HomeMy WebLinkAbout07-19-2017 HEARING EXAMINER AGENDAHEARING EXAMINER
July 19, 2017
5:30 p.m.
City Council Chambers
25 West Main Street
I.Case No:VAR17-0005 – Janet Holt
Applicant(s)
Property Owner:Janet Holt
Request: Request for a variance to decrease the rear yard setback
from the previously established minimum 5 feet to 0 feet to
expand the existing second-story deck to the property line
within the R5, Residential zoning district.
Project Location: 10511 SE 302nd St, Auburn, WA 98092
Parcel Number(s): 165730-0420 (King County)
Page 1 of 94
Exhibit 1
Page 2 of 94
Page 3 of 94
Page 4 of 94
Page 5 of 94
Page 6 of 94
Page 7 of 94
Page 8 of 94
Page 9 of 94
Page 10 of 94
Page 11 of 94
Page 12 of 94
Exhibit 2
Page 13 of 94
Page 14 of 94
Page 15 of 94
Page 16 of 94
Page 17 of 94
Exhibit 3
Page 18 of 94
Page 19 of 94
Exhibit 4
Page 20 of 94
Exhibit 5Page 21 of 94
Exhibit 6Page 22 of 94
VAR 17-0005
Exhibit 7 – Aerial Image 2015
Obtained from Mapping tool on July 6, 2017.
Page 23 of 94
Exhibit 8
Page 24 of 94
Page 25 of 94
Page 26 of 94
Page 27 of 94
Page 28 of 94
Exhibit 9 – Site Visit Pictures taken May 22, 2017 by Staff
Picture No. 1: Proposed deck expansion area. Picture taken from the South-West corner looking North.
Picture No.2: Proposed deck expansion area. Picture taken from the South-West corner looking North-
East.
Exhibit 9
Page 29 of 94
Picture No. 3: Side yard area located on the East side of the property. Picture taken from the North-East
Corner looking South. This picture illustrates the slope along the East side of the property.
Picture No. 4: South-East corner of property.
Picture taken from the South-West area of the
property.
Page 30 of 94
Picture No. 5: West side yard. Picture taken from the South-West corner of the house looking north.
Picture No. 6: Westside of house. Picture taken
from the South-West corner of the house
looking North.
Page 31 of 94
Exhibit 10
Page 32 of 94
Exhibit 11
Page 33 of 94
Page 34 of 94
Page 35 of 94
Page 36 of 94
Exhibit 12
Page 37 of 94
Page 38 of 94
Page 39 of 94
Page 40 of 94
Page 41 of 94
Page 42 of 94
Page 43 of 94
Page 44 of 94
Page 45 of 94
Page 46 of 94
Page 47 of 94
Page 48 of 94
Page 49 of 94
Page 50 of 94
King County Department of Assessments: eReal Property
ADVERTISEMENT
I Ntw Sl'arch Properly Ta.x Bill 1\lnp This Proptrly I GloSSlll)' or Terms 11 An•;t Report I l'rint Properly Dcrnil m
Residential Area Property Name Legal Description
I COBBLE CREEK Plat Block: Plat Lot: 42
Highest & Best Use As If Vacant Highest & Best Use As Improved Present Use Land SqFt Acres
Rainier Territorial Olympics Cascades Seattle Skyline Puget Sound Lake Washington Lake Sammamish Lake/River/Creek Other View
Historic Site Current Use Nbr Bldg Sites Adjacent to Golf Fairway Adjacent to Greenbelt Other Designation Deed Restrictions Development Rights Purchased Easements
062-009 (SW Appraisal District)
SINGLE FAMILY
PRESENT USE Single Family(Res Use/Zone) 9,750 0.22
Views
Designations
(none)
NO NO NO NO NO NO Native Growth Protection NO �as.e111ea• DNR Lease NO
PARCEL DATA Jurisdiction AUBURN Levy Code 0133 Property Type R Plat Block / Building Number Plat Lot I Unit Number 42 Quarter-Section-Township-SW-5 -21-5 Range
LAND DATA
Percentage Unusable 0 Unbuildable NO Restrictive Size Shape NO Zoning RS Water WATER DISTRICT Sewer!Septic PUBLIC Road Access PUBLIC Parking Street Surface PAVED Waterfront Waterfront Location Waterfront Footage 0 Lot Depth Factor 0 Waterfront Bank Tide/Shore Waterfront Restricted Access Waterfront Access Rights NO Poor Quality NO Proximity Influence NO
Nuisances Topography Traffic Noise Airport Noise Power Lines NO Other Nuisances NO Problems Water Problems NO Transportation Concurrency NO Other Problems NO Environmental
environmental Yl:S
Environmental I Information Type Source Delineation I Percentage Istudy Affected LandslideHazardj JURISDICTION N lo I
BUILDING Building Number 1 g Click the camera to see more pictures. Year Bui lt 1988 Year Renovated 0 Stories 1 Living Units 1 Grade 9 Better
http:/ /b 1 ue.kingcounty. com/ Assessor/ eRealProperty /Detail. aspx?ParcelNbr= 165 73 004 2 0
Page 1 of 3
ADVERTISI
6/30/2017
Exhibit 13
Page 51 of 94
Page 52 of 94
Page 53 of 94
Page 54 of 94
Exhibit 14
Page 55 of 94
Page 56 of 94
Page 57 of 94
Page 58 of 94
King County Code – Title 21 – Zoning
http://www.kingcounty.gov/council/legislation/kc_code/24_30_Title_21A.aspx
21A.12.030 Densities and dimensions - residential and rural zones.
A.Densities and dimensions - residential and rural zones.
RURAL RESIDENTIAL
ZONE
S
RURAL AREA URBA
N
RE-
SERV
E
RESIDENTIAL
STANDARD
S
RA-
2.5
RA-5 RA-
10
RA-
20
UR R-1
(17)
R-4 R-6 R-8 R-12 R-18 R-24 R-48
Base
Density:
Dwelling
Unit/Acre
(15) (28)
0.2
du/a
c
0.2
du/a
c
0.1
du/a
c
0.05
du/a
c
0.2
du/ac
(21)
1
du/
ac
4
du/
ac
(6)
6
du/a
c
8
du/a
c
12
du/a
c
18
du/a
c
24
du/a
c
48
du/a
c
Maximum
Density:
Dwelling
Unit/Acre
(1)
0.4
du/a
c
(20)
6
du/
ac
(22)
8
du/
ac
(27)
9
du/a
c
12
du/a
c
(27)
12
du/a
c
16
du/a
c
(27)
18
du/a
c
24
du/a
c
(27)
27
du/a
c
36
du/a
c
(27)
36
du/a
c
48
du/a
c
(27)
72
du/a
c
96
du/a
c
(27)
Minimum
Density:
(2)
85
%
(12)
(18)
(23)
85%
(12)
(18)
85%
(12)
(18)
80%
(18)
75%
(18)
70%
(18)
65%
(18)
Minimum
Lot Area
(13)
1.87
5 ac
3.75
ac
7.5
ac
15
ac
Minimum
Lot
Width
(3)
135
ft
135
ft
135
ft
135
ft
35 ft
(7)
35
ft
(7)
30
ft
30 ft 30 ft 30 ft 30ft 30 ft 30 ft
Minimum
Street
Setback
(3)
30 ft
(9)
30 ft
(9)
30ft
(9)
30 ft
(9)
30 ft
(7)
20
ft
(7)
10
ft
(8)
10 ft
(8)
10 ft
(8)
10 ft
(8)
10 ft
(8)
10ft
(8)
10 ft
(8)
Minimum
Interior
Setback
(3) (16)
5 ft
(9)
10ft
(9)
10 ft
(9)
10 ft
(9)
5 ft
(7)
5 ft
(7)
5 ft 5 ft 5 ft 5 ft
(10)
5 ft
(10)
5 ft
(10)
5 ft
(10)
Base Height
(4)
40 ft 40 ft 40 ft 40 ft 35 ft 35
ft
35
ft
(25)
35 ft
45 ft
(14)
(25)
35 ft
45 ft
(14)
(25)
60 ft 60 ft
80 ft
(14)
60 ft
80 ft
(14)
60 ft
80 ft
(14)
Maximum
Impervious
Surface:
Percentage
(5)
25%
(11)
(19)
(26)
20%
(11)
(19)
(26)
15%
(11)
(19)
(24)
(26)
12.5
%
(11)
(19)
(26)
30%
(11)
(26)
30
%
(11)
(26)
55
%
(26)
70%
(26)
75%
(26)
85%
(26)
85%
(26)
85%
(26)
90%
(26)
B.Development conditions.
1.This maximum density may be achieved only through the application of
residential density incentives in accordance with K.C.C. chapter 21A.34 or transfers of
development rights in accordance with K.C.C. chapter 21A.37, or any combination o f
density incentive or density transfer.
Exhibit 15
Page 59 of 94
2. Also see K.C.C. 21A.12.060.
3. These standards may be modified under the provisions for zero -lot-line and
townhouse developments.
4. Height limits may be increased if portions of the structure that exceed the
base height limit provide one additional foot of street and interior setback for each foot
above the base height limit, but the maximum height may not exceed seventy -five
feet. Netting or fencing and support structures for the netting or fencing used to contain
golf balls in the operation of golf courses or golf driving ranges are exempt from the
additional interior setback requirements but the maximum height shall not exceed
seventy-five feet, except for recreation or multiuse parks, where the maximum height shall
not exceed one hundred twenty-five feet, unless a golf ball trajectory study requires a
higher fence.
5. Applies to each individual lot. Impervious surface area standards for:
a. Regional uses shall be established at the time of permit review;
b. Nonresidential uses in rural area and residential zones shall comply with
K.C.C. 21A.12.120 and 21A.12.220;
c. Individual lots in the R-4 through R-6 zones that are less than nine thousand
seventy-six square feet in area shall be subject to the applicable provisions of the nearest
comparable R-6 or R-8 zone; and
d. A lot may be increased beyond the total amount permitted in this chap ter
subject to approval of a conditional use permit.
6. Mobile home parks shall be allowed a base density of six dwelling units per
acre.
7. The standards of the R-4 zone apply if a lot is less than fifteen thousand
square feet in area.
8. At least twenty linear feet of driveway shall be provided between any garage,
carport or other fenced parking area and the street property line. The linear distance shall
be measured along the center line of the driveway from the access point to such garage,
carport or fenced area to the street property line.
9.a. Residences shall have a setback of at least one hundred feet from any
property line adjoining A, M or F zones or existing extractive operations. However,
residences on lots less than one hundred fifty feet in width adjoining A, M or F zones or
existing extractive operations shall have a setback from the rear property line equal to
fifty percent of the lot width and a setback from the side property equal to twenty -five
percent of the lot width.
b. Except for residences along a property line adjoining A, M or F zones or
existing extractive operations, lots between one acre and two and one -half acres in size
shall conform to the requirements of the R-1 zone and lots under one acre shall conform
to the requirements of the R-4 zone.
10.a. For developments consisting of three or more single-detached dwellings
located on a single parcel, the setback shall be ten feet along any property line abutting
R-1 through R-8, RA and UR zones, except for structures in on-site play areas required
in K.C.C. 21A.14.190, which shall have a setback of five feet.
b. For townhouse and apartment development, the setback shall be twenty
feet along any property line abutting R-1 through R-8, RA and UR zones, except for
structures in on-site play areas required in K.C.C. 21A.14.190, which shall have a setback
Page 60 of 94
of five feet, unless the townhouse or apartment development is adjacent to property upon
which an existing townhouse or apartment development is located.
11. Lots smaller than one-half acre in area shall comply with standards of the
nearest comparable R-4 through R-8 zone. For lots that are one-half acre in area or
larger, the maximum impervious surface area allowed shall be at least ten thousand
square feet. On any lot over one acre in area, an additional five percent of the lot area
may be used for buildings related to agricultural or forestry practices. For lots smaller than
two acres but larger than one-half acre, an additional ten percent of the lot area may be
used for structures that are determined to be medically necessary, if the applicant submits
with the permit application a notarized affidavit, conforming with K.C.C. 21A.32.170A.2.
12. For purposes of calculating minimum density, the applicant may request that
the minimum density factor be modified based upon the weighted average slope of the
net buildable area of the site in accordance with K.C.C. 21A.12.087.
13. The minimum lot area does not apply to lot clustering proposals as provided
in K.C.C. chapter 21A.14.
14. The base height to be used only for projects as follows:
a. in R-6 and R-8 zones, a building with a footprint built on slopes exceeding a
fifteen percent finished grade; and
b. in R-18, R-24 and R-48 zones using residential density incentives and
transfer of density credits in accordance with this title.
15. Density applies only to dwelling units and not to sleeping units.
16. Vehicle access points from garages, carports or fenced parking areas shall
be set back from the property line on which a joint use driveway is located to provide a
straight line length of at least twenty-six feet as measured from the center line of the
garage, carport or fenced parking area, from the access point to the opposite side of the
joint use driveway.
17.a. All subdivisions and short subdivisions in the R-1 zone shall be required
to be clustered if the property is located within or contains:
(1) a floodplain;
(2) a critical aquifer recharge area;
(3) a regionally or locally significant resource area;
(4) existing or planned public parks or trails, or connections to such facilities;
(5) a category type S or F aquatic area or category I or II wetland;
(6) a steep slope; or
(7) an urban separator or wildlife habitat network designated by the
Comprehensive Plan or a community plan.
b. The development shall be clustered away from critical areas or the axis of
designated corridors such as urban separators or the wildlife habitat network to the extent
possible and the open space shall be placed in a separate tract that includes at least fifty
percent of the site. Open space tracts shall be permanent and shall be dedicated to a
homeowner's association or other suitable organization, as determined by the director,
and meet the requirements in K.C.C. 21A.14.040. On-site critical area and buffers and
designated urban separators shall be placed within the open space tract to the extent
possible. Passive recreation, with no development of recreational facilities, and natural -
surface pedestrian and equestrian trails are acceptable uses within the open space tract.
18. See K.C.C. 21A.12.085.
Page 61 of 94
19. All subdivisions and short subdivisions in R-1 and RA zones within the North
Fork and Upper Issaquah Creek subbasins of the Issaquah Creek Basin (the North Fork
and Upper Issaquah Creek subbasins are identified in the Issaquah Creek Basin and
Nonpoint Action Plan) and the portion of the Grand Ridge subarea of the East
Sammamish Community Planning Area that drains to Patterson Creek shall have a
maximum impervious surface area of eight percent of the gross acreage of the
plat. Distribution of the allowable impervious area among the platted lots shall be
recorded on the face of the plat. Impervious surface of roads need not be counted
towards the allowable impervious area. Where both lot- and plat-specific impervious
limits apply, the more restrictive shall be required.
20. This density may only be achieved on RA 2.5 zoned parcels receiving
density from rural forest focus areas through a transfer of density credit pursuant to K.C.C.
chapter 21A.37.
21. Base density may be exceeded, if the property is located in a designated
rural city urban growth area and each proposed lot contains an occupied legal residence
that predates 1959.
22. The maximum density is four dwelling units per acre for properties zoned R -
4 when located in the Rural Town of Fall City.
23. The minimum density requirement does not apply to properties located
within the Rural Town of Fall City.
24. The impervious surface standards for the county fairground facility are
established in the King County Fairgrounds Site Development Plan, Attachment A to
Ordinance 14808* on file at the department of natural resources and parks and the
department of permitting and environmental review. Modifications to that standard may
be allowed provided the square footage does not exceed the approved impervious
surface square footage established in the King County Fairgrounds Site Development
Plan Environmental Checklist, dated September 21, 1999, Attachment B to Ordinance
14808*, by more than ten percent.
25. For cottage housing developments only:
a. The base height is eighteen feet.
b. Buildings have pitched roofs with a minimum slope of six and twelve may
extend up to twenty-five feet at the ridge of the roof.
26. Impervious surface does not include access easements serving neighboring
property and driveways to the extent that they extend beyond the street setback due to
location within an access panhandle or due to the application of King County Code
requirements to locate features over which the applicant does not have control.
27. Only in accordance with K.C.C. 21A.34.040.F.1.g. and F.6.
28. On a site zoned RA with a building listed on the national register of historic
places, additional dwelling units in excess of the maximum density may be allowed
under K.C.C. 21A.12.042. (Ord. 17841 § 31, 2014: Ord. 17539 § 33, 2013: Ord.
17420 § 99, 2012: Ord. 16267 § 25, 2008: Ord. 15245 § 6, 2005: Ord. 15051 § 126,
2004: Ord. 15032 § 17, 2004: Ord. 14808 § 4, 2003: Ord. 14807 § 7, 2003: Ord.
14429 § 2, 2002: Ord. 14190 § 33, 2001: Ord. 14045 § 18, 2001: Ord. 13881 § 1, 2000:
Ord. 13571 § 1, 1999: Ord. 13527 § 1, 1999: Ord. 13274 § 10, 1998: Ord. 13086 § 1,
1998: Ord. 13022 § 16, 1998: Ord. 12822 § 6, 1997: Ord. 12549 § 1, 1996: Ord. 12523
§ 3, 1996: Ord. 12320 § 2, 1996: Ord. 11978 § 4, 1995: Ord. 11886 § 5, 1995: Ord.
Page 62 of 94
11821 § 2, 1995: Ord. 11802 § 3, 1995: Ord. 11798 § 1, 1995: Ord. 11621 § 41, 1994:
Ord. 11555 § 5, 1994: Ord. 11157 § 15, 1993: Ord. 10870 § 340, 1993).
*Available in the King County Archives.
Page 63 of 94
Exhibit 16
Page 64 of 94
Page 65 of 94
Page 66 of 94
Exhibit 16
Page 67 of 94
Page 68 of 94
Page 69 of 94
Exhibit 17
Page 70 of 94
Exhibit 18
Page 71 of 94
Page 72 of 94
Guidelines for Erosion Control Practices
As required by Ecology, this SWPPP must contain the 13 required elements. Check off each element as it is
addressed in the SWPPP Short Form and/or on your site plan.
___ 1. Mark Clearing Limits (orange construction fence, staking with ribbon).
___ 2. Establish Construction Access (gravel entrance, tire wash area).
___ 3. Control Flow Rates (using pipe, drainage swales, berms).
___ 4. Install Sediment Controls (silt fence, sediment traps).
___ 5. Stabilize Soils (mulch, hydroseed, straw).
___ 6. Protect Slopes (divert water from top of slope, cover with plastic or erosion
control blanket).
___ 7. Protect Drain Inlets (catch basin inserts).
___ 8. Stabilize Channels and Outlets (cover with grass, riprap).
___ 9. Control Pollutants (maintain equipment to prevent leaks).
___ 10. Control Dewatering (pump to sediment trap).
___ 11. Maintain BMPs (weekly maintenance/replacement, preparation for storm events).
___ 12. Manage the Project (establish construction schedule, phasing, contact numbers).
___ 13. Protect Low Impact Development BMPs (avoid compaction and/or sedimentation of
bioretention areas, if applicable).
Several common erosion control techniques are explained and described in this section. Standard details for
installation of these methods are included in this document. The applicant does not need to reproduce these
drawings, but must indicate where each BMP will be used on a site plan and indicate which detail will be used.
An example site plan and symbols list is provided to assist the applicant in preparation of their own site plan.
Only those erosion and sediment control techniques most pertinent to small construction sites are included
here. More detailed information on construction BMPs can be found in Volume II of the Department of
Ecology (Ecology) Stormwater Management Manual for Western Washington (SWMMWW). The BMP
numbers referenced are BMPs located in the SWMMWW.
For phased construction plans, clearly indicate erosion control methods to be used for each phase of
construction.
1.Mark Clearing Limits
All construction projects must clearly mark any clearing limits, sensitive areas and their buffers, and any trees
that will be preserved prior to beginning any land disturbing activities, including clearing and grading. Clearly
mark limits both in the field and on the plans. Do not staple or wire fences to trees.
Applicable BMPs include:
BMP C101: Preserving Natural Vegetation
BMP C102: Buffer Zones
BMP C103: High Visibility Fence
Exhibit 19
Page 73 of 94
2. Establish Construction Access
All construction projects subject to vehicular traffic shall provide a means of preventing vehicle “tracking” of
soil from the site onto City streets. At a minimum, there shall be a rock pad construction entrance at every
construction access point. Note: The applicant should consider placing the entrance in the area for future
driveway(s), as the rock can be used for driveway base material. The entrance(s) shall be inspected weekly and
if excessive sediment is found, more rock shall be added to ensure proper functioning. See Figure C- 2
Establish Construction Access-Construction Entrance.
If sediment is tracked off site, it shall be swept or shoveled from the paved surface on a daily basis. Washing of
the streets to remove the sediment is not permitted because wash water can transport sediments to streams
and other water courses via the City storm drainage system.
The entrance must be identified on the site plan and must conform to Figure C- 2.
Applicable BMPs include:
BMP C105: Stabilized Construction Entrance
BMP C106: Wheel Wash
BMP C107: Construction Road/Parking Area Stabilization
3. Control Flow Rates
Flow control BMPs must be used to protect properties and waterways downstream of construction sites
from erosion and the associated discharge of turbid waters. Construct stormwater retention or
detention facilities as one of the first steps in grading. Protect permanent infiltration ponds from
siltation when these facilities are used for flow control during construction.
A combination of drainage swales and possibly a sediment trap may be used to control runoff and trap
associated sediment before it leaves the construction site.
A. Sediment traps
Refer to BMP C240: Sediment Trap and Figure C- 3 Control Flow Rates/Install Sediment Controls -
Sediment Trap Cross-Section & Outlet (SWMMWW Vol II, pg. 104).
Sediment traps are small temporary ponds (typically less than 3 feet deep) used to trap sediment
suspended in site runoff before it leaves a construction site. As concentrated surface water pools
within the pond, sediment is allowed to settle out of the water. Typically, a sediment trap will not be
required for small sites as long as concentrated stormwater runoff (swales or ditches) does not occur.
Use Table C- 1 Sediment Trap Sizing below for sizing your sediment trap.
Contributing Area (Acres) Required Surface Area of Pond (sq.
ft.)
1/8 acre or less 130
¼ acre or less 260
½ acre or less 520
¾ acre or less 780
1 acre or less 1040
Page 74 of 94
Table C- 1 Sediment Trap Sizing
If expected time of construction or downstream conditions warrant more protection, see BMP C240
for sizing information.
NOTE: If dewatering or significant stormwater runoff is expected, a sediment trap should be used to
settle out solids before discharging to the City system.
Page 75 of 94
B. Drainage Swales
Drainage swales are temporary ditches (minimum slope of 0.5% and a maximum of 10%) used to
convey concentrated stormwater flows away from construction activities into a temporary sediment
trap. Drainage swales carrying concentrated flows must discharge into a sediment trap or pond.
Swales should be stabilized with erosion protection. See Figure C- 4 Control Flow Rates-Drainage
Swale Cross-Sections (SWMMWW Vol II, pg. 4-62). Note: Swales should be completely stabilized
before directing concentrated flows or they will erode.
Applicable BMPs include:
BMP C203: Water Bars
BMP C207: Check Dams
BMP C209: Outlet Protection
BMP C235: Wattles
BMP C240: Sediment Trap
BMP C241: Temporary Sediment Pond
4. Install Sediment Controls
Sediment barriers should be used downslope of disturbed areas. Sediment barriers are intended to create a
barrier to slow the “sheet” flow of stormwater and allow the sediment to settle out behind the barrier. Do not
use sediment barriers in streams, channels, ditches or around inlets/outlets of culverts. Sediment barriers
selected shall be identified on the site plan and must conform to the BMPs and/or City of Auburn Standard
Details outlined below.
A. Silt fence
A silt fence is a temporary sediment barrier consisting of filter fabric, attached to supporting posts and
entrenched into the soil. See Figure C- 5 Install Sediment Controls-Silt Fence.
B. Berm Barriers
A continuous berm is a temporary diversion dike or sediment barrier. It may be constructed with:
Wattles. See Figure C- 6 Install Sediment Controls-Straw Wattle Rolls (SWMMWW Vol II,
pg. 4-98).
Soil, sand, or aggregate encased within a geosynthetic fabric.
Sand bags.
Applicable BMPs include:
BMP C208 Triangular Silt Dike (TSD) (Geotextile Encased Check Dam)
BMP C231: Brush Barrier
BMP C232: Gravel Filter Berm
BMP C233: Silt Fence
BMP C234: Vegetated Strip
BMP C235: Wattles
Page 76 of 94
5. Stabilize Soils
Soil erosion protection is applied over the soil surface to reduce erosion from rainfall and wind. It can also be
used to aid the establishment of vegetation. Between October 1st and April 30th, no soils shall remain exposed
for more than 2 days unless they are being actively worked. From April 1st to September 30th, no soils shall
remain exposed for more than 7 days unless they are being actively worked. Implement soil erosion protection
in the following ways:
A. Mulches/Seeding/Hydroseeding
Mulching is the application of a protective layer of straw or other suitable material to the soil surface.
Mulch can be applied to any site where soil has been disturbed and the protective vegetation has
been removed. An approved Hydroseed mix for erosion control is provided in Table C- 2 Temporary
Erosion Control Seed Mix below. Standards and guidelines for mulch are provided in Table C- 3
Mulch Standards and Guidelines below. Materials that may be used for mulching include:
Straw or hay
Compost material
Wood or bark chips
Hydraulically applied grass seed (Hydroseed)
Bonded Fiber Matrix
Applicable BMPs include:
BMP C121: Mulching
BMP C120: Temporary and Permanent Seeding
BMP C124: Sodding
BMP C125: Compost
BMP C126: Topsoiling
BMP C130: Surface Roughening
BMP C140: Dust Control
% Weight % Purity % Germination
Chewings or annual bluegrass
Festuca rubra var. commutate or Poa anna 40 98 90
Perennial rye
Lolium perenne 50 98 90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis 5 92 85
White Dutch clover
Trifolium repens 5 98 90
Table C- 2 Temporary Erosion Control Seed Mix
Page 77 of 94
Mulch
Material
Quality
Standards
Application
Rates
Remarks
Straw Air-dried; free
from undesirable seed
and coarse material.
3” thick; 5
bales per 1000
sf or 2 to 3 tons
per acre.
Cost-effective protection when applied with adequate
thickness. Hand-application generally requires greater thickness
than blown straw. The thickness of straw may be reduced by half
when used in conjunction with seeding. In windy areas, straw must
be held in place by crimping, using a tackifier, or covering with
netting. Blown straw always has to be held in place with a tackifier
as even light winds will blow it away. Straw, however, has several
deficiencies that should be considered when selecting mulch
materials. If often introduces and/or encourages the propagation of
weed species and it has no significant long-term benefits. Straw
should be used only if mulches with long-term benefits are
unavailable locally. It should also not be used within the ordinary
high-water elevation of surface waters (due to flotation).
Hydro-
mulch
No growth
inhibiting factors.
Approx. 25-
30 lbs per 1000
sf or 1500-2000
lbs per acre.
Shall be applied with hydromulcher. Shall not be used without
seed and tackifier unless the application rate is at least doubled.
Fivers longer than about ¾ - 1 inch clog hydromulch equipment.
Fibers should be kept to less than ¾ inch.
Compos
ted Mulch
and Compost
No visible water or
dust during handling.
Must be purchased
from supplier with a
Solid Waste Handling
permit (unless exempt)
3” thick,
min.; approx.
100 tons per
acre (approx.
800 lbs. per
yard).
More effective control can be obtained by increasing thickness
to 3”. Excellent mulch for protecting final grades until landscaping
because it can be directly seeded or tilled into soil as an
amendment. Composted mulch has a coarser size gradation than
compost. It is more stable and practical to use in wet areas and
during rainy weather conditions.
Chipped
Site
Vegetation
Average size shall
be several inches.
Gradations from fine to
6-inches in length for
texture, variation, and
interlocking properties.
3”
minimum
thickness
This is a cost-effective way to dispose of debris from clearing
and grubbing, and it eliminates the problems associated with
burning. Generally, it should not be used on slopes above approx.
10% because of its tendency to be transported by runoff. It is not
recommended within 200 feet of surface waters. If seeding is
expected shortly after mulch, the decomposition of the chipped
vegetation may tie up nutrients important to grass establishment.
Table C- 3 Mulch Standards and Guidelines
B. Erosion Control Blankets/ Mats
Erosion control blankets are suited for post-construction site stabilization, but may be used for
temporary stabilization of highly erosive soils. Erosion control blankets are suitable for steep slopes,
stream banks, and areas where vegetation will be slow to establish. These blankets are typically made
from straw, coconut fiber, excelsior, or synthetic material that is enveloped in plastic, biodegradable
netting, jute, polypropylene, or nylon. See Figure C- 7 Protect Slopes – Erosion Blankets and Turf
Reinforcement Mats (SWMMWW Vol II, pg. 4-25).
Applicable BMPs include:
BMP C122: Nets and Blankets
C. Gravel/Riprap
Gravel and Riprap are used to protect hillsides, drainage channels, stream banks, and pipe outlets
from erosion due to surface water flow.
Page 78 of 94
D. Plastic Sheeting
Plastic sheeting is a temporary method of erosion control. Plastic covering provides immediate, short-
term erosion protection to slopes, soil stockpiles, and other disturbed areas. Unlike the other erosion
protection techniques mentioned above, plastic sheeting shall be removed prior to applying
permanent erosion protection. See Figure C- 8 Tarp Covering.
Applicable BMPs include:
BMP C123: Plastic Covering
6. Protect Slopes
Design, construct and phase projects in a manner that will minimize erosion. Protect slopes by diverting water
at the top of the slope. Reduce slope velocities by minimizing the continuous length of slope. This can be
accomplished by terracing and roughening slope sides. Seeding and establishing vegetation on slopes will help
protect slopes as well.
Applicable BMPs include:
BMP C120: Temporary and Permanent Seeding
BMP C130: Surface Roughening
BMP C131: Gradient Terraces
BMP C200: Interceptor Dike and Swale
BMP C204: Pipe Slope Drains
7. Protect Drain Inlets
To prevent sediment from entering drainage systems prior to site stabilization, install catch basin protection
within onsite and nearby downstream catch basins. See Figure C- 9 Protect Drain Inlets-Bag Filter and Figure
C- 10 Protect Drain Inlets-Inlet Gravel and Filter Fabric for acceptable methods of catch basin protection.
NOTE: Only Standard Detail E-03 is approved for use in City of Auburn right of way.
Applicable BMPs include:
BMP C220: Storm Drain Inlet Protection
8. Stabilize Channels and Outlets
All on-site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from a
Type 1A, 10-year, 24-hour frequency storm for the developed condition. Provide stabilization adequate
to prevent erosion of outlets, adjacent streambanks, slopes, and downstream reaches at the outlets of
all conveyance systems. The best method for stabilizing channels is to line the channel completely with a
blanket product, then add check dams as necessary to function as an anchor and slow the flow of water.
See Figure C- 4 Control Flow Rates-Drainage Swale Cross-Sections (SWMMWW Vol II, pg. 4-62), Figure C-
6 Install Sediment Controls-Straw Wattle Rolls (SWMMWW Vol II, pg. 4-98), and Figure C- 11 Temporary
Channel Liners (SWMMWW Vol II, pg. 4-63).
Page 79 of 94
Applicable BMPs include:
BMP C202: Channel Lining
BMP C122: Nets and Blankets
BMP C207: Check Dams
BMP C209: Outlet Protection
9. Control Pollutants
All pollutants must be disposed of in a manner that does not cause contamination of surface waters. Do not
maintain or repair any heavy equipment or vehicles onsite. Clean any spills immediately. Handle concrete and
concrete waste appropriately. Use BMP C154 Concrete Washout Area for concrete cleanup. See Figure C- 12
Concrete Washout Area A (SWMMWW Vol II, pg. 4-51) and Figure C- 13 Concrete Washout Area B
(SWMMWW Vol II, pg. 4-52).
Applicable BMPs include:
BMP C150: Materials on Hand
BMP C151: Concrete Handling
BMP C152: Sawcutting and Surfacing Pollution Prevention
BMP C153: Materials Delivery, Storage and Containment
BMP C154: Concrete Washout Area
10. Control Dewatering
All discharges to the City sewer system require City and King County approval. This approval process may be
initiated by contacting the City. The City will coordinate the request for a letter of authorization from the King
County Wastewater Treatment Division.
Any dewatering water must be discharged through a stabilized channel to a sediment pond.
11. Maintain BMPs
Maintain and repair temporary erosion and sediment control BMPs as needed. Inspect all BMPs at least
weekly and after every storm event. Remove all temporary erosion and sediment control BMPs within 30 days
after final site stabilization.
12. Manage the Project
Projects shall be phased to the maximum degree practicable and take into account seasonal work limits.
Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended
function. Projects that disturb one or more acres must have site inspections conducted by a Certified
Erosion and Sediment Control Lead (CESCL). Project sites less than one acre may have a person without
CESCL certification conduct inspections. The SWPPP must identify the CESCL or inspector, who shall be
present on-site or on-call at all times.
Applicable BMPs:
BMP C150: Materials On-Hand
Page 80 of 94
BMP C160: Certified Erosion and Sediment Control Lead
BMP C162: Scheduling
13. Protect Low impact Development BMPs
Clearly mark limits of Low Impact Development (LID) BMPs with web fencing or silt fencing. Maintain
and repair LID BMPs such as rain gardens and bioretention areas as needed. Inspect all BMPs at least
weekly and after every storm event. Restore on-site stormwater management BMPs to design
conditions at the end of the project.
Page 81 of 94
Figure C- 1 Sample Erosion and Sediment Control Plan
Page 82 of 94
Figure C- 2 Establish Construction Access-Construction Entrance
Page 83 of 94
Figure C- 3 Control Flow Rates/Install Sediment Controls -Sediment Trap Cross-Section & Outlet
(SWMMWW Vol II, pg. 104)
Page 84 of 94
Figure C- 4 Control Flow Rates-Drainage Swale Cross-Sections (SWMMWW Vol II, pg. 4-62)
Page 85 of 94
Figure C- 5 Install Sediment Controls-Silt Fence
Page 86 of 94
Figure C- 6 Install Sediment Controls-Straw Wattle Rolls (SWMMWW Vol II, pg. 4-98)
Page 87 of 94
Figure C- 7 Protect Slopes – Erosion Blankets and Turf Reinforcement Mats (SWMMWW Vol II, pg.
4-25)
Page 88 of 94
Figure C- 8 Tarp Covering
Page 89 of 94
Figure C- 9 Protect Drain Inlets-Bag Filter
Page 90 of 94
Figure C- 10 Protect Drain Inlets-Inlet Gravel and Filter Fabric
Page 91 of 94
Figure C- 11 Temporary Channel Liners (SWMMWW Vol II, pg. 4-63)
Page 92 of 94
Figure C- 12 Concrete Washout Area A (SWMMWW Vol II, pg. 4-51)
Page 93 of 94
Figure C- 13 Concrete Washout Area B (SWMMWW Vol II, pg. 4-52)
Page 94 of 94