met for an equivalent (flow and pollution characteristics) area within the same site. For public roads' projects, the equivalent area does not have to be with in the project limits, but must drain to the same receiving water. 3.4 Additional Requirements for Re-development Project Sites For road-related projects, runoff from the replaced and new impervious surfaces (including pavement, shoulders, curbs, and sidewalks) shall meet all the Minimum Requirements if the new impervious surfaces total 5,000 square feet or more and total 50% or more of the existing impervious surf aces within the project limits. The project limits shall be defined by th e length of the project and the width of the right–of-way. Other types of redevelopment projects shall comply with all the Minimum Requirements for the new and replaced impervious surfaces if the total of new plus replaced impervious surfaces is 5,000 square feet or more, a nd the valuation of proposed improvements – including interior improvements – exceeds 50% of the assessed value of the existing site improvements. The Permittee may exempt or institute a st op-loss provision for redevelopment projects from compliance with Minimum Requirements fo r treatment, flow control, and wetlands protection as applied to the replaced imperv ious surfaces if the Permittee has adopted a plan and a schedule that fulfills those requirements in regional facilities. See also Sections 5, 6 and 7 of this Appendix. The Permittee may grant a variance/exception to the application of the flow control requirements to replaced impervious surfaces if such application imposes a severe economic hardship. See Secti on 6 of this Appendix. 3.5 Modification of the Minimum Requirements Basin Planning is encouraged and may be used to tailor Mi nimum Requirement #6 Runoff Treatment, Minimum Requirement #7 Flow Cont rol, and/or Minimum Requirement #8 Wetlands Protection. Basin pl anning may be used to support alternative treatment, flow control, and/or wetland pr otection requirements to those contained in Section 4 of this Appendix. Basin planni ng may also be used to demonstrate an equivalent level of treatment, flow c ontrol, and/or wetland protection through the construction and use of regional stormwater facilities. See Se ction 7 of this Appendix for details on Basin Planning and how basin pla nning may be used to modify the Minimum Requirements is Section 4. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 13 of 30 Section 4. Minimum Requirements This Section describes the Minimum Requi rements for stormwater management at development and redevelopment sites. Secti on 3 of this Appendix should be consulted to determine which of the minimum requirements be low apply to any given project. Figures 3.2 and 3.3 should be consulted to determine whether the minimum requirements apply to new surfaces, replaced surfaces or new and replaced surfaces. 4.1 Minimum Requirement #1: Preparation of Stormwater Site Plans The permittee shall require a Stormwater Si te Plan from all projects meeting the thresholds in Section 3.1 of this Appendix. St ormwater Site Plans shall be prepared in accordance with Chapter 3 of Volume 1 of the Stormwater Manage ment Manual for Western Washington (2005). 4.2 Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan (SWPPP ) Permittees may choose to allow compliance with this Minimum Requirement to be achieved for an individual site if the site is covered under Ecology’s General NPDES Permit for Stormwater Discharges Asso ciated with Construction Activities and fully implementing the requirements of that permit. Permittees may choose to allow site operators to apply an “Erosivity Waiver” to projects disturbing less than five acres that meet the re quirements at the end of this section; such projects would be waived from the requireme nt that the Permittee review site plans for construction phase stormwater pollution prevention. General Requirements All new development and redevelopment proj ects are responsible for preventing erosion and discharge of sediment and other pollutant s into receiving waters. Permittees must require a Construction S tormwater P ollution P revention P lan (SWPPP) as part of the Stormwater Site Plan (see Minimum Require ment #1 above) for all projects which meet the thresholds in Section 3 of this Appendix. The SWPPP shall be implemented beginning with initial soil disturbanc e and until final stabilization. Sediment and Erosion control BMPs shall be consistent with the BMPs contained in chapters 3 and 4 of Volume II of the Stormwater Management Manual for Western Washington (2005), and/or other equivalent BMPs contained in technical stormwater manuals approved by the Department. The SWPPP shall include a narrative and drawin gs. All BMPs shall be clearly referenced in the narrative and marked on the draw ings. The SWPPP narrative shall include documentation to explain and justify the pol lution prevention decisions made for the project. Clearing and grading activities for developments shall be permitted only if Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 14 of 30 conducted pursuant to an approved site deve lopment plan (e.g., subdivision approval) that establishes permitted areas of clearing, gradi ng, cutting, and filling. When establishing these permitted clearing and grading areas, cons ideration should be given to minimizing removal of existing trees and minimizing di sturbance/compaction of native soils except as needed for building purposes. These permitted clearing and grading areas and any other areas required to preser ve critical or sensitive ar eas, buffers, native growth protection easements, or tree retention areas as may be required by local jurisdictions, shall be delineated on the site plans and the development site. Seasonal Work Limitations - From October 1 through Apr il 30, clearing, grading, and other soil disturbing activities may only be au thorized by the Permittee if silt-laden runoff will be prevented from leaving the site through a combination of the following: 1. Site conditions including existing vegetative coverage, slope, soil type and proximity to receiving waters; and 2. Limitations on activities and the ex tent of disturbed areas; and 3. Proposed erosion and sediment control measures. Based on the information provided and/or local weather conditions, the Permittee may expand or restrict the seasonal limitation on si te disturbance. The following activities are exempt from the seasonal cl earing and grading limitations: 1. Routine maintenance and necessary repair of erosion and sediment control BMPs, 2. Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil, and 3. Activities where there is one hundred per cent infiltration of surface water runoff within the site in approved and installe d erosion and sediment control facilities. Construction Stormwater Pollution Prevention Plan (SWPPP) Elements The construction site operator shall include each of the twelve elements below in the SWPPP and ensure that they are implemente d unless site conditions render the element unnecessary and the exemption from that elemen t is clearly justified in the SWPPP. The SWPPP shall include both narrativ e and drawings. All BMPs shall be clearly referenced in the narrative and marked on the draw ings. The SWPPP narrative shall include documentation to explain and justify the pol lution prevention decisions made for the project. 1. Preserve Vegetation/Mark Clearing Limits: a Prior to beginning land disturbing ac tivities, including cl earing and grading, clearly mark all clearing limits, sensitive ar eas and their buffers, and trees that are to be preserved within the construction area. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 15 of 30 b. The duff layer, native top soil, and natu ral vegetation shall be retained in an undisturbed state to the ma ximum degree practicable. 2. Establish Construction Access : a. Construction vehicle access and exit sha ll be limited to one route, if possible. b. Access points shall be stabilized with quarry spalls, crushed rock or other equivalent BMP to minimize the tracki ng of sediment onto public roads. c. Wheel wash or tire baths shall be loca ted on site, if the stab ilized constructions entrance is not effective in preventing sediment from being tracked onto public roads. d. If sediment is tracked off site, roads sha ll be cleaned thoroughly at the end of each day, or more frequently during wet weather. Sediment shall be removed from roads by shoveling or pickup sweeping and shall be transported to a controlled sediment disposal area. e. Street washing is allowed only after se diment is removed in accordance with 2.d, above. Street wash wastewater shall be controlled by pumping back on site or otherwise be prevented from discharging in to systems tributary to waters of the state. 3. Control Flow Rates : a. Properties and waterways downstream from development sites shall be protected from erosion due to increases in the velo city and peak volumetric flow rate of stormwater runoff from the project site. b. Where necessary to comply with 3.a, a bove, stormwater retention or detention facilities shall be construc ted as one of the first st eps in grading. Detention facilities shall be function al prior to construction of site improvements (e.g., impervious surfaces). c. If permanent infiltration ponds are used for flow control during construction, these facilities should be protected fro m siltation during the construction phase. 4. Install Sediment Controls : a. Stormwater runoff from disturbed areas shall pass through a sediment pond, or other appropriate sediment removal BMP, prior to leaving a construction site or prior to discharge to an infiltration faci lity. Runoff from fu lly stabilized areas may be discharged without a sediment removal BMP, but shall meet the flow control performance standard of 3.a, above. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 16 of 30 b. Sediment control BMPs (sed iment ponds, traps, filters, etc.) shall be constructed as one of the first steps in grading. Th ese BMPs shall be functional before other land disturbing activities take place. c. BMPs intended to trap sedi ment on site shall be located in a manner to avoid interference with the moveme nt of juvenile salmonids attempting to enter off-channel areas or drainages. 5. Stabilize Soils : a. Exposed and unworked soils shall be st abilized by application of effective BMPs that prevent erosion. b. No soils should remain exposed and unworked for more than the time periods set forth below to prevent erosion: • During the dry season (May 1 – September 30): 7 days • During the wet season (October 1 – April 30): 2 days c. The time period may be adjusted by the Permittee, if the Permittee can show that local precipitation data jus tify a different standard. d. Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. e. Soil stockpiles must be stab ilized from erosion, protec ted with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways and drainage channels. 6. Protect Slopes : a. Design and construct cut and fill slopes in a manner that will minimize erosion. b. Off-site stormwater (run-on) or groundwater shall be diverted away from slopes and undisturbed areas with interceptor di kes, pipes and/or swales. Off-site stormwater should be managed separately from stormwater generated on the site. c. At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. Temporary pipe slope drai ns shall handle th e expected peak 10-minute flow velocity from a Type 1A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10-year, 1-hour flow rate predicted by an approved continuous runoff model, increas ed by a factor of 1.6, may be used. The hydrologic analysis shall use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis shall use the temporary or permanent project land cover condition, whichever will produce th e highest flow rates. If using the Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 17 of 30 Western Washington Hydrology Model to pred ict flows, bare soil areas should be modeled as “landscaped area.” d. Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations. e. Check dams shall be placed at regular intervals within constructed channels that are cut down a slope. 7. Protect Drain Inlets : a. Storm drain inlets made operable during construction shall be protected so that stormwater runoff does not enter the c onveyance system without first being filtered or treated to remove sediment. b. Inlet protection devices shall be cleaned or removed and replaced when sediment has filled one-third of the available storage (unless a different standard is specified by the product manufacturer). 8. Stabilize Channels and Outlets : a. All temporary on-site conveyance channe ls shall be designed, constructed, and stabilized to prevent erosion from the fo llowing expected peak flows. Channels shall handle the expected peak 10-minute fl ow velocity from a Type 1A, 10-year, 24-hour frequency storm for the develope d condition. Alternatively, the 10-year, 1-hour flow rate predicted by an approve d continuous runoff model, increased by a factor of 1.6, may be used. The hydrologi c analysis shall use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project s ite, the analysis shall use the temporary or permanent project land cover cond ition, whichever will produce the highest flow rates. If using the Western Wash ington Hydrology Model to predict flows, bare soil areas should be mode led as “landscaped area.” b. Stabilization, including armoring material , adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downst ream reaches shall be provided at the outlets of all conveyance systems. 9. Control Pollutants : a. All pollutants, including waste material s and demolition debris, that occur onsite shall be handled and disposed of in a ma nner that does not cause contamination of stormwater. b. Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum produc ts, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks shall include seco ndary containment. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 18 of 30 c. Maintenance, fueling and repair of heavy equipment and vehicles shall be conducted using spill prevention and cont rol measures. Contaminated surfaces shall be cleaned immediately following any spill incident. d. Wheel wash or tire bath wastewater shall be discharg ed to a separate on-site treatment system or to the sanitary sewer with local sewer district approval. e. Application of fertilizer s and pesticides shall be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers’ label requirements for appl ication rates and procedures shall be followed. f. BMPs shall be used to prevent or trea t contamination of stormwater runoff by pH modifying sources. These sources include , but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. Permittees shall require construction site op erators to adjust the pH of stormwater if necessary to prev ent violations of wa ter quality standards. g. Permittees shall require construction site operators obtain written approval from the Department prior to using chemical treatment other than CO2 or dry ice to adjust pH. 10. Control De-Watering : a. Foundation, vault, and trench de-w atering water, which have similar characteristics to stormwater runoff at the site, shall be discharged into a controlled conveyance system prior to disc harge to a sediment trap or sediment pond. b. Clean, non-turbid de-watering water, such as well-point ground water, can be discharged to systems tributary to, or dire ctly into surface waters of the state, as specified in 8, above, provided the de-wat ering flow does not cause erosion or flooding of receiving waters. Clean de-w atering water should not be routed through stormwater sediment ponds. c. Other de-watering disposal options may include: (i) infiltration; (ii) transport offsite in vehicle, such as a vacuum flus h truck, for legal disposal in a manner that does not pollute state waters ; (iii) on-site chemical tr eatment or other suitable treatment technologies approved by the Perm ittee; (iv) sanitary sewer discharge with local sewer district approval, if th ere is no other option; or (v) use of a sedimentation bag with outfall to a ditch or swale for small vol umes of localized de-watering. d. Highly turbid or contaminated dewatering water shall be handled separately from stormwater. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 19 of 30 11. Maintain BMPs : a. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired as need ed to assure contin ued performance of their intended function in accordan ce with BMP specifications. b. All temporary erosion and sediment c ontrol BMPs shall be removed within 30 days after final site stabilization is ac hieved or after the temporary BMPs are no longer needed. 12. Manage the Project : a. Development projects shall be phased to the maximum degree practicable and shall take into account seasonal work limitations. b. The Permittee must require construction site operators to maintain, and repair as needed, all sediment and erosion control BMPs to assure continued performance of their intended function. c. The Permittee must require construction si te operators to periodically inspect their sites. Site inspections sh all be conducted by a Certif ied Erosion and Sediment Control Lead who shall be identified in the SWPPP and shall be present on-site or on-call at all times. d. Permittee must require construction s ite operators to maintain, update and implement their SWPPP. Permittees shall require construction site operators to modify their SWPPP when ever there is a change in design, construction, operation, or maintenance at the construction s ite that has, or could have, a significant effect on the di scharge of pollutants to waters of the state. Erosivity Waiver Permittees may allow construction site op erators to qualify for a waiver from the requirement to submit a SWPPP for revi ew by the Permittee provided the following conditions are met: 1. The site will result in the disturbance of less than 5 acres; and th e site is not a portion of a common plan of development or sale that will disturb 5 acres or greater; and 2. The project’s rainfall erosivity factor (“R” Factor) is less than 5 during the period of construction activity, as calculated using the Texas A&M University online rainfall erosivity calculator at: http://ei.tamu.edu /. The period of construction activity begins at initial earth disturbance and e nds with final stabilization; and 3. The entire period of construction activity falls between June 15 and September 15; and Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 20 of 30 4. The site or facility has not been declared a significant contributor of pollutants; and 5. There are no planned construction activities at the site that will result in non-stormwater discharges; and 6. A waiver is allowed by the Permittee; and 7. The construction site operators notify the Permittee of the intention to apply this waiver at least one week prior to co mmencing land disturbing activities. The notification must include a su mmary of the project information used in calculating the project’s rainfall erosivity factor (see #2 above) and a certified statement that: • The operator will comply with applicable local stormwater requirements; and • The operator will implement appropriate erosion and sediment control BMPs to prevent violations of water quality standards. 4.3 Minimum Requirement #3: So urce Control of Pollution All known, available and reasonable source cont rol BMPs must be required for to all projects approved by the Permittee. Source control BMPs must be selected, designed, and maintained in accordance with Volume IV of the Stormwater Management Manual for Western Washington (2005) or an approved equiva lent manual approved by the Department. 4.4 Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls Natural drainage patterns shall be maintaine d, and discharges from the project site shall occur at the natural location, to the maximu m extent practicable. The manner by which runoff is discharged from the project site mu st not cause a significant adverse impact to downstream receiving waters and down gradient properties. All out falls require energy dissipation. 4.5 Minimum Requirement #5: On-s ite Stormwater Management The Permittee must require On-site Stormwater Management BMPs to infiltrate, disperse, and retain stormwater runoff onsite to th e maximum extent feasible without causing flooding or erosion impacts. Roof Downspout Control BMPs, functionally equivalent to those described in Chapter 3 of Volume III of the Stormwater Management Manual for Western Washington (2005), and Dispersion and So il Quality BMPs, functionally equivalent to those in Chapter 5 of Volume V, of the Stormwater Management Manual for Western Washington (2005) shall be required to re duce the hydrologic disruption of developed sites. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 21 of 30 4.6 Minimum Requirement #6: Runoff Treatment Project Thresholds The following require construction of stormw ater treatment facilities (see Table 4.1 below): • Projects in which the total of effectiv e, pollution-generating impervious surface (PGIS) is 5,000 square feet or more in a threshold discharge area of the project, or • Projects in which the total of pollution-generating pervious surfaces (PGPS) is three-quarters (3/4) of an acre or more in a threshold discharge area, and from which there is a surface di scharge in a natural or man-made conveyance system from the site. PGPS = pollution-generating pervious surfaces PGIS = pollution-generating impervious surfaces sf = square feet Treatment -Type Thresholds 1. Oil Control: Treatment to achieve Oil Cont rol applies to projects that have “high-use sites.” High-use sites are those that typically generate high con centrations of oil due to high traffic turnover or the frequent transfer of oil. High-use sites include: a. An area of a commercial or industria l site subject to an expected average daily traffic (ADT) count equal to or greater than 100 vehicles per 1,000 square feet of gross building area; b. An area of a commercial or industria l site subject to petroleum storage and transfer in excess of 1,500 gallons per year, not including routinely delivered heating oil; c. An area of a commercial or industr ial site subject to parking, storage or maintenance of 25 or more vehicles that are over 10 tons gross weight (trucks, buses, trains, heavy equipment, etc.); Table 4.1 Treatment Requirements by Threshold Discharge Area < ¾ acres of PGPS > ¾ acres PGPS < 5,000 sf PGIS > 5,000 sf PGIS Treatment Facilities a b Onsite Stormwater BMPs a a b a Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 22 of 30 d. A road intersection with a measur ed 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 prim arily pedestrian or bicycle use improvements. 2. Phosphorus Treatment: The requirement to provide phosphorous control is determined by the local government with jurisdiction (e.g., through a lake management plan), or the Department of Ecology (e.g, through a wa ste load allocation). The local government may have developed a management plan and implementing ordinances or regulations for control of phosphorus from new/redevelopment for the receiving water(s) of the stormwater drainage. The local government can use the following sources of informati on for pursuing plans and implementing ordinances and/or regulations: a. Those waterbodies reported under se ction 305(b) of the Clean Water Act, and designated as not supporting benefi cial uses due to phosphorous; b. Those listed in Washington State's Nonpoint Source Assessment required under section 319(a) of the Clean Water Act due to nutrients. 3. Enhanced Treatment: Enhanced treatment for reduction in dissolv ed metals is required for the following project sites that discharge to fish-bea ring streams, lakes, or to waters or conveyance systems tributary to fish-bearing streams or lakes: Industrial project sites, Commercial project sites, Multi-family project sites, and High AADT roads as follows: Within Urban Growth Management Areas: • Fully controlled and partially controlled limited access highways with Annual Average Daily Traffic (AADT) counts of 15,000 or more • All other roads with an AADT of 7,500 or greater Outside of Urban Growth Management Areas: • Roads with an AADT of 15,000 or greater unless discharging to a 4 th Strahler order stream or larger; • Roads with an AADT of 30,000 or gr eater if discharging to a 4 th Strahler order stream or larger (as determ ined using 1:24,000 scale maps to delineate stream order). Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 23 of 30 However, such sites listed above that di scharge directly (or, indirectly through a municipal storm sewer system) to Basic Treatment Receiving Waters (Appendix I-C of the Stormwater Management Manual for Western Washington (2005)), and areas of the above-listed project sites th at are identified as subject to Basic Treatment requirements, are also not subject to Enhanced Treatment requirements. For developments with a mix of land use types, the Enhanced Treatment requirement shall apply when th e runoff from the areas subject to the Enhanced Treatment requirement comprise 50% or more of the total runoff within a threshold discharge area. 4. Basic Treatment: Basic Treatment generally applies to: • Project sites that discha rge to the ground, UNLESS: 1) The soil suitability criteria for infiltration treatment are met; (see Chapter 3 of Volume III of the Stormwater Management Manual for Western Washington (2005) for soil suitability criteria) or 2) The project uses infiltration strict ly for flow control – not treatment - and the discharge is within ¼-mile of a phosphorus sensitive lake (use a Phosphorus Treatment facility), or within ¼ mile of a fish-bearing stream, or a lake (use an E nhanced Treatment facility). • Residential projects not otherwis e needing phosphorus control as designated by USEPA, the Department of Ecology, or by the Permittee; and • Project sites discharging directly to salt waters, river segments, and lakes listed in Appendix I-C of the Stormwater Management Manual for Western Washington (2005); and • 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 that do not involve pollution-generating sources (e.g., industrial activ ities, customer parking, storage of erodible or leachab le material, wastes or chemicals) other than parking of employees’ privat e vehicles. 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 comprise 50% or more of the total runoff within a threshold discharge area. Treatment Facility Sizing Water Quality Design Storm Volume: The vol ume of runoff predicted from a 24-hour storm with a 6-month return frequency (a.k.a., 6-month, 24-hour storm). Wetpool Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 24 of 30 facilities are sized based upon the volume of runoff predicte d through use of the Natural Resource Conservation Service curve number equa tions in Chapter 2 of Volume III of the Stormwater Management Manual for Western Washington (2005), for the 6-month, 24-hour storm. Alternatively, the 91 st percentile, 24-hour runoff volume indicated by an approved continuous runoff model may be used. Water Quality Design Flow Rate 1. Preceding Detention Facilities or when Dete ntion Facilities are not required: The flow rate at or below which 91% of the runoff volume, as estimated by an approved continuous runoff model, will be treated. Design criteria for treatment facilities are assigned to achieve the a pplicable performance goal at the water quality design flow rate (e.g., 80% TSS removal). 2. Downstream of Detention Facilities: The water quality design flow rate must be the full 2-year release rate from the detention facility. Alternative methods may be used if they identify volumes and flow rates that are at least equivalent. That portion of any development pr oject in which the above PGIS or PGPS thresholds are not exceeded in a threshold discharge area shall apply On-site Stormwater Management BMPs in accordance with Minimum Requirement #5. Treatment Facility Selection, Design, and Maintenance Stormwater treatment facilities shall be: • Selected in accordance with the process id entified in Chapter 4 of Volume I of the Stormwater Management Manual for Western Washington (2005), • Designed in accordance with the desi gn criteria in Volume V of the Stormwater Management Manual for Western Washington (2005), and • Maintained in accordance with the main tenance schedule in Volume V of the Stormwater Management Manual for Western Washington (2005). Additional Requirements The discharge of untreated stormwater from pollution-generating impervious surfaces to ground water must not be authorized by the Pe rmittee, except for the discharge achieved by infiltration or dispersion of runoff from residential sites th rough use of On-site Stormwater Management BMPs. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 25 of 30 4.7 Minimum Requirement #7: Flow Control Applicability Except as provided below, the Permittee must re quire all projects provide flow control to reduce the impacts of stormwater runoff fr om impervious surfaces and land cover conversions. The requirement below applies to projects that di scharge stormwater directly, or indirectly through a conve yance system, into a fresh water. Flow control is not required for projects that discharge direc tly to, or indirectly through an MS4 to a water listed in Appendix I-E of the Stormwater Management Manual for Western Washington (2005) subject to the fo llowing restrictions: • Direct discharge to the exempt receiving wa ter does not result in the diversion of drainage from any perennial stream classifi ed as Types 1, 2, 3, or 4 in the State of Washington Interim Water Typing System, or Types “S”, “F”, or “Np” in the Permanent Water Typing System, or from a ny category I, II, or III wetland; and • Flow splitting devices or drai nage BMP’s are applied to route natural runoff volumes from the project site to any downstream Type 5 stream or category IV wetland: o Design of flow splitting devices or drainage BMP’s will be based on continuous hydrologic modeling analysis. The design will a ssure that flows delivered to Type 5 stream reaches w ill approximate, but in no case exceed, durations ranging from 50% of the 2-year to the 50-year peak flow. o Flow splitting devices or drainage BMP’s that deliver flow to category IV wetlands will also be designed us ing continuous hydrologic modeling to preserve pre-project wetla nd hydrologic conditions unless specifically waived or exempted by regulatory agencies with permitting jurisdiction; and • The project site must be drai ned by a conveyance system that is comprised entirely of manmade conveyance elements (e.g., pipes, ditches, outfall protection, etc.) and extends to the ordinary high water line of the exempt receiving water; and • The conveyance system between the project si te and the exempt receiving water shall have sufficient hydraulic cap acity to convey discharges from future build-out conditions (under current zoning) of the site, and the existing condition from non-project areas from which runoff is or will be collected; and • Any erodible elements of the manmade c onveyance system must be adequately stabilized to prevent erosion under the conditions noted above. If the discharge is to a stream that leads to a wetland, or to a wetland that has an outflow to a stream, both this minimum requirement (Minimum Requirement #7) and Minimum Requirement #8 apply. Permittees may petition Ecology to exempt proj ects in additional areas . A petition must justify the proposed exemption based upon a hydr ologic analysis that demonstrates that the potential stormwater runoff from the exem pted area will not significantly increase the Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 26 of 30 erosion forces on the stream channel nor have near-field impacts (see Section 7 of this Appendix). Thresholds The following require construction of flow c ontrol facilities and/or land use management BMPs that will achieve the standard flow control requirement for western Washington (see Table 4.2): • Projects in which the total of effective impervious surfaces is 10,000 square feet or more in a threshold discharge area, or • Projects that convert ¾ acres or more of native vegetation to lawn or landscape, or convert 2.5 acres or more of native vegetation to pasture in a threshold discharge area, and from which there is a surface discharg e in a natural or man-made conveyance system from the site, or • Projects that through a combination of ef fective impervious surfaces and converted pervious surfaces cause a 0.1 cubic feet pe r second increase in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model. That portion of any development project in which the above thresholds are not exceeded in a threshold discharge ar ea shall apply Onsite Stormwater Management BMPs in accordance with Minimum Requirement #5. Standard Flow Control Requirement Stormwater discharges shall match devel oped discharge durations to pre-developed durations for the range of pre-developed disc harge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. Th e pre-developed condition to be matched shall be a forested land cover unless: • Reasonable, historic information is available that indicates the site was prairie prior to settlement (modeled as “pasture” in the Western Washington Hydrology Model); or Table 4.2 Flow Control Requirements by Threshold Discharge Area Flow Control Facilities On-site Stormwater Management BMPs < ¾ acres conversion to lawn/landscape, or < 2.5 acres to pasture a > ¾ acres conversion to lawn/landscape, or > 2.5 acres to pasture a a < 10,000 square f eet of effective impervious area a > 10,000 square f eet of effective impervious area a a > 0.1 cubic feet per second increase in the 100-year flood frequency a a Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 27 of 30 • The drainage area of the immediate stream and all subsequent downstream basins have had at least 40% total impervious area since 1985. In this case, the pre-developed condition to be matched shall be the existing land cover condition. Where basin-specific studies determine a stream channel to be unstable, even though the above criterion is met, the pre-developed c ondition assumption shall be the “historic” land cover condition, or a land cover condition commensurate with achieving a target flow regime identified by an approved basin study. This standard requirement is waived for site s that will reliably in filtrate all the runoff from impervious surfaces and converted pervious surfaces. Western Washington Alternative Requirement An alternative requirement may be establis hed through application of watershed-scale hydrological modeling and supporting field obs ervations. Possible reasons for an alternative flow control requirement include: • Establishment of a stream–specific thres hold of significant bedload movement other than the assumed 50% of the 2-year peak flow; • Zoning and Land Clearing Ordinance restric tions that, in combination with an alternative flow control standard, maintain or reduce the natura lly occurring erosive forces on the stream channel; or • A duration control standard is not nece ssary for protection, maintenance, or restoration of designated beneficial uses or Clean Water Act compliance. See Section 7 Basin/Watershed Planning of th is Appendix for details on how alternative flow control requirements may be established. Additional Requirement Flow Control BMPs shall be selected, de signed, and maintained in accordance with Volume III of the Stormwater Management Manual for Western Washington (2005) or an approved equivalent. 4.8 Minimum Requirement #8: Wetlands Protection Applicability The requirements below apply only to projec ts whose stormwater discharges into a wetland, either directly or i ndirectly through a conveyance sy stem. These requirements must be met in addition to meeting Mi nimum Requirement #6, Runoff Treatment. Thresholds The thresholds identified in Minimu m Requirement #6 – Runoff Treatment, and Minimum Requirement #7 – Flow Control shal l also be applied for discharges to wetlands. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 28 of 30 Standard Requirement Discharges to wetlands shall maintain th e hydrologic conditions, hydrophytic vegetation, and substrate characteristics necessary to support existing and designated uses. The hydrologic analysis shall use the existing la nd cover condition to de termine the existing hydrologic conditions unless directed otherwise by a regulatory agency with jurisdiction. A wetland can be considered for hydrologic mo dification and/or stormwater treatment in accordance with Guide Sheet 1B in Appendix I-D on the Stormwater Management Manual for Western Washington (2005). Additional Requirements Stormwater treatment and flow control faci lities shall not be built within a natural vegetated buffer, except for: • necessary conveyance systems as approved by the Permittee; or • as allowed in wetlands approved for hydrol ogic modification and/or treatment in accordance with Guidesheet 1B in Appendix I-D of the Stormwater Management Manual for Western Washington (2005). An adopted and implemented basin plan prep ared in accordance with the provisions of Section 7 of this Appendix may be used to develop requirements for wetlands that are tailored to a specific basin. 4.9 Minimum Requirement #9: Operation and Maintenance Permittees must require an ope ration and maintenance manual that is consistent with the provisions in Volume V of the Stormwater Management Manual for Western Washington (2005) for all proposed stormwater faciliti es and BMPs. The party (or parties) responsible for maintenance and operation sh all be identified in the operation and maintenance manual. For private facilitie s approved by the Permittee, a copy of the manual shall be retained onsite or within r easonable access to the site, and shall be transferred with the property to the new ow ner. For public facilities, a copy of the manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection by the local government. Section 5. Adjustments Adjustments to the Minimum Requirements may be granted by the Permittee provided that a written finding of fact is prepar ed, that addresses the following: • The adjustment provides substantiall y equivalent environmental protection. • Based on sound Engineering practices, the objectives of safety, function, environmental protection and facility maintenance, are met. Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 29 of 30 Section 6. Exceptions/Variances Exceptions/variances (exceptions) to the Mi nimum Requirements may be granted by the Permittee following legal public notice of an app lication for an exception or variance, legal public notice of the Permittee’s decision on the a pplication, and written findings of fact that documents the Permittees determination to grant an exception. Permittees shall keep records, including the written findings of fact, of all local exceptions to the Minimum Requirements. Project-specific design exceptions based on site-specific conditions do not require prior approval of the Department. The Permittee must seek prior approval by the Department for any jurisdiction-wide exception. The Permittee may grant an exception to the mini mum requirements if such application imposes a severe and unexpected economic hardship. To determine whether the application imposes a severe and unexpected economic hardship on the project applicant, the Permittee must consider and document with written findi ngs of fact the following: • The current (pre-project) use of the site, and • How the application of the minimum requi rement(s) restricts the proposed use of the site compared to the re strictions that existed pr ior to the adoption of the minimum requirements; and • The possible remaining uses of the site if the exception were not granted; and • The uses of the site that would have b een allowed prior to the adoption of the minimum requirements; and • A comparison of the estimated amount and pe rcentage of value lo ss as a result of the minimum requirements versus the esti mated amount and percentage of value loss as a result of requirements that ex isted prior to adoption of the minimum requirements; and • The feasibility for the owner to alter the project to apply the minimum requirements. In addition any exception must meet the following criteria: • The exception will not increase risk to the public health and welfare, nor injurious to other properties in the vicinity and/or downstream, a nd to the quality of waters of the state; and • The exception is the least possible exception that could be granted to comply with the intent of the Minimum Requirements. Section 7. Basin/Watershed Planning Basin/Watershed planning may be used by th e Permittee to tailor Minimum Requirement #6 Runoff Treatment, Minimum Requi rement #7 Flow Control, a nd/or Minimum Requirement #8 Western Washington Phase II M unicipal Stormwater Permit January 17, 2007 Appendix 1 - Minimum Technical Requirements Page 30 of 30 Wetlands Protection. Basin planning may be used to support alterna tive treatment, flow control, and/or wetland protection requireme nts to those contained in Secti on 4 of this Appendix. Basin planning may also be used to demonstrate an equi valent level of treatment , flow control, and/or wetland protection through the construction and use of regional stormwater facilities. Basin planning provides a mechanism by which the minimum requirements and implementing BMP’s can be evaluated and refi ned based on an analysis of a basin or watershed. Basin plans are may be used to develop control strategies to address impacts from future development and to correct specific problems whose s ources are known or suspected. Ba sin plans can be effective at addressing both long-term cumulative impacts of po llutant loads and short-term acute impacts of pollutant concentrations, as well as hydrologic impacts to streams, wetlands, and ground water resources. Basin planning will require the use of computer m odels and field work to verify and support the models. The USGS has develope d software called “GenScn” (Gen eration and Analysis of Model Simulation Scenarios) that can facilitate basin planning. The program is a Windows-based application of HSPF that predicts water quality and quantity changes for multiple scenarios of land use and water management within a basin. Permittees who are co nsidering the use of basin/watershed plans to modify or tailor on e or more of the minimum requirements are encouraged to contact Ecology ea rly in the planning stage. Some examples of how Basin Planning can al ter the minimum requirements are given in Appendix I-A from the Stormwater Management Manual for Western Washington (2005). In order for a basin plan to serve as a means of modifyi ng the minimum requirements the following conditions must be met: • The plan must be formally adopted by a ll jurisdictions with responsibilities under the plan; and • All ordinances or regulations called fo r by the plan must be in effect; and • The basin plan must be reviewed and approved by Ecology.