HomeMy WebLinkAboutPermit File BLD-2023-0162 2313 R Avenue ♦T Y �
Storm Water Drainage Report
Minimum Requirements 1 through 5
�49�w� Minimum Requirement 1 through 9
L ` 0� ENGINEERING DEPARTMENT
904 6th Street Anacortes, WA 98221
www.anacorteswa.gov
Official Use Only: (Information to Inspectors)
Required Storm Water Facility and other related requirements:
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Project Address: 2313 R Ave Anacortes, WA Submittal Date: 04•lO •ZoZ3
Parcel Number: P77984 Revision Number: I—
Permit Number: Reviewer:
FRONT OF REPORT: Acceptance Date (COA): Q:3,
Submittal Checklist: (All items listed below are required for a complete submittal)
o Cover Sheet (Preparer to Provide): Project title, Location, Revision dates, Engineer's Stamp
o TAB 1: Minimum Requirement#1 -Preparation of Stormwater Site Plans
o TAB 2: Minimum Requirement#2-Construction Stormwater Pollution Prevention (SWPP)
o TAB 3: Minimum Requirement#3-Source Control of Pollution
o TAB 4: Minimum Requirement#4-Preservation of Natural Drainage Systems and Ouffalls
o TAB 5: Minimum Requirement#5-On-site Stormwater Managements
o TAB 6: Minimum Requirement#6-Runoff Treatment
o TAB 7: Minimum Requirement#7-Flow Control
o TAB 8: Minimum Requirement#8-Wetland Protection
o TAB 9: Minimum Requirement#9-Operation and Maintenance
o APPENDIX 1 - Survey performed by a Professional Land Surveyor
o APPENDIX 2- Soils Analysis (Volume 1, Chapter 3.1.1)
o APPENDIX 3- Model Soil Management Plan for BMP T5.13
o APPENDIX 4- Determining Construction Site Sediment Damage Potential (Appendix 7)
o APPENDIX 5 - Site Plan with all applicable information (Minimum Size 11x17-30 scale)
o APPENDIX 6- Documented Site Photos (North, South, East and West)
o APPENDIX 7- Drainage BMP Facility Maintenance Covenant, if applicable. To be recorded prior to the
Temporary Certificate of Occupancy, Certificate of Occupancy or Final Acceptance.
o APPENDIX 8-Maintenance and Operations Manual
Stormwater Management Requirements:
o Refer to the 2019 Department of Ecology Manual
o See also, City of Anacortes Municipal Code 19.76 for additional information
o See also, current Engineering Development Standards, Chapter 2- Storm Drainage for additional
information.
Version Date: August 30, 2022
Project Description and Summary:
Summary Table
Existing Proposed
Development Type Park/Recreation Park/Recreation
Number of Lots 1 1 1
Lot Acreage in SF 52,261 52,261
Soil Type(s) Xerorthents
Site Sediment Transport Score Hi h\Low Low Coy
Depth to Ground Water Table (Feet and Inches) 30-48 ft
See completed Soils Analysis Volume 1, Chapter 3.1.1
Infiltration Rate during Rainy Season Inch\Per Hour) n/a
Impervious Surface on-site) 14,870 so ft 23 205 so ft
Impervious Surface off-site) no off-site runoff
New and Replaced Hard Surface Total (SF) 23,205 sq ft
Lot Coverage (Percentage) 28% 44%
BMP (Required Minimum Requirement 5) BMP T5.13 Post Construction Soils
Water Quality Method Minimum Requirement 6 Vegetated Filter Strip
Water Quantity Method Minimum Requirement 7 not required (discharges to salt water)
Existing Site Conditions Summary:
(Additionally, provide information on previous permits, if any, like Grade and Fill, Clear and Grade, topography,
vegetation, drainage, Critical Areas adjacent to the site and how it may affect this project if soils are disturbed,
Soils Type (Included in Soils Analysis Report), Erosion Problem Areas, Construction PhasinglSequence)
The existing site is a 1.2ac park with a concrete skate park covering 10 889sg ft and approximately 37 392sa ft of
landscaped grass. There is also 2 392sg ft of asphalt parking and 1,588 so ft of sidewalks The site has minimal slope
with elevations ranging from 30-35ft across the 1.2 acres There is a storwater swale that runs along the eastern side of
the property, running along the Tommy Thompson Trail that conveys general runoff south to the storm drainage
network of basin F04. The impervious areas on site are collected and conveyed to the north as part of storm basin F03
Soils on site are comprised of top soil artificial fill and glaciomarine drift deposits
Developed Conditions Summary:
(Additionally, to be shown on the site plan. Identify cut and fill areas, proposed slopes of all hard
surfaces, proposed contours)
The proposed development will increase the impervious area by 8 336sq ft with the expansion of parking and the
addition of an asphalt pump-track on the north side of the skate park.The existing skate park will be removed and
replaced with minor changes to the footprint. The existing parking lot will be removed and replaced mostly with
landscaping (grass) and an enlarged parking lot will be placed on the south end of the property.All cut/fill slopes will be
planted with grass an a or ess.
Drainage Basin (2007 Storm Comp Plan— City website\publicworks\engineering\comprehensive plans):
What Drainage Basin are you in?F04 and F03 Identify any downstream drainage issues (Storm Comp Plan:
If so, describe:
Portions of the site exist in both basin F04 and F03. There are no downstream drainage issues in either basin
Complete the Applicability Requirements— Flow Chart (See next page(s)
- Highlight the path and attach
Version Date: August 30, 2022
Start Here
Does the Site have 3590 Yes See Redevelopment Project
or more of existing hard Thresholds and the Figure "Flow
surface covera e7 Chart for Determining
Requirements for Redevelopment",
No
Does the Project convert 3/4
acres or more of vegetation to
oes the Project result i lawn or landscaped areas, or
5,000 square feet, or No convert 2.5 acres or more of
greater, of new plus native vegetation to pasture?
replaced hard surface
area?
No
Yes
Yes Does the Project result In 2,000
square feet, or greater, of new plus
All Minimum Requirements replaced hard surface area?
apply to the new and replaced
hard surfaces and converted
vegetation areas, No JJrYes
Does the Project have land
Minimum Requirements #1 disturbing activities of 7,000
through #5 apply to the new Yes
square feet or greater?
and replaced hard surfaces
and the land disturbed. No
Minimum Requirement #2
applies.
Flow Chart for Determining Requirements for
New Development
DEPARTMENT OF Revised March 2019
ECOLOGY Please see htlpJAvww.ecy.wa.govlcopyright.html for copyright notice Including permisslons,
State of Washington limitation of Ilablllty,and disclaimer.
Version Date: August 30, 2022
TAB 1 (MINIMUM REQUIREMENT#1)
• 1-3.4.1 Minimum Requirement#1 —Prepare a Stormwater Site Plan
111.3.2—Preparation of a Stormwater Site Plan
Note: The level of detail needed for each step depends upon the project size. Provide a narrative
description of each step.
Step 1 —Analyze Existing Stie Conditions to Determine LID Feasibilitv
The existing site analysis is intended to determine the pre-development conditions on the site in
addition to determining the appropriateness for use of Low Impact Development(LID)techniques.
Site conditions as identified in this step will determine the feasibility of the overall stormwater
design including use of LID techniques. The development context shall be established by an
existing site analysis consistent with the requirements detailed in this Step.
The initial inventory and analysis process will provide baseline information necessary to design
strategies that utilize areas most appropriate to evaporate, transpire, and infiltrate stormwater,
and achieve the goal of mimicking the pre-development natural hydrologic conditions on the site.
The existing site analysis shall include, at a minimum, the following information:
1. A survey prepared by a registered land surveyor, civil engineer, or other qualified
professional showing: (See this section for additional items to include)
2. A soils report prepared by a professional soil scientist certified by the Soil Science Society of
America (or an equivalent national program), or by other suitably trained persons working
under the supervision of a professional engineer, geologist, hydrogeologist, or engineering
geologist registered in the State of Washington.
The sitp sunypyt was performed by 360 Sun Pving on 7/1 F/29 The attached Pxicting conditinnc chpPt
shows the results of this survey
The geotechnical report was compiled by GeoTest Services Inc., dated 03/30/22 and is attached as a
separate document.
Step 2 - Prepare Preliminary Development Layout
Based upon the existing site analysis results, locate the buildings, roads, parking lots, landscaping
features, LID BMPs, and preliminary location of Runoff Treatment and Flow Control BMPs for the
proposed development. Consider the following points when laying out the site:
• Fit development to the terrain to minimize land disturbance; confine construction activities to
the least area necessary, and away from critical areas.
• Preserve areas with natural vegetation (especially forested areas) as much as possible.
• On sites with a mix of soil types, locate impervious areas over less permeable soil (e.g., till),
try to restrict development over more porous soils or take advantage of them by locating
bioretention, rain gardens and/or permeable pavement over them.
• Cluster buildings together.
• Minimize impervious areas.
• Maintain and utilize the natural drainage patterns.
Proposed development was placed as close as possible to overlap with the existing features they are
replacing. Runoff Treatment is located to capture all runoff from pollution generating surfaces
Version Date: August 30, 2022
Step 3- Perform Off-site Analysis
City of Anacortes requires an off-site analysis for projects that add 5,000 SF or more of new
hard surfaces, or convert% acres of vegetation to lawn or landscape areas, or convert 2.5
acres of forested area to pasture.
Off-site analysis extends to mile downstream of the project site.
The downstream runoff from the skate nark features will be gollected an conveyed to the network of
Stormwater Basin F03 and flow to Fidalgo Bay.
The runoff from vegetation portions of the site and the new parking lot will enter a grass swale system
that runs along the eastern boundary of the property, adiacent to the Tommy Thompson Trail The
swale runs north to a culvert under the trail, then south where it enters the F04 Basin conveyance
network and is discharged to Fidalgo Bay.
See Basin F03 and F04 Stormwater Modeling Analysis by Gray& Osborne, provided in Tab 4.
Step 4— Determine and Read the Applicable Minimum Requirements (Place at the front end of
the document before MR#7)
1-3.3 Applicability of the Minimum Requirements establishes project thresholds for the
application of Minimum Requirements to new development and redevelopment projects. Figure
1-3.1: Flow Chart for Determining Requirements for New Development (Included in the report)
and Figure 1-3.2: Flow Chart for Determining Requirements for Redevelopment (Included in
the report) provide the same thresholds in a flow chart format. Based on the preliminary
layout, determine whether Minimum Requirements#1 and #2 only apply to the project, or#1
through#5 only apply to the project, or#1 through#9 apply.
Minimum requirements#l-#q w ill agpl)t to the project Minimum requirement#7 daes not apply
because conveyance from the site discharges to saltwater. Minimum requirement#8 does not apply
because there are no wetlands in the vicinity or downstream
Step 5- Prepare a Permanent Stormwater Control Plan (Place in Appendix 5 of this report)
(Due to the extent of required information for this section, refer to this section of the Ecology
Manual for requirements.)
Presented as a Separate document. Gee attache.
Version Date: August 30, 2022
Step 6 - Prepare a Construction Stormwater Pollution Prevention Plan (Place in MR#2— 13
Elements)
The Construction SWPPP for projects adding or replacing 2,000 square feet of hard surface or
more, or clearing 7,000 square feet or more, must contain sufficient information to satisfy the
local government Plan Approval Authority that the potential pollution problems have been
adequately addressed for the proposed project. Local governments may adopt a standard
SWPPP format for use by projects less than 1 acre. An adequate Construction SWPPP
includes a narrative and drawings. The narrative is a written statement to explain and justify the
pollution prevention decisions made for a particular project. The narrative contains concise
information concerning existing site conditions, construction schedules, and other pertinent
items that are not contained on the drawings. The drawings and notes describe where and
when the various BMPs should be installed, the performance the BMPs are expected to
achieve, and actions to be taken if the performance goals are not achieved.
See II-2.4 Preparing Construction SWPPPs for details about what to include in the project's
Construction SWPPP.
A complete construction SWPPP has been prepared for this cit
Step 7- Complete the stormwater site plan
The Stormwater Site Plan encompasses the entire submittal to the Local Agency with drainage
review authority. Refer to this section of the Manual for further clarification of each item
and what is required. See below:
A. Project Overview (Front End)
B. Existing Conditions Summary (Front End)
C. Off-site Analysis Report (Minimum Requirement 1, Step 3)
D. Permanent Stormwater Control Plan (Appendix 5)
E. Construction Stormwater Pollution Prevention Plan (Minimum Requirement 2)
F. Special Reports and Studies (Survey—Appendix 1, Geotechnical —Appendix 2, all
others placed after Appendix 8)
G. Other Permits, if applicable
H. Operation and Maintenance Manual (Appendix 8)
I. Declaration of Covenant for Privately Maintained Flow Control and Treatment Facilities.
(See attached Drainage BMP Maintenance Covenant BMP Agreement) (Appendix 7)
J. Declaration of Covenant for Privately Maintained On-site Stormwater BMP's (See
attached Drainage BMP Maintenance Covenant BMP Agreement) (Appendix 7)
K. Bond Quantities Worksheet, if applicable
Version Date: August 30, 2022
Step 8 - Check Compliance with all Applicable Minimum Requirements
i
Before Submitting this report, a Stormwater Site Plan as designed and implemented should
specifically fulfill all Minimum Requirements applicable to the project. The Stormwater Site Plan
should be reviewed to check that these requirements are satisfied.
f
Note: The report will be returned if determined incomplete.
A summary of the minimum requirements and where each is addressed is included in the Stormwater
Site Plan. See Tab 6.
I
Version Date: August 30, 2022
Stormwater
Site Plan
Ben Root Skate Park
Anacortes, WA
March 7, 2023
PREPARED FOR:
City of Anacortes
Contact: Jonn Lunsford
Phone: (360) 299-1953
CLIENT:
WAgy�H�
Grindline Skateparks, Inc.
4619 14th Ave SW
Seattle, WA 98106
�O�f RF 43952 Q
NAL � MacKay Sposito Prepared by:
03/10/2023 Project Number: 17811 Eric Pilcher, PE
Federal Way Office
MacKay+ SPOSIto 33810 Weyerhaeuser Way South,Suite 130• Federal Way, WA 98001
253.205.8700 • info@mackaysposito.com
Ben Root Skate Park
MacKay+SPOSItO Stormwater Site Plan
March 7,2023
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Ben Root Skate Park
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Table of Contents
1.0 Project Overview.....................................................................................................................:........5
2.0 Existing Conditions Summary...........................................................................................................9
Topography............................................................................... ..................................9
Soil..........................................................................................:..............................:................................9
Vegetation..............................................................................................................................................9
3.0 Off-Site Analysis...............................................................................................................................9
4.0 Permanent Stormwater Control....................................................................................................10
DevelopedSite Hydrology....................................................................................................................10
RunoffTreatment................................................................................................................................10
Discharge Area Summary:.....................
5.0 Special Reports and Studies...........................................................................................................19
6.0 Other Permits.................................................................................................................................19
7.0 Declaration of Covenant for On-site Stormwater Management BMPs.....:...................................19
8.0 References.....................................................................................................................................19
List of Tables
Table 1.Summary of Minimum Requirements.............................................................................................6
Table 2. Discharge Area Impacts.................................................................................................................11
List of Fi¢ures
Figure 1. Location Map.,................ ..........................................
...................... • 7
Figure2. Area Storm Network....................................................................................................................13
Figure 3. Impervious Surfaces Site Plan......................................................................................................15
Figure4. Stormwater Site Plan...................................................................................................................17
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Ben Root Skate Park
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1.0 "PROJECTOVERVIEW
The project involves the demolition of existing skate park amenities and replacement with a new skate
park facility within the same general location with the addition of a pump track in place of the current
parking lot, and re-location of the parking facility to the south end of the property. The project site is
located on a 1.1-acre parcel (P77984) located at 2313 R Avenue, Anacortes, WA 98221 (see Figure 1).
Project improvements include a new asphalt parking area with curb, gutter, and drainage structures, a
concrete pedestrian path, 10,184 square foot concrete skate park and a 3,548 square foot pump track.
The existing skate park and parking lot will be demolished and an existing open space and art installation
on the north end will remain.Approximately 0.93 acres will be disturbed.
The City of Anacortes has adopted the 2019 Edition of the Washington State Department of Ecology
(Ecology)Stormwater Management Manual for Western Washington (SWMMWW).
Since the site contains less than 35% of existing impervious coverage, this project is classified as new
development. The project will result in more than 2,000 square feet of new plus replaced hard surface
area,and disturb more than 7,000 square feet;therefore, minimum requirements#1 through#9 will apply
to the new and replaced hard surfaces and the land disturbed.A summary of the minimum requirements
is provided in Table 1 below.
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Ben Root Skate Park
MacKay+SPOSItO Stormwater Site Plan
March 7,2023
Table 1. Summary of Minimum Requirements
MR# Requirement Description Requirement Summary Location Addressed
1 Stormwater Site Plan (SSP) A SSP is required to address This document
minimum requirements per
the SWMMWW.
2 Construction Stormwater A SWPPP is required to Tab 2 of the City Worksheet;
Pollution Prevention Plan address stormwater pollution Attachment A
(SWPPP) during construction.
3 Source Control Based on the site's land use, Tab 3 of the City Worksheet;
post-construction best 0&M Plan
management practices
(BMPs) are mandatory
and/or recommended.
4 Preserve Natural Drainage There will be no disruption to Tab 4 of the City Worksheet;
Systems any natural drainages. Section 3.0, this document
5 On-Site Stormwater Past-Construction Soil Tab 5 of the City Worksheet;
Management Quality and Depth shall be Section 4.0,this document
met..
6 Runoff Treatment The project contains 8,000 Section 4.0, this document
square feet of new or
replaced impervious
surfaces and will have runoff
treatment as part of the new
site deisgn.
7 Flow Control The project flows to Fidalgo Not applicable
Bay, a salt water body.
8 Wetlands Protection No wetlands are on or Not applicable
adjacent to the site.
9 Operation and Maintenance Maintenance for the on-site Tab 9 of the City Worksheet;
(O&M) runoff treatment will need to Attachment C
be addressed.
6 Page
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PROJECT LOCATION1-9
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VICINITY MAP
NOTTOSCALE
MacKays PROJECT NO.: 17811
Sposito ANACORTESSKATEPARK DRAWN BY: MBM
33030 FEDERALWAY, WAY 001 130 LOCATION MAP
FEDERAL WAY,WA seoon CHECKED BY: ELF
PHONE(253)205-8700
www.mackaysposito.com DATE: NOV 2022
SHEET NO. FIGURE 1
Ben Root Skate Park
MacKay+SPOSItO Stormwater Site Plan
March 7,2023
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Ben Root Skate Park
MacKay+Sposito Stormwater Site Plan
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1 EXISTING CONDITIONS
Topography
The 1.1 acre project site contains an existing±10,900 square foot paved skate park,±2,400 square foot
asphalt parking lot.The site is accessed via R Avenue.The site is bounded by R Avenue to the west,the
Tommy Thompson Trail to the east, and a vacant industrial lot on the south.The skate park sits within
the larger Alice Parchman Newland Park.
The existing skate park sits at an elevation of approximately 33 with the site sloping gently toward the
east-northeast with a shallow grass lined swale separating the park from the walking trail to the east.
Soil
A Custom Soil Resource Report for Skagit County Area, Washington at Ben Root Skate Park (NRCS 2021;
Appendix C) indicates that native soils classified as Xerorthents extremely gravelly sandy loam. This soil
classification is described as being well drained,with a moderately high capacity.
A geotechnical report was prepared by GeoTest Services Inc(GeoTest 2022:Appendix C).Test borings
and laboratory tests found 0.5-2 feet of loose gravelly silty sand over top of 10+feet of stiff sandy clay.
The report concludes that infiltration is not recommended due to poor soil infiltration rates and
seasonal perched groundwater.
Vegetation
The site has been previously cleared and graded.Revegetation from prior development is limited to grass
lawn,fields,and landscaping trees.
The site is split within two City of Anacortes outfall basins: Basin F03, draining towards the 22nd Street
outfall and Basin F04,draining toward the 28th Street outfall.Runoff generated form the northern portion
of the site, including the existing skatepark and parking lot, is routed to municipal storm sewer along
R Avenue and routed east at 22nd Street to the basin F03 outfall into Fidalgo Bay.
Runoff generated from the southern, vegetated portion of the site is directed to a swale located on the
eastern border adjacent to the Tommy Thompson Trail.The swale ends at a municipal storm drain along
T Avenue, north of 28th Street, which discharges east to the Basin F04 outfall into Fidalgo Bay (see
Figure 2).
The proposed improvements will continue to drain in the same manner. No alterations are being made to
downstream drainage conveyances.
Downstream analysis of existing infrastructure within Basins F03 and F04 was recently performed by Gray
&Osborne,Inc. The analysis considered all contributing basins to be fully built out based on the maximum
impervious cover allowed by zoning. Even with this overly conservate approach,none of the pipes within
9 1 P a g e
Ben Root Skate Park
MacKay+SPOSItO Stormwater Site Plan
March 7,2023
Basin F03 or F04 downstream of Ben Root Skatepark were identified as surcharged or contributing to a
surcharged condition.A copy of the analysis is attached to Tab 4 in the main Storm Water Drainage Report.
aPERMANENT STORMWATIEKOONTROL
Developed Site Hydrology
10,889 square feet of existing non-pollution generating hard surface (NPGHS) will be removed and
replaced with 13,732 square feet, resulting in 2,842 square feet of new NPGHS. 2,392 square feet of
pollution generating hard surface (PGHS) will be removed and replaced with 8,447 square feet of new
PGHS(see Figure 3).
The increase in PGHS will necessitate runoff treatment controls. For this project, a vegetated filter strip
has been designed to fulfill treatment requirements.The placement of the filter strip will treat all runoff
from the new PGHS area and discharge it into an existing swale that collects runoff around the Tommy
Thompson Trail and is conveyed to a discharge point in Fidalgo Bay. All stormwater from this site is
discharged into Fidalgo Bay, a salt water body, making the project exempt from flow control.
An additional 14,356.33 square feet of existing lawn area will be disturbed and re-vegetated in kind as
non-pollution generating pervious surface (NPGPS).
Runoff Treatment
The filter strip was sized using the SWMMWW section V-7, BMP T9.40. Using WWHM2012 software, the
water quality flow rate of 0.0256cfs was established.The strip was sized at 38 feet wide, 17 feet long,and
a slope of 4%to achieve the required residence time and flow depth,and velocity. Due to site constraints,
the filter strip design will be 18 feet long on the south edge and 16 feet long on the north edge,which will
allow the strip to fit more naturally to the site contours and minimize disturbance.Sheet flows from the
asphalt parking area will be flow through curb cuts,18 inches in length,and spaced 7 feet on center along
the boundary between the parking lot and the filter strip.A gravel flow spreader along the length of the
filter strip will be placed 1" below the edge of the parking lot as the entrance to the vegetated filter strip.
For additional construction details of the filter strip,see the construction documents and Figure 4.
Discharge Area Summary
Impacts to each threshold discharge area are summarized in Table 2.
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Ben Root Skate Park
+SPOSItO Stormwater Site Plan
March 7,2023
Table 2. Discharge Area Impacts
Discharge City Storm Replaced Hard New Hard New+Replaced Converted
Area Basin Surface',' Surface',' Hard Surface',' Vegetation
Basin 1 F04 385 8,062 8,447 N/A
Basin 2 F03 14,485 274 14,759 N/A
Site Total 14,870 8,336 23,206 N/A
Discharge City Storm New+Replaced New+Replaced Runoff Flow Control
Area Basin NPGHSI,2 PGHS',' Treatment
Basin 1 F04 831 7,616 Vegetated Not required
Filter Strip
Basin 2 F03 14,759 0 Not required Not required
Site Total 15,590 7,616
Notes:
1.All areas are in square feet.
2. Calculations reflect on-site areas only and do not include portions of the R Avenue right-of-way.
3.The site has been previously developed; no previously undisturbed areas will be converted to lawn.
NPGHS= Non-pollution generating hard surface(e.g.,sidewalks,skate park, pump track)
PGHS= Pollution generating hard surface(e.g., parking lot)
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March 7,2023
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March 7,2023
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MacKay.,spoSito Stormwater Site Plan
March 7,2023
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Ben Root Skate Park
MacKay+SPOSItO Stormwater Site Plan
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5.0 SPECIAL REPORTSD STUDIES
Aside from the geotechnical investigation described in section 2.0,no special reports or studies have been
conducted or are required for the site.
. 9 OTHER
No additional permits are required that affect the drainage plan or contain more restrictive drainage-
related requirements.
There are no covenants for on-site stormwater management BMPs.The site will be publically maintained.
Ecology 2019. Stormwater Management Manual for Western Washington, Publication Number 19-10-
21. Washington State Department of Ecology,Water Quality Program, Lacey,WA.July.
GeoTest 2022. Geotechincal Engineering Report Anacortes Skate Park. GeoTest Services Inc., Belingham,
WA. March 30, 2022.
NRSC 2022. Custom Soil Resource Report for Skagit County Area, Ben Root Skate Park. U.S. Department
of Agriculture, Natural Resource Conservation Service, https://websoilsurvey.sc.egov.usda.gov/
Downloaded Oct 13
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TAB 2 (MINIMUM REQUIREMENT#2)
See attached SWPPP report
Version Date: August 30, 2022
Construction
Stormwater
Pollution
Prevention Plan
Ben Root Skate Park
Anacortes, WA
March 7, 2023
PREPARED FOR:
City of Anacortes
Contact: Jonn Lunsford
P j�C CLIENT:
Of WASyyh�C� Grindline Skateparks Inc.
4619 14th Ave SW
Seattle, WA 98106
R 3952 FG O
S G MacKay Sposito Prepared by:
s/ONAL E� Project Number: 17743 Eric Pilcher, PE
03/10/2023
Federal Way Office
MacKay q r' Sposito 33810 Weyerhaeuser Way South,Suite 130• Federal Way, WA 98001
253.205.8700 • info@mackaysposito.com
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Ben Root Skate Park
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Construction Stormwater Pollution
Prevention Plan (SWPPP)
for
Ben Root Skate Park
Prepared for:
City of Anacortes,
Department of Ecology, Shoreline Northwest Regional Office
Perm ittee/ Owner Developer Operator/ Contractor
City of Anacortes Anacortes Parks Dept TBD
904 611 St 904 611 St
Anacortes, WA 98221 Anacortes, WA 98221
Contact: Contact: John Lunsford
(360) 293-1918 (360) 299-1953
2313 R Avenue, Anacortes, WA 98221
Skagit Co. Tax Parcel P77984
Erosion and Sediment Control Lead
Name Organization Contact Phone Number
TBD TBD TBD
SWPPP Prepared B
Name Organization Contact Phone Number
Eric Pilcher, PE MacKay Sposito (253) 237-7932
33810 Weyerhaeuser Way S
Suite 130
Federal Way, WA 98001
SWPPP Preparation Date
March 7, 2023
Proiect Construction Dates Tentative
Activity / Phase Start Date End Date
-_q
Skate Park Removal & Spring 2023 Fall 2023
Replacement
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Table of Contents
1.0 General Information ........................................................................................................................7
ProjectDescription.................................................................................................................................7
ExistingSite Conditions..........................................................................................................................7
AdjacentAreas........................................................................................................................................7
CriticalAreas............................................................................................................................................7
Soil..........................................................................................................................................................8
PotentialErosion Problems....................................................................................................................8
2.0 Required Construction SWPPP Elements.........................................................................--............8
Element#1: Preserve Vegetation/Mark Clearing Limits.........-.............................................................8
Element#2: Establish Construction Access............................................................................................9
Element#3:Control Flow Rates..........................................................................................,..................9
Element#4: Install Sediment Controls................................................................................. .................9
Element#5:Stabilize Soils......................................................................................................................9
Element#6: Protect Slopes..................................................................................................................10
Element#7:Protect Drain Inlets..........................................................................................................10
Element#8:Stabilize Channels and Outlets.........................................................................................10
Element#9:Control Pollutants............................................................................................................10
Element#10:Control De-Watering......................................................................................................11
Element#11: Maintain BMPs...............................................................................................................11
Element#12: Manage the Project..................................................... ...................................................11
Element#13: Protect Low Impact Development BMPs.......................................................................12
3.0 Construction Schedule and Phasing...............................................................................................13
4.0 References......................................................................................................................................14
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Ben Root Skate Park
Construction SWPPP
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List of Tables
Table1.Construction Schedule............................................... .................................................................13
List of Attachments
Attachment A. Construction Drawings(Submitted as Separate File)
Attachment B.Soil Reports (See Stormwater Site Plan,Appendix C)
Attachment C.Construction BMPs
Attachment D. Construction Stormwater Site Inspection Form
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1.0 GENERAL INFORMATION
Project Description
The project involves the demolition of existing skate park amenities and replacement with a new skate
park facility within the same general location with the addition of a pump track in place of the current
parking lot, and re-location of the parking facility to the south end of the property.The project site is
located on a 1.1-acre parcel (P77984) located at 2313 R Avenue Anacortes,WA 98221. Project
improvements include a new asphalt parking area with curb,gutter,and drainage structures,a concrete
pedestrian path, 10,184 square foot concrete skate park and a 3,548 square foot pump track.The
existing skate park and parking lot will be demolished and an existing open space and art installation on
the north end will remain.Approximately 0.93 acres will be disturbed.
Earthwork activities associated with the new improvements are expected to require approximately 230
cubic yards of excavation and 980 cubic yards of fill.The source of import material is undetermined at
this time.
Runoff associated with the skate park will collect within the skate park"bowl",which will then be piped
to the existing pump-out structure within the park and drain to the stormwater conveyance in R Avenue.
This conveyance connects to a trunkline in 22"d Street and is emptied into Fidalgo Bay.
Existing Site Conditions
The 1.1 acre project site contains an existing±10,900 square foot paved skate park,±2,400 square foot
asphalt parking lot.The site is accessed via R Avenue.The site is bounded by R Avenue to the west,the
Tommy Thompson Trail to the east,and a vacant industrial lot on the south.The skate park sits within
the larger Alice Parchman Newland Park.
The existing skate park sits at an elevation of approximately 33 with the site sloping gently toward the
east-northeast with a shallow grass lined swale separating the park from the walking trail to the east.
Adjacent Areas
The skate park area is surrounded by Alice Parchman Newland Park, a linear greenbelt park including
walking paths and sculptures.The vicinity has minimal slope throughout with runoff from R Avenue
collected in roadside gutters and catch basins and a gradual drainage swale along the eastern border
along the Tommy Thompson Trail.The vacant lot on the south is covered by cracked asphalt and
concrete slab foundation.The lot is graded flat and is separated from the park by a chain link fence with
a buildup of brush and vegetation at the base
Construction traffic will access the site via R Avenue(public) which shall be protected from vehicle track-
out during construction.
Critical Areas
There are no streams, lakes, or wetlands that may be impacted by construction activities.There are no
known critical areas on or adjacent to the site.
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Soil
A Custom Soil Resource Report for Anacortes,Washington at Ben Root Skate Park(NRCS 2022;Appendix
C) indicates that native soils classified as Xerorthents.This soil classification is described as being well
drained,with a low erosion potential and high infiltration capacity.
A geotechnical report was prepared by GeoTest Services Inc. (GeoTest 2022:Appendix C).Test borings
and laboratory tests found 0.5-2 feet of loose gravelly silty sand over top of 10+feet of stiff sandy clay.
The report concludes that infiltration is not recommended due to poor soil infiltration rates and
seasonal perched groundwater.
Potential Erosion Problems
There are no known erosion problems currently on the site.
i • 1 ® • PIP ELEMENTS
The following are standard elements of the Construction SWPPP, addressed as relevant to the work to
be performed to accommodate Ben Root Skate Park. More information on listed BMPs is available in
Attachment C.
The BMPs listed within this SWPPP are the basic minimum that are required for temporary erosion and
sediment control(TESL). It maybe necessary to deploy other TESC BMPs depending on actual site and
weather conditions. Refer to Volume II, Chapter 3 of the Stormwater Management Manual for Westerns
Washington (Ecology 2019)for the complete list.
Element#1. Preserve Vegetation/Mark Clearing Limits
Prior to land disturbing activities,including clearing and grading,the limit of disturbance (i.e.,clearing
limits)shall be clearly demarcated with plastic, metal,or fabric fence. High visibility silt fence may be
used as demarcation as well as for erosion control purposes, provided it is installed in a manner that
serves both functions.
The site has been previously developed, and non-paved areas have been grassed with no further
revegetation. Ordinarily,topsoil strippings from previously undisturbed areas within the clearing limit
would be stockpiled on-site for reuse to the extent practical. However,the material underneath the
existing sod is not expected to be of high topsoil quality,so is not required to be retained for this site.
Clearing shall be limited to the extents necessary to perform the work.Vegetation outside the limit of
work shall remain protected during installation of the skate park.
There are no critical areas on site that require buffer zones.
Best management practices(BMPs)to be deployed include:
• BMP C101: Preserving Natural Vegetation
• BMP C103: High Visibility Fence (Tree Protection Fence)
• BMP C233:Silt Fence
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Element#2: Establish Construction Access
All construction vehicles shall access the site via R Ave(public)where a stabilized construction
entrance/exit shall be installed.Access point conditions shall be monitored for track-out. In the event
that soil is tracked out of the site,the soil shall be removed by shoveling,sweeping,etc.
BMPs to be deployed include:
• BMP C105:Stabilized Construction Entrance/Exit
Element#3: Control Flow Rates
Runoff shall be collected within the footprint of the skate park"bowl',which shall act as a temporary
sediment trap. Following settling of sediment,sump pump shall be used to discharge decant water to
the existing Park Street swale at a controlled rate.
BMPs to be deployed include:
• BMP C240:Sediment Trap
Note: Per Ecology 2019,the required sediment trap surface area is 2080 square feet per cfs of inflow
based on a 2-year storm event. The site contains 1.20 acres,of which 0.78 acres will be disturbed. The
resultant 2-year developed runoff from WWHM12 is 0.2040 cfs.
SA(min.)=2080 SF * 0.2040 cfs=425 SF(nominal)
The existing skate bowl is 4 feet deep with an average length to the width ratio of 6 and average side
slopes of 2 horizontal to 1 vertical. The bottom of the bowl is at elevation 28.3 and the rim is at 32.3. At
elevation 30(e.g., a depth of 1.7 feet),the surface area measures 3750, which exceeds the minimum
required sediment trap area by a factor of more than 8.
Element#4: Install Sediment Controls
Effective erosion and sediment controls are necessary to minimize the discharge of sediment to
undisturbed portions of the site, and existing and proposed stormwater management facilities.
Sediment control BMPs shall be installed as one of the first steps during clearing and grading.They shall
be fully functional prior to other land disturbing activities.
BMPs to be deployed include:
• BMP C233:Silt Fence
• BMP C240:Sediment Trap
Element#5:Stabilize Soils
Exposed and unworked soils, including stockpiles,shall be stabilized within 7 days during the dry season
(i.e., May 1—September 30), and within 2 day days the wet season (i.e.,October 1—April 30). In
addition, soils shall be stabilized by end of shift prior to holidays and weekends, as needed based on
weather forecasts.
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BMPs to be deployed include:
• BMP C120:Temporary and Permanent Seeding
• BMP C121: Mulching
• BMP C125:Topsoiling/Composting
• BMP C140: Dust Control
Element#6: Protect Slopes
There are no significant slopes currently on site.Slopes around the periphery of the skate park and
pump track will be graded at 3:1 or flatter and will be seeded to stabilize.Some locations within the
pump track may have steep slopes that will need plastic coverings during construction to prevent
erosion.
BMPs to be deployed include:
• BMP C223:Silt Fence
Element#7: Protect Drain Inlets
The existing storm basin in the parking lot will be removed, but it's receiving structure in the R Avenue
curb line shall be given inlet protection. In addition the downstream structure at the north end of the
bus lane should receive inlet protection treatment.
BMPs to be deployed include:
• BMP C220: Inlet Protection
Element#8: Stabilize Channels and Outlets
There are no existing or proposed channels on site that require protection.
Element#9: Control Pollutants
Sawcutting of asphalt and concrete will be necessary in order to perform demolition of the existing
paved courts and construct the new skate park.Surfaces to be sawcut shall be wetted during sawing
operations, and the resulting slurry shall be vacuumed and collected for off-site disposal at an
appropriate site.
Similarly, concrete trucks shall not dispose of excess material or be washed-out on site.De minimis
amounts of wash water(i.e.,from tool rinsing) may be disposed behind forms in an area to receive
concrete. However, in no case will concrete wash water be allowed to enter storm drains or be routed
towards stormwater management facilities.
Small quantities of petroleum products (e.g.,5-gallon gas can,quart of oil)for use with powered hand
tools may be stored on-site in a designated area,such as a Conex box. However, refueling of vehicles
shall occur either off-site, or by means of a fueling service. Similarly, non-emergency vehicle
maintenance(e.g., routine oil changes)shall not occur on-site. A spill kit shall be kept within the material
staging area in the event that cleanup becomes necessary.
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BMPs to be deployed include:
• BMP C151:Concrete Handling
• BMP C152:Sawcutting and Surfacing Pollution Prevention
• BMP C153: Material Delivery,Storage, and Containment
Element#10: Control De-Watering
Excavation is limited to dig-out of areas underneath the existing paved courts to form the subgrade for
the skate park bowls.The need for de-watering is not expected; however, in the event that it becomes
necessary,water will be collected at a low spot within the excavation and pumped to a Baker tank(see
Element#3).
Element#11: Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired, as
needed,to assure continued performance of their intended function in accordance with each BMP's
specifications(see Attachment C.)
Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week
and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes
inactive and is temporarily stabilized,the inspection frequency may be reduced to once every calendar
month.
All temporary erosion and sediment control BMPs shall be removed within 30 days after achieving final
site stabilization,or after the temporary BMP is no longer needed.
Trapped sediment shall be removed or stabilized on site. Disturbed soil shall be permanently stabilized
following removal of BMPs and vegetation.
All BMPs installed for the permanent control of stormwater shall be protected from sediment and
compaction. All BMPs that are to remain in place following completion of construction shall be
examined and placed in full operating conditions. If sediment enters a BMP during construction, it shall
be removed and the facility shall be returned to the conditions specified in the construction documents.
BMPs to be deployed include:
• BMP C150: Materials on Hand
Element#12: Manage the Project
The project is expected to be completed within a single phase; however,some elements may need to be
postponed to avoid interfering with peak facility operations (i.e., months of October—December).
All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of
their intended function. Inspections and monitoring shall be performed weekly,and within 24-hours
following a significant storm event.
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This SWPPP shall be maintained and updated as necessary to provided continued protection. In the
event that BMPs shown on the drawings or listed within this SWPPP are not sufficient, additional BMPs
shall be deployed. If needed; additional BMPs may be selected from the SWMMWW,or be site-specific.
Approximately 0.86 acres of total area will be disturbed,therefore a certified erosion and sediment
control lead (CESCL) is not required.Site inspections shall be conducted by a member of the
construction team who has been properly trained to assess the site conditions and construction
activities that could impact the quality of stormwater,and the effectiveness of erosion and sediment
control measures used to control the quality of stormwater discharges.The Erosion Control Lead,
identified on the second title page of this SWPPP,shall:
• Examine stormwater visually for the presence of suspended sediment,turbidity,discoloration,
and oil sheen
• Evaluate the effectiveness of BMPs and determine if it is necessary to install, maintain, or repair
BMPs to improve the quality of stormwater discharges
• Review the SWPPP for compliance with the 13 construction SWPPP elements and make
appropriate revisions within 7 days of an inspection, if necessary
• Immediately begin the process of fully implementing and maintaining appropriate source
control and/or treatment BMPs as soon as possible,addressing the problems no later than
within 10 days of an inspection,when necessary. If installation of necessary treatment BMPs is
not feasible within 10 days,the erosion control lead may request an extension within the initial
10-day response period.
• Document BMP implementation and maintenance in the site log book(see Attachment E)
• Inspect all areas disturbed by construction activities,all BMPs, and all stormwater discharge
points at least once every calendar week and within 24 hours of any discharge from the site.The
erosion control lead may reduce the inspection frequency for temporary stabilized, inactive sites
to once every calendar month.
A copy of this SWPPP(modified as necessary),and copies of all monitoring and inspection logs shall be
maintained on site during construction activities,and made available for review by the owner,tenant,
engineer, City,and Ecology, upon request.
BMPs to be deployed include:
• BMP C150: Materials on Hand
• BMP C162:Scheduling
Element#13: Protect Low Impact Development BMPs
There are no existing or proposed low impact development BMPs on site that require protection.
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Y CONSTRUCTION SEQUENCEAND PHASING
The following sequence is tentative. It is subject to change upon execution of a formal construction
contract.The contractors critical path management schedule and associated updates shall apply,and
this SWPPP shall be modified as necessary.
Table 1.Construction Sequence
Construction Activity
Install TESC BMPs
Sawcutting
Pavement Demolition
Topsoil Stripping
Grading
Base Course Placement
Form,Pour, &Strip Concrete
Striping&Signage
Landscaping/Permanent Seeding
Maintain TESC BMPs throughout the above tasks
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4.0 REFERENCES
Ecology 2019. 2019 Stormwater Management Manual for Western Washington.Washington State
Department of Ecology,Water Quality Program, Lacey, WA.July 2019.
GeoTest 2022. Geotechincal Engineering Report Anacortes Skate Park. GeoTest Services Inc., Belingham,
WA. March 30,2022.
NRSC 2022.Custom Soil Resource Report for Skagit County Area, Ben Root Skate Park. U.S. Department
of Agriculture, Natural Resource Conservation Service, https://wehsoilsurvey.sc.egov.usda.gov/
Downloaded Oct 13.
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Attachment A. Construction Drawings (Submitted as Separate File)
Ben Root Skate Park
MacKay+Sposito construction SWPPP
March 7, 2023
Attachment B. Soil Reports (See Stormwater Site Plan,Appendix Q
Ben Root Skate Park
ly + ;1 Construction SWPPP
March 7,2023
Attachment C. Construction BMPs
BMP C101 : Preserving Natural Vegetation
Purpose
The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site
disturbance is the single most effective method for reducing erosion.For example,conifers can hold
up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never
reach the ground but is taken up by the tree or evaporates.Another benefit is that the rain held in the
tree can be released slowly to the ground after the storm.
Conditions of Use
Natural vegetation should be preserved on steep slopes, near perennial and intermittent water-
courses or swales,and on building sites in wooded areas.
. As required by local governments.
• Phase construction to preserve natural vegetation on the project site for as long as possible
during the construction period.
Design and Installation Specifications
Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines.
The preservation of individual plants is more difficult because heavy equipment is generally used to
remove unwanted vegetation.The points to remember when attempting to save individual plants
are:
• Is the plant worth saving?Consider the location,species,size,age,vigor,and the work
involved. Local governments may also have ordinances to save natural vegetation and trees.
• Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground
disturbance away from the trees at least as far out as the dripline.
Plants need protection from three kinds of injuries:
• Construction Equipment-This injury can be above or below the ground level. Damage results
from scarring,cutting of roots, and compaction of the soil. Placing a fenced bufferzone around
plants to be saved prior to construction can prevent construction equipment injuries.
. Grade Changes-Changing the natural ground level will alter grades,which affects the plant's
ability to obtain the necessary air,water, and minerals. Minor fills usually do not cause prob-
lems although sensitivity between species does vary and should be checked.Trees can typ-
ically tolerate fill of 6 inches or less. For shrubs and other plants,the fill should be less.
When there are major changes in grade, it may become necessary to supply air to the roots of
plants.This can be done by placing a layer of gravel and a the system over the roots before the
fill is made.The tile system should be laid out on the original grade leading from a dry well
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 271
around the tree trunk.The system should then be covered with small stones to allow air to cir-
culate over the root area.
Lowering the natural ground level can seriously damage trees and shrubs.The highest per-
centage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can
cause serious injury.To protect the roots it may be necessary to terrace the immediate area
around the plants to be saved. If roots are exposed, construction of retaining walls may be
needed to keep the soil in place. Plants can also be preserved by leaving them on an undis-
turbed,gently sloping mound.To increase the chances for survival, it is best to limit grade
changes and other soil disturbances to areas outside the dripline of the plant.
. Excavations-Protect trees and other plants when excavating for drainfields, power,water,
and sewer lines.Where possible,the trenches should be routed around trees and large
shrubs.When this is not possible, it is best to tunnel underthem.This can be done with hand
tools or with power augers. If it is not possible to route the trench around plants to be saved,
then the following should be observed:
• Cut as few roots as possible.When you have to cut,cut clean. Paint cut root ends with a
wood dressing like asphalt base paint if roots will be exposed for more than 24-hours.
• Backfill the trench as soon as possible.
• Tunnel beneath root systems as close to the center of the main trunk to preserve most
of the important feeder roots.
Some problems that can be encountered with a few specific trees are:
. Maple, Dogwood, Red alder,Western hemlock,Western red cedar,and Douglas fir do not
readily adjust to changes in environment and special care should be taken to protect these
trees.
. The windthrow hazard of Pacific silver fir and madrona is high,while that of Western hemlock
is moderate.The danger of windthrow increases where dense stands have been thinned.
Other species(unless they are on shallow,wet soils less than 20 inches deep) have a low
windthrow hazard.
• Cottonwoods, maples,and willows have water-seeking roots.These can cause trouble in
sewer lines and infiltration fields.On the other hand,they thrive in high moisture conditions
that other trees would not.
. Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir,Sitka
spruce,Western red cedar,Western hemlock, Pacific dogwood,and Red alder can cause ser-
ious disease problems. Disease can become established through damaged limbs,trunks,
roots,and freshly cut stumps. Diseased and weakened trees are also susceptible to insect
attack.
Maintenance Standards
Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been
removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be
repaired or replaced immediately and visibility restored.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 272
If tree roots have been exposed or injured, "prune"cleanly with an appropriate pruning saw or top-
pers directly above the damaged roots and recover with native soils.Treatment of sap flowing trees
(fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter3-Page 273
BMP C103: High-Visibility Fence
Purpose
High-visibility fencing is intended to:
. Restrict clearing to approved limits.
• Prevent disturbance of sensitive areas,their buffers, and other areas required to be left undis-
turbed.
. Limit construction trafficto designated construction entrances,exits, or internal roads.
. Protect areas where marking with survey tape may not provide adequate protection.
Conditions of Use
To establish clearing limits plastic,fabric,or metal fence may be used:
. At the boundary of sensitive areas,their buffers,and other areas required to be left uncleared.
. As necessary to control vehicle access to and on the site.
Design and Installation Specifications
High-visibility plastic fence shall be composed of a high-density polyethylene material and shall beat
least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center
(maximum)or as needed to ensure rigidity.The fencing shall be fastened to the post every six inches
with a polyethylene tie.On long continuous lengths of fencing, a tension wire or rope shall be used as
a top stringer to prevent sagging between posts.The fence color shall be high-visibility orange.The
fence tensile strength shall be 360 Ibs/ft using the ASTM D4595 testing method.
If appropriate install fabric silt fence in accordance with BMP C233: Silt Fence to act as high-visibility
fence.Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of
this BMP.
Metal fences shall be designed and installed according to the manufacturer's specifications.
Metal fences shall be at least 3 feet high and must be highly visible.
Fences shall not be wired or stapled to trees.
2019 StormwaterManagement Manual for Western Washington
Volume 11-Chapter 3-Page 274
Maintenance Standards
If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and
visibility restored.
BMP C105: Stabilized Construction Access
Purpose
Stabilized construction accesses are established to reduce the amount of sediment transported onto
paved roads outside the project site by vehicles or equipment.This is done by constructing a sta-
bilized pad of quarry spalls at entrances and exits for project sites.
Conditions of Use
Construction accesses shall be stabilized wherever trafficwill be entering or leaving a construction
site if paved roads or other paved areas are within 1,000 feet of the site.
For residential subdivision construction sites, provide a stabilized construction access for each res-
idence, rather than only at the main subdivision entrance.Stabilized surfaces shall be of sufficient
length/width to provide vehicle access/parking, based on lot size and configuration.
On large commercial, highway,and road projects,the designer should include enough extra mater-
ials in the contract to allow for additional stabilized accesses not shown in the initial Construction
SWPPP. It is difficult to determine exactly where access to these projects will take place;additional
materials will enable the contractor to install them where needed.
Design and Installation Specifications
See Figure II-3.1:Stabilized Construction Access for details. Note:the 1 00'minimum length of the
access shall be reduced to the maximum practicable size when the size or configuration of the site
does not allow the full length(100').
Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls,
a 4-inch course of asphalt treated base(ATB), or use existing pavement. Do not use crushed con-
crete,cement,or calcium chloride for construction access stabilization because these products raise
pH levels in stormwater and concrete discharge to waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up
into the rock pad.The geotextile shall meet the standards listed in Table II-3.2:Stabilized Con-
struction Access Geotextile Standards.
Table 11-3.2: Stabilized Construction Access
Geotextile Standards
Geotextile Property Required Value
Grab Tensile Strength(ASTM D4751) 200 psi min.
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Table 11-3.2: Stabilized Construction Access
Geotextile Standards (continued)
Geotextile Property Required Value
Grab Tensile Elongation(ASTM D4632) 30%max.
Mullen Burst Strength(ASTM D3786-80a) 400 psi min.
AOS(ASTM D4751) 20-45(U.S. standard sieve size)
. Consider early installation of the first lift of asphalt in areas that will be paved;this can be used
as a stabilized access.Also consider the installation of excess concrete as a stabilized access.
During large concrete pours,excess concrete is often available for this purpose.
. Fencing(see BMP C103: High-Visibility Fence)shall be installed as necessary to restrict
traffic to the construction access.
. Whenever possible,the access shall be constructed on a firm, compacted subgrade.This can
substantially increase the effectiveness of the pad and reduce the need for maintenance.
. Construction accesses should avoid crossing existing sidewalks and back of walk drains if at
all possible. If a construction access must cross a sidewalk or back of walk drain,the full length
of the sidewalk and back of walk drain must be covered and protected from sediment leaving
the site.
Alternative Material Specification
WSDOT has raised safety concerns about the Quarry Spall rock specified above.WSDOT observes
that the 4-inch to 8-inch rock sizes can become trapped between Dually trucktires,and then
released off-site at highway speeds.WSDOT has chosen to use a modified specification forthe rock
while continuously verifying that the Stabilized Construction Access remains effective.To remain
effective,the BMP must prevent sediment from migrating off site.To date,there has been no per-
formance testing to verify operation of this new specification.Jurisdictions may use the alternative
specification, but must perform increased off-site inspection if they use,or allow others to use, it.
Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand-
ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1)(WSDOT,2016)
for ballast except for the following special requirements.
The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access
Alternative Material Requirements.
Table 11-3.3: Stabilized
Construction Access
Alternative Material
Requirements
Sieve Size Percent Passing
2'/" 99-100
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Table 11-3.3: Stabilized
Construction Access
Alternative Material
Requirements
(continued)
Sieve Size Percent Passing
2" 65-100
3/4" 40-80
No.4 5 max.
No. 100 0-2
% Fracture 75 min.
. All percentages are by weight.
. The sand equivalent value and dust ratio requirements do not apply.
. The fracture requirement shall beat least one fractured face and will apply the combined
aggregate retained on the No.4 sieve in accordance with FOP for AASHTO T 335.
Maintenance Standards
Quarry spalls shall be added if the pad is no longer in accordance with the specifications.
. If the access is not preventing sediment from being tracked onto pavement,then alternative
measures to keep the streets free of sediment shall be used.This may include replace-
ment/cleaning of the existing quarry spalls,street sweeping,an increase in the dimensions of
the access,orthe installation of BMP C106:Wheel Wash.
. Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep-
ing.The sediment collected by sweeping shall be removed or stabilized on site.The pavement
shall not be cleaned by washing down the street,except when high efficiency sweeping is inef-
fective and there is a threat to public safety. If it is necessary to wash the streets,the con-
struction of a small sump to contain the wash water shall be considered.The sediment would
then be washed into the sump where it can be controlled.
. Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high effi-
ciency mechanical sweeper because this creates dust and throws soils into storm systems or
conveyance ditches.
. Any quarry spalls that are loosened from the pad,which end up on the roadway shall be
removed immediately.
. If vehicles are entering or exiting the site at points other than the construction access(es),
BMP C103: High-Visibility Fence shall be installed to control traffic.
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Upon project completion and site stabilization,all construction accesses intended as per-
manent access for maintenance shall be permanently stabilized.
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Figure 11-3.1: Stabilized Construction Access
NOT TO SCALE
R°ad
Ex�s��r9 .-
100'min.
A—
Install driveway
culvert if there is a
roadside ditch present q" 8"quarry
spells
Geotextile
Notes: �15'min.
1. Driveway shall meet 12"minimum thickness
the requirements of the
permitting agency.
2. It is recommended that Provide full width
the access be crowned of ingress/egress r
so that runoff drains off area
the pad.
Stabilized Construction Access
Revised June 2018
DEPARTMENT OF
ECOLOGY Please see httplNuWWecyWa.gov/copyright himl for copyright notice Including permissions,
State of Washington limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume ll-Chapter 3-Page 279
BMP C120: Temporary and Permanent Seeding
Purpose
Seeding reduces erosion by stabilizing exposed soils.A well-established vegetative cover is one of
the most effective methods of reducing erosion.
Conditions of Use
Use seeding throughout the project on disturbed areas that have reached final grade or that will
remain unworked for more than 30 days.
The optimum seeding windows for western Washington are April 1 through June 30 and September
1 through October 1.
Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established.
Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket
until 75 percent grass cover is established.
Review all disturbed areas in late August to early September and complete all seeding by the end of
September.Otherwise,vegetation will not establish itself enough to provide more than average pro-
tection.
Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and
transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding.
See BMP C121: Mulching for specifications.
Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final sta-
bilization means the completion of all soil disturbing activities at the site and the establishment of a
permanent vegetative cover,or equivalent permanent stabilization measures(such as pavement,
riprap,gabions,or geotextiles)which will prevent erosion. See BMP T5.13: Post-Construction Soil
Quality and Depth.
Design and Installation Specifications
General
. Install channels intended for vegetation before starting major earthwork and hydroseed with a
Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control
blankets over the top of hydroseed. Before allowing water to flow in vegetated channels,
establish 75 percent vegetation cover. If vegetated channels cannot be established by seed
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before water flow; install sod in the channel bottom—overtop of hydromulch and erosion con-
trol blankets.
• Confirm the installation of all required surface water control measures to prevent seed from
washing away.
• Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per-
cent tackifier.See BMP C121: Mulching for specifications.
. Areas that will have seeding only and not landscaping may need compostor meal-based
mulch included in the hydroseed in orderto establish vegetation. Re-install native topsoil on
the disturbed soil surface before application.See BMP T5.13: Post-Construction Soil Quality
and Depth.
• When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up
in contact with the soil surface.This reduces the ability to establish a good stand of grass
quickly.To overcome this,consider increasing seed quantities by up to 50 percent.
. Enhance vegetation establishment by dividing the hydromulch operation into two phases:
• Phase 1-Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in
the first lift.
• Phase 2-Install the rest of the mulch and tackifier over the first lift.
Or,enhance vegetation by:
• Installing the mulch,seed,fertilizer,and tackifier in one lift.
• Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per
acre.
• Hold straw in place with a standard tackifier.
Both of these approaches will increase cost moderately but will greatly improve and enhance
vegetative establishment.The increased cost may be offset by the reduced need for:
Irrigation.
Reapplication of mulch.
Repair of failed slope surfaces.
This technique works with standard hydromulch(1,500 pounds per acre minimum)and Bon-
ded Fiber Matrix/Mechanically Bonded Fiber Matrix(BFM/MBFMs)(3,000 pounds per acre
minimum).
. Seed may be installed by hand if:
Temporary and covered by straw, mulch,or topsoil.
Permanent in small areas(usually less than 1 acre) and covered with mulch,topsoil,or
erosion blankets.
. The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include
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recommended mixes for both temporary and permanent seeding.
. Apply these mixes,with the exception of the wet area seed mix,at a rate of 120 pounds per
acre.This rate can be reduced if soil amendments or slow-release fertilizers are used.Apply
the wet area seed mix at a rate of 60 pounds per acre.
. Consult the local suppliers or the local conservation district fortheir recommendations.The
appropriate mix depends on a variety of factors, including location, exposure, soil type,slope,
and expected foot traffic.Alternative seed mixes approved by the local authority may be used,
depending on the soil type and hydrology of the area.
Table 11-3.4: Temporary and Permanent Seed Mixes
Common Name Latin Name % Weight % Purity % Germination
Temporary Erosion Control Seed Mix
A standard mix for areas requiring a temporary vegetative cover.
Chewings or Festuca mbre var.
annual blue grass commutata or Poa 40 98 90
anna
Perennial rye Lolium perenne 50 98 90
Redtop or colonial Agrostis alba or 5 92 85
bentgrass Agrostis tenuis
White dutch clover Tnfolium repens 5 98 90
Landscaping Seed Mix
A recommended mix for landscaping seed.
Perennial rye blend Lolium perenne 70 98 90
Chewings and red Festuca rubm var
fescue blend commutata or Fes- 30 98 90
tuca cobra
Low-Growing Turf Seed Mix
A turf seed mix for dry situations where there is no need for watering.This mix requires very little main-
tenance.
Dwarf tall fescue Festuca amndin- 45 98 90
(several varieties) acea var.
Dwarf perennial Lolium perenne 30 98 90
rye(Barclay) var. barclay
Red fescue Festuca nibra 20 98 90
Colonial bentgrass Agrostis tenuis 5 98 90
Bioswale Seed Mix
A seed mix for bioswales and other intermittently wet areas.
Tall or meadow fes- Festuca amndin- 75-80 98 90
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Table II-3.4: Temporary and Permanent Seed Mixes (continued)
Common Name Latin Name % Weight % Purity % Germination
cue
aces or Festuca
elatior
Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85
Redtop bentgrass Agrostis alba or 5-10 90 80
Agrostis gigantea
Wet Area Seed Mix
A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet-
lands. Consult Hydraulic Permit Authority(HPA)for seed mixes if applicable.
Tall or meadow fes- Festuca arundin-
cue acea or Festuca 60-70 98 90
elatior
Seaside/Creeping Agrostis palustris 10-15 98 85
bentgrass
Meadow(oxtail Sslepocurus praten- 10-15 90 80
Alsike clover Tntolium hybridum 1-6 98 90
Redtop bentgrass Agrostis alba 1-6 92 85
Meadow Seed Mix
A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where col-
onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed-
ing should take place in September or very early October in order to obtain adequate establishment prior to
the winter months.Consider the appropriateness of clover, a fairly invasive species, in the mix.Amending
the soil can reduce the need for clover.
Redtop or Oregon Agrostis alba or
bentgrass Agrostis ore- 20 92 85
gonensis
Red fescue Festuca rubra 70 98 90
White dutch clover Trifolium repens 10 98 90
Roughening and Rototilling
. The seedbed should be firm and rough. Roughen all soil no matterwhatthe slope.Trackwalk
slopes before seeding if engineering purposes require compaction. Backblading or smoothing
of slopes greater than 4H A V is not allowed if they are to be seeded.
• Restoration-based landscape practices require deeper incorporation than that provided by a
simple single-pass rototilling treatment.Wherever practical, initially rip the subgrade to
improve long-term permeability, infiltration, and water inflow qualities.At a minimum,
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permanent areas shall use soil amendments to achieve organic matter and permeability per-
formance defined in engineered soil/landscape systems. For systems that are deeper than 8
inches complete the rototilling process in multiple lifts,or prepare the engineered soil system
per specifications and place to achieve the specified depth.
Fertilizers
• Conducting soil tests to determine the exact type and quantity of fertilizer is recommended.
This will prevent the over-application of fertilizer.
• Organic matter is the most appropriate form of fertilizer because it provides nutrients(includ-
ing nitrogen, phosphorus, and potassium)in the least water-soluble form.
• In general, use 10-4-6 N-P-K(nitrogen-phosphorus-potassium)fertilizer at a rate of 90
pounds per acre.Always use slow-release fertilizers because they are more efficient and
have fewer environmental impacts.Do not add fertilizer to the hydromulch machine,or agit-
ate, more than 20 minutes before use.Too much agitation destroys the slow-release coating.
. There are numerous products available that take the place of chemical fertilizers.These
include several with seaweed extracts that are beneficial to soil microbes and organisms. If
100 percent cottonseed meal is used as the mulch in hydroseed,chemical fertilizer may not be
necessary.Cottonseed meal provides a good source of long-term, slow-release, available
nitrogen.
Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix
• On steep slopes use Bonded Fiber Matrix(BFM)or Mechanically Bonded Fiber Matrix
(MBFM)products.Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre
with approximately 10 percent tackifier.Achieve a minimum of 95 percent soil coverage during
application. Numerous products are available commercially. Most products require 24-36
hours to cure before rainfall and cannot be installed on wet or saturated soils.Generally,
products come in 40-50 pound bags and include all necessary ingredients except for seed and
fertilizer.
I
•
Install products per manufacturer's instructions.
. BFMs and MBFMs provide good alternatives to blankets inmost areas requiring vegetation
establishment.Advantages over blankets include:
BFM and MBFMs do not require surface preparation.
Helicopters can assist in installing BFM and MBFMs in remote areas.
On slopes steeper than 2.5H:1 V, blanket installers may require ropes and harnesses
for safety.
Installing BFM and MBFMs can save at least$1,000 per acre compared to blankets.
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Maintenance Standards
Reseed any seeded areas that fail to establish at least 75 percent cover(100 percent cover for areas
that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such
as sodding, mulching, nets,or blankets.
• Reseed and protect by mulch any areas that experience erosion after achieving adequate
cover. Reseed and protect by mulch any eroded area.
. Supply seeded areas with adequate moisture,but do not water to the extent that it causes run-
off.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP.The products did not
pass through the Technology Assessment Protocol—Ecology(TAPE) process. Local jurisdictions
may choose not to accept these products,or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Gu idance-technical-assistance/Stormwater-per-
mittee-gu idance-resources/Emerging-stormwater-treatment-technologies
BMP C121: Mulching
Purpose
Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant
establishment by conserving moisture, holding fertilizer,seed,and topsoil in place,and moderating
soil temperatures.There are a variety of mulches that can be used.This section discusses only the
most common types of mulch.
Conditions of Use
As a temporary cover measure, mulch should be used:
. For less than 30 days on disturbed areas that require cover.
. At all times for seeded areas, especially during the wet season and during the hot summer
months.
. During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief.
Mulch may be applied at any time of the year and must be refreshed periodically.
For seeded areas, mulch may be made up of 100 percent:
. cottonseed meal;
. fibers made of wood, recycled cellulose, hemp,or kenaf;
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• compost;
. or blends of these.
Tackifier shall be plant-based,such as guar or alpha plantago,or chemical-based such as poly-
acrylamide or polymers.
Generally, mulches come in 40-50 pound bags.Seed and fertilizer are added at time of application.
Recycled cellulose may contain polychlorinated biphenyl(PCBs).Ecology recommends that
products should be evaluated for PCBs priorto use.
Refer to BMP C126: Polyacrylamide(PAM)for Soil Erosion Protection for conditions of use.PAM
shall not be directly applied to water or allowed to enter a water body.
Any mulch or tackifier product used shall be installed per the manufacturer's instructions.
Design and Installation Specifications
For mulch materials,application rates,and specifications,see Table II-3.6: Mulch Standards and
Guidelines.Consult with the local supplier or the local conservation district for their recom-
mendations. Increase the application rate until the ground is 95%covered(i.e. not visible under the
mulch layer). Note:Thickness may be increased for disturbed areas in or near sensitive areas or
other areas highly susceptible to erosion.
Where the option of"Compost"is selected, it should be a coarse compost that meets the size grad-
ations listed in Table II-3.5:Size Gradations of Compost as Mulch Material when tested in accord-
ance with Test Method 02.02-B found in Test Methods forthe Examination of Composting and
Compost(Thompson,2001).
Table 11-3.5: Size Gradations of Compost as Mulch Material
Sieve Size Percent Passing
3" 100%
1" 90%-100%
3/4" 70%-100%
1/4" 40%-100%
Mulch used within the ordinary high-water mark of surface waters should be selected to minimize
potential flotation of organic matter.Composted organic materials have higher specific gravities
(densities)than straw,wood,or chipped material.Consult the Hydraulic Permit Authority(H PA)for
mulch mixes if applicable.
Maintenance Standards
The thickness of the mulch cover must be maintained.
Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the
erosion problem is drainage related,then the problem shall be fixed and the eroded area remulched.
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Table 11-3.6: Mulch Standards and Guidelines
Mulch Mater- Guideline Description
ial
Quality Air-dried;free from undesirable seed and coarse material.
Standards
Ap R plicattesion 2"-3"thick; 5 bales per 1,000 sf or 2-3 tons per acre
Cost-effective protection when applied with adequate thickness. Hand-
application generally requires greater thickness than blown straw.The
Straw 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
Remarks 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. It often introduces and/or encourages the propagation of weed
species and it has no significant long-term benefits It should also not be
used within the ordinary high-water elevation of surface waters(due to flot-
ation).
Quality Standards No growth inhibiting factors.
Application Approx. 35-451bsper1,000sfor1,500-2,000lbsperacre
Hydromulch Rates
Shall be applied with hydromulcher. Shall not be used without seed and
Remarks tackifier unless the application rate is at least doubled. Fibers longer than
about 3/4-1 inch clog hydromulch equipment. Fibers should be kept to less
than 3/4 inch.
Quality No visible water or dust during handling. Must be produced per WAC 173-
Standards 350, Solid Waste Handling Standards, but may have up to 35% biosolids.
Application 2"thick min.; approx. 100 tons per acre(approx.750lbs per cubic yard)
Rates
More effective control can be obtained by increasing thickness to 3". Excel-
Compost lent mulch for protecting final grades until landscaping because it can be dir-
ectly seeded or tilled into soil as an amendment. Compost used for mulch
Remarks has a coarser size gradation than compost used for BMP C 125:Topsoiling
/Composting or BMP T5.13: Post-Construction Soil Quality and Depth. It
is more stable and practical to use in wet areas and during rainy weather
conditions. Do not use near wetlands or near phosphorous impaired water
bodies.
Quality Gradations from fines to 6 inches in length for texture,variation, and inter-
Chipped Standards locking properties. Include a mix of various sizes so that the average size
Site Veget- is between 2-and 4-inches.
ation Application
2"thick min.;
Rates
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Table 11-3.6: Mulch Standards and Guidelines (continued)
Mulch Mater-
ial Guideline Description
This is a cost-effective way to dispose of debris from clearing and grub-
bing, 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 Sur-
Remarks face waters. If permanent seeding or planting is expected shortly after
mulch,the decomposition of the chipped vegetation may tie up nutrients
important to grass establishment.
Note:thick application of this material over existing grass, herbaceous spe-
cies, and some groundcovers could smother and kill vegetation.
Quality No visible water or dust during handling. Must be purchased from a supplier
Standards with a Solid Waste Handling Permit or one exempt from solid waste reg-
ulations.
Application 2"thick min.; approx. 100 tons per acre(approx.750lbs. per cubic yard)
Wood- Rates
Based This material is often called"wood straw"or"hog fuel'.The use of mulch
Mulch ultimately improves the organic matter in the soil. Special caution is
Remarks advised regarding the source and composition of wood-based mulches. Its
preparation typically does not provide any weed seed control,so evidence
of residual vegetation in its composition or known inclusion of weed plants
or seeds should be monitored and prevented(or minimized).
Quality A blend of loose, long,thin wood pieces derived from native conifer or
Standards deciduous trees with high length-to-width ratio.
Application 2"thick min.
Rates
Wood Cost-effective protection when applied with adequate thickness.A min-
Strand imum of 95-percent of the wood strand shall have lengths between 2 and
Mulch 10-inches,with a width and thickness between 1/16 and 1/2-inches.The
Remarks mulch shall not contain resin,tannin, or other compounds in quantities that
would be detrimental to plant life. Sawdust or wood shavings shall not be
used as mulch. [Specification 9-14.4(4)from the Standard Specifications
for Road, Bndge, andMunicipalConstructionDW T,2016)
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BMP C125: Topsoiling / Composting
Purpose
Topsoiling and composting provide a suitable growth medium for final site stabilization with veget-
ation.While not a permanent cover practice in itself,topsoiling and composting are an integral com-
ponent of providing permanent cover in those areas where there is an unsuitable soil surface for
plant growth. Use this BMP in conjunction with other BMPs such as BMP C120:Temporary and Per-
manent Seeding, BMP C121:Mulching,or BMP C124: Sodding. Implementation of this BMP may
meet the post-construction requirements of BMP T5.13: Post-Construction Soil Quality and Depth.
Native soils and disturbed soils that have been organically amended not only retain much more
stormwater,but also serve as effective biofilters for urban pollutants and,by supporting more vig-
orous plant growth, reduce the water,fertilizer and pesticides needed to support installed land-
scapes.Topsoil does not include any subsoils but only the material from the top several inches
including organic debris.
Conditions of Use
• Permanent landscaped areas shall contain healthy topsoil that reduces the need for fertilizers,
improves overall topsoil quality,provides for better vegetative health and vitality, improves
hydrologic characteristics,and reduces the need for irrigation.
. Leave native soils and the duff layer undisturbed to the maximum extent practicable.Stripping
of existing, properly functioning soil system and vegetation for the purpose of topsoiling during
construction is not acceptable. Presence existing soil systems in undisturbed and uncom-
pacted conditions if functioning properly.
. Areas that already have good topsoil, such as undisturbed areas,do not require soil amend-
ments.
• Restore,to the maximum extent practical, native soils disturbed during clearing and grading to
a condition equal to or better than the original site condition's moisture-holding capacity. Use
on-site native topsoil, incorporate amendments into on-site soil,or import blended topsoil to
meet this requirement.
. Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of
critically low pH (high acid)levels.
• Beware of where the topsoil comes from,and what vegetation was on site before disturbance.
Invasive plant seeds may be included and could cause problems for establishing native plants,
landscaped areas,or grasses.
. Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root
growth and nutrient transfer.These native mycorrhiza are acclimated to the site and will
provide optimum conditions for establishing grasses. Use commercially available mycorrhiza
products when using off-site topsoil.
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Design and Installation Specifications
Meet the following requirements for disturbed areas that will be developed as lawn or landscaped
areas at the completed project site:
• Maximize the depth of the topsoil wherever possible to provide the maximum possible infilt-
ration capacity and beneficial growth medium.Topsoil shall have:
• A minimum depth of 8-inches.Scarify subsoils below the topsoil layer at least 4-inches
with some incorporation of the upper material to avoid stratified layers,where feasible.
Ripping or re-structuring the subgrade may also provide additional benefits regarding
the overall infiltration and interflow dynamics of the soil system.
• A minimum organic content of 10%dry weight in planting beds,and 5%organic matter
content in turf areas. Incorporate organic amendmentsto a minimum 8-inch depth
except where tree roots or other natural features limit the depth of incorporation.
• A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil.
• If blended topsoil is imported,then fines should be limited to 25 percent passing through
a 200 sieve.
• Mulch planting beds with 2 inches of organic material
. Accomplish the required organic content, depth,and pH by returning native topsoil to the site,
importing topsoil of sufficient organic content,and/or incorporating organic amendments.
When using the option of incorporating amendments to meet the organic content requirement,
use compost that meets the compost specification for Bioretention(See BMP T7.30:Biore-
tention),with the exception that the compost may have up to 35%biosolids or manure.
. Sections 3 through 7 of Building Soil:Guidelines and Resources for Implementing Soil Quality
and Depth BMP T5.13 in WDOE Stormwater Management Manual for Western Washington
(Stenn et al.,2016),provides useful guidance for implementing whichever option is chosen. It
includes guidance for pre-approved default strategies and guidance for custom strategies.
Check with your local jurisdiction concerning its acceptance of this guidance.
. The final composition and construction of the soil system will result in a natural selection or
favoring of certain plant species over time. For example, incorporation of topsoil may favor
grasses,while layering with mildly acidic, high-carbon amendments may favor more woody
vegetation.
. Allow sufficient time in scheduling for topsoil spreading prior to seeding,sodding, or planting.
. Take care when applying top soil to subsoils with contrasting textures.Sandy topsoil over
clayey subsoil is a particularly poor combination, as water creeps along the junction between
the soil layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded,
water will not infiltrate the soil profile evenly and it will be difficult to establish vegetation.The
best method to promote bonding is to actually work the topsoil into the layer below for a depth
of at least 6 inches.
. Field exploration of the site shall be made to determine if there is surface soil of sufficient
quantity and quality to justify stripping.Topsoil shall be friable and loamy(loam,sandy loam,
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silt loam,sandy clay loam,and clay loam).Avoid areas of natural ground water recharge.
. Stripping shall be confined to the immediate construction area.A 4-inch to 6-inch stripping
depth is common,but depth may vary depending on the particular soil.All surface runoff con-
trol structures shall be in place prior to stripping.
. Do not place topsoil while in a frozen or muddy condition,when the subgrade is excessively
wet,or when conditions exist that may otherwise be detrimental to proper grading or pro-
posed sodding or seeding.
. In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a des-
ignated, controlled area, not adjacent to public resources and critical areas.Reapply stock-
piled topsoil to other portions of the sitewhere feasible.
. Locate the topsoil stockpile so that it meets specifications and does not interfere with work on
the site. It may be possible to locate more than one pile in proximity to areas where topsoil will
be used.
. Stockpiling of topsoil shall occur in the following manner:
Side slopes of the stockpile shall not exceed 2H:1 V.
Between October 1 and April 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil.
■ Within 2 days complete erosion control seeding,or covering stockpiles with clear
plastic,or other mulching materials.
Between May 1 and September 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil if the
stockpile will remain in place for a longer period of time than active construction
grading.
■ Within 7 days complete erosion control seeding,or covering stockpiles with clear
plastic,or other mulching materials.
• When native topsoil is to be stockpiled and reused the following should apply to ensure that
the mycorrhizal bacterial,earthworms,and other beneficial organisms will not be destroyed:
• Re-install topsoil within 4 to 6 weeks.
• Do not allow the saturation of topsoil with water.
• Do not use plastic covering.
Maintenance Standards
• Inspect stockpiles regularly,especially after large storm events. Stabilize any areas that have
eroded.
• Establish soil quality and depth toward the end of construction and once established, protect
from compaction,such as from large machinery use,and from erosion.
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• Plant and mulch soil after installation.
• Leave plant debris or its equivalent on the soil surface to replenish organic matter.
• Reduce and adjust,where possible,the use of irrigation,fertilizers,herbicides and pesticides,
rather than continuing to implement formerly established practices.
Il.
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BMP C140: Dust Control
Purpose
Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways,drainage
ways, and surface waters.
Conditions of Use
Use dust control in areas(including roadways)subject to surface and air movement of dust where
on-site or off-site impacts to roadways,drainage ways, or surface waters are likely.
Design and Installation Specifications
. Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching,
or paving is impractical,apply gravel or landscaping rock.
• Limit dust generation by clearing only those areas where immediate activity will take place,
leaving the remaining area(s)in the original condition. Maintain the original ground cover as
long as practical.
• Construct natural or artificial windbreaks or windscreens.These may be designed as enclos-
ures for small dust sources.
. Sprinkle the site with water until the surface is wet. Repeat as needed.To prevent carryout of
mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106:
Wheel Wash.
• Irrigation water can be used for dust control. Irrigation systems should be installed as a first
step on sites where dust control is a concern.
. Spray exposed soil areas with a dust palliative,following the manufacturer's instructions and
cautions regarding handling and application. Used oil is prohibited from use as a dust sup-
pressant.Local governments may approve other dust palliatives such as calcium chloride or
PAM.
• PAM(BMP C126: Polyacrylamide(PAM)for Soil Erosion Protection)added to water at a rate
of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effect-
ive than water alone.This is due to increased infiltration of water into the soil and reduced
evaporation. In addition,small soil particles are bonded together and are not as easily trans-
ported by wind.Adding PAM may reduce the quantity of water needed for dust control. Note
that the application rate specified here applies to this BMP,and is not the same application
rate that is specified in BMP C126: Polyacrylamide(PAM)for Soil Erosion Protection,but the
downstream protections still apply.
Refer to BMP C126:Polyacrylamide(PAM)for Soil Erosion Protection for conditions of use.
PAM shall not be directly applied to water or allowed to enter a water body.
• Contact your local Air Pollution Control Authority for guidance and training on other dust con-
trol measures.Compliance with the local Air Pollution Control Authority constitutes
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compliance with this BMP.
• Use vacuum street sweepers.
. Remove mud and other dirt promptly so it does not dry and then turn into dust.
. Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust stirred up from
unpaved roads and lots.
• Upgrade the road surface strength by improving particle size,shape,and mineral types
that make up the surface and base materials.
• I
Add surface gravel to reduce the source of dust emission. Limit the amount of fine
particles(those smaller than.075 mm)to 10 to 20 percent.
• Use geotextile fabrics to increase the strength of new roads or roads undergoing recon-
struction.
• Encourage the use of alternate, paved routes, if available.
• Apply chemical dust suppressants using the admix method, blending the product with
the top few inches of surface material.Suppressants may also be applied as surface
treatments.
• Limit dust-causing work on windy days.
• Pave unpaved permanent roads and othertrafficked areas.
Maintenance Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose
Keep quantities of erosion prevention and sediment control materials on the project site at all times
to be used for regular maintenance and emergency situations such as unexpected heavy rains. Hav-
ing these materials on-site reduces the time needed to replace existing or implement new BMPs
when inspections indicate that existing BMPs are not meeting the Construction SWPPP require-
ments. In addition,contractors can save money by buying some materials in bulk and storing them at
their office or yard.
Conditions of Use
. Construction projects of any size or type can benefit from having materials on hand.A small
commercial development project could have a roll of plastic and some gravel available for
immediate protection of bare soil and temporary berm construction.A large earthwork project,
such as highway construction, might have several tons of straw,several rolls of plastic,flexible
2019 Stormwater Management Manual for Western Washington
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pipe, sandbags,geotextile fabric and steel"T'posts.
• Materials should be stockpiled and readily available before any site clearing, grubbing,or
earthwork begins.A large contractor or project proponent could keep a stockpile of materials
that are available for use on several projects.
• If storage space at the project site is at a premium,the contractor could maintain the materials
at their office or yard. The office or yard must be less than an hour from the project site.
Design and Installation Specifications
Depending on project type,size, complexity,and length, materials and quantities will vary.A good
minimum list of items that will cover numerous situations includes:
. Clear Plastic,6 mil
• Drainpipe, 6 or 8 inch diameter
• Sandbags,filled
• Straw Bales for mulching
. Quarry Spalls
• Washed Gravel
• Geotextile Fabric
• Catch Basin Inserts
• Steel"T Posts
• Silt fence material
• Straw Wattles
Maintenance Standards
. All materials with the exception of the quarry spalls, steel"T'posts, and gravel should be kept
covered and out of both sun and rain.
• Re-stock materials as needed.
BMP C151 : Concrete Handling
Purpose
Concrete work can generate process water and slurry that contain fine particles and high pH, both of
which can violate water quality standards in the receiving water. Concrete spillage or concrete dis-
charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete,con-
crete process water, and concrete slurry from entering waters of the State.
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Conditions of Use
Any time concrete is used, utilize these management practices. Concrete construction project com-
ponents include, but are not limited to:
. Curbs
. Sidewalks
• Roads
• Bridges
• Foundations
• Floors
• Runways
Disposal options for concrete, in order of preference are:
1. Off-site disposal
2. Concrete wash-out areas(see BMP C154: Concrete Washout Area)
3. De min imus washout to formed areas awaiting concrete
Design and Installation Specifications
• Wash concrete truck drums at an approved off-site location or in designated concrete
washout areas only. Do not wash out concrete trucks onto the ground (including formed areas
awaiting concrete),or into storm drains,open ditches, streets,or streams.Refer to BMP
C154:Concrete Washout Area for information on concrete washout areas.
Return unused concrete remaining in the truck and pump to the originating batch plant
for recycling. Do not dump excess concrete on site, except in designated concrete
washout areas as allowed in BMP C154: Concrete Washout Area.
. Wash small concrete handling equipment(e.g.hand tools, screeds, shovels, rakes,floats,
trowels, and wheelbarrows)into designated concrete washout areas or into formed areas
awaiting concrete pour.
. At no time shall concrete be washed off into the footprint of an area where an infiltration fea-
ture will be installed.
. Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir-
ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.
• Do not allow washwater from areas,such as concrete aggregate driveways,to drain directly
(without detention or treatment)to natural or constructed stormwater conveyances.
. Contain washwater and leftover product in a lined container when no designated concrete
washout areas(or formed areas,allowed as described above)are available. Dispose of con-
tained concrete and concrete washwater(process water)properly.
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. Always use forms or solid barriers for concrete pours,such as pilings,within 15-feet of surface
waters.
• Refer to BMP C252:Treating and Disposing of High pH Water for pH adjustment require-
ments.
• Refer to the Construction Stormwater General Permit(CSWGP)for pH monitoring require-
ments if the project involves one of the following activities:
Significant concrete work(as defined in the CSWGP).
The use of soils amended with (but not limited to)Portland cement-treated base,
cement kiln dust or fly ash.
Discharging stormwater to segments of water bodies on the 303(d)list(Category 5)for
high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and repair the same day.
BMP C152: Sawcutting and Surfacing Pollution
Prevention
Purpose
Sawcutting and surfacing operations generate slurry and processwater that contains fine particles
and high pH (concrete cutting), both of which can violate the water quality standards in the receiving
water.Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to
minimize and eliminate process water and slurry created through sawcutting or surfacing from enter-
ing waters of the State.
Conditions of Use
Utilize these management practices anytime sawcutting or surfacing operations take place. Saw-
cutting and surfacing operations include, but are not limited to:
. Sawing
• Coring
• Grinding
. Roughening
. Hydro-demolition
. Bridge and road surfacing
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Design and Installation Specifications
• Vacuum slurry and cuttings during cutting and surfacing operations.
. Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.
. Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ-
ing stormwater systems.This may require temporarily blocking catch basins.
. Dispose of collected slurry and cuttings in a mannerthat does not violate ground water or sur-
face water quality standards.
• Do not allow process water generated during hydro-demolition,surface roughening or similar
operations to drain to any natural or constructed drainage conveyance including stormwater
systems. Dispose of process water in a manner that does not violate ground water or surface
water quality standards.
• Handle and dispose of cleaning waste material and demolition debris in a manner that does
not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an
appropriate disposal site.
Maintenance Standards
Continually monitor operations to determine whether slurry,cuttings,or process water could enter
waters of the state. If inspections show that a violation of water quality standards could occur,stop
operations and immediately implement preventive measures such as berms, barriers,secondary
containment,and/or vacuum trucks.
BMP C153: Material Delivery, Storage, and
Containment
Purpose
Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses
from material delivery and storage. Minimize the storage of hazardous materials on-site, store mater-
ials in a designated area,and install secondary containment.
Conditions of Use
Use at construction sites with delivery and storage of the following materials:
• Petroleum products such as fuel, oil and grease
. Soil stabilizers and binders(e.g., Polyacrylamide)
• Fertilizers, pesticides and herbicides
• Detergents
. Asphalt and concrete compounds
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• Hazardous chemicals such as acids,lime,adhesives,paints,solvents, and curing compounds
. Any other material that maybe detrimental if released to the environment
Design and Installation Specifications
. The temporary storage area should be located away from vehicular traffic, near the con-
struction entrance(s),and away from waterways or storm drains.
• Safety Data Sheets(SDS)should be supplied for all materials stored.Chemicals should be
kept in their original labeled containers.
. Hazardous material storage on-site should be minimized.
• Hazardous materials should be handled as infrequently as possible.
• During the wetweather season(Oct 1 —April 30),consider storing materials in a covered
area.
• Materials should be stored in secondary containments,such as an earthen dike, horse trough,
or even a children's wading pool for non-reactive materials such as detergents,oil,grease,
and paints.Small amounts of material may be secondarily contained in"bus boy"trays or con-
crete mixing trays.
• Do not store chemicals, drums,or bagged materials directly on the ground. Place these items
on a pallet and,when possible,within secondary containment.
. If drums must be kept uncovered,store them at a slight angle to reduce ponding of rainwater
on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of
drums, preventing water from collecting.
. Liquids, petroleum products,and substances listed in 40 CFR Parts 110, 117, or 302 shall be
stored in approved containers and drums and shall not be overfilled, Containers and drums
shall be stored in temporary secondary containment facilities.
. Temporary secondary containment facilities shall provide for a spill containment volume able
to contain 10%of the total enclosed container volume of all containers,or 110%of the capa-
city of the largest container within its boundary,whichever is greater.
. Secondary containment facilities shall be impervious to the materials stored therein for a min-
imum contact time of 72 hours.
. Sufficient separation should be provided between stored containers to allow for spill cleanup
and emergency response access.
• During the wet weather season (Oct 1 —April 30),each secondary containment facility shall
be covered during non-working days, prior to and during rain events.
• Keep material storage areas clean,organized and equipped with an ample supply of appro-
priate spill clean-up material(spill kit).
. The spill kit should include, at a minimum:
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1-Water Resistant Nylon Bag
3-Oil Absorbent Socks 3"x 4'
2-Oil Absorbent Socks 3"x 10'
12-Oil Absorbent Pads 17"x19"
1-Pair Splash Resistant Goggles
3-Pair Nitrile Gloves
10-Disposable Bags with Ties
Instructions
Maintenance Standards
. Secondary containment facilities shall be maintained free of accumulated rainwater and spills.
In the event of spills or leaks,accumulated rainwater and spills shall be collected and placed
into drums.These liquids shall be handled as hazardous waste unless testing determines
them to be non-hazardous.
• Re-stock spill kit materials as needed.
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BMP C162: Scheduling
Purpose
Sequencing a construction project reduces the amount and duration of soil exposed to erosion by
wind, rain, runoff, and vehicle tracking.
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Volume 11-Chapter 3-Page 328
Conditions of Use
The construction sequence schedule is an orderly listing of all major land-disturbing activities
togetherwith the necessary erosion and sedimentation control measures planned for the project.
This type of schedule guides the contractor on work to be done before otherwork is started so that
serious erosion and sedimentation problems can be avoided.
Following a specified work schedule that coordinates the timing of land-disturbing activities and the
installation of control measures is perhaps the most cost-effective way of controlling erosion during
construction.The removal of ground cover leaves a site vulnerable to erosion.Construction sequen-
cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and
restores protective cover quickly can significantly reduce the erosion potential of a site.
Design Considerations
• Minimize construction during rainy periods.
. Schedule projects to disturb only small portions of the site at anyone time.Complete grading
as soon as possible. Immediately stabilize the disturbed portion before grading the next por-
tion. Practice staged seeding in order to revegetate cut and fill slopes asthe work progresses.
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BMP C220: Inlet Protection
Purpose
Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta-
bilization of the disturbed area.
Conditions of Use
Use inlet protection at inlets that are operational before permanent stabilization of the disturbed
areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and
within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment
trapping BMP.
Also consider inlet protection for lawn and yard drains on new home construction.These small and
numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof
drain system. If possible,delay installing lawn and yard drains untiljust before landscaping,or cap
these drains to prevent sediment from entering the system until completion of landscaping. Provide
18-inches of sod around each finished lawn and yard drain.
Table II-3.10:Storm Drain Inlet Protection lists several options for inlet protection.All of the methods
for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain-
age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with
additional end-of-pipe treatment where stormwater ponding would cause a hazard.
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Table 11-3.10: Storm Drain Inlet Protection
tion Overflow Paved/ Earthen Sur- Conditions of Use
tec
faces
Type of Inlet Pro- Emergency Applicable for
Drop Inlet Protection
Excavated drop Yes,temporary Applicable for heavy flows. Easy
inlet protection flooding may Earthen to maintain. Large area requirement:
occur 30'x30'/acre
Block and gravel Applicable for heavy concentrated flows.
drop inlet pro- Yes Paved or Earthen Will not pond.
tection
Gravel and wire
drop inlet pro- No Paved or Earthen Applicable for heavy concentrated flows.
tection Will pond. Can withstand traffic.
Catch basin filters Yes Paved or Earthen Frequent maintenance required.
Curb Inlet Protection
Curb inlet pro-
tectionSmall capacity Used for sturdy, more compact install-
wooden we overflow Paved ation.
wooden weir
Block and gravel
curb inlet pro- Yes Paved Sturdy, but limited filtration.
tection
Culvert Inlet Protection
Culvert inlet sed- N/A N/A 1 B month expected life.
iment trap
Design and Installation Specifications
Excavated Drop Inlet Protection
Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet.
Sediment settles out of the stormwater prior to entering the storm drain.Design and installation spe-
cifications for excavated drop inlet protection include:
. Provide a depth of 1-2 ft as measured from the crest of the inlet structure.
. Slope sides of excavation should be no steeper than 2H:1 V.
• Minimum volume of excavation is 35 cubic yards.
. Shape the excavation to fit the site,with the longest dimension oriented toward the longest
inflow area.
• Install provisions for draining to prevent standing water.
. Clear the area of all debris.
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. Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
. Protect weep holes with screen wire and washed aggregate.
. Seal weep holes when removing structure and stabilizing area.
. Build a temporary dike, if necessary,to the down slope side of the structure to prevent bypass
flow.
Block and Gravel Filter
A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel.
See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil-
ters include:
• Provide a height of 1 to 2 feet above the inlet.
. Recess the first row of blocks 2-inches into the ground for stability.
. Support subsequent courses by placing a pressure treated wood 2x4 through the block open-
ing.
• Do not use mortar.
• Lay some blocks in the bottom row on their side to allow for dewatering the pool.
. Place hardware cloth or comparable wire mesh with openings over all block openings.
• Place gravel to just below the top of blocks on slopes of 2H:1 V or flatter.
. An alternative design is a gravel berm surrounding the inlet,as follows:
• Provide a slope of 3H:1 V on the upstream side of the berm.
o Provide a slope of 2H:1 V on the downstream side of the berm.
• Provide a 1-foot wide level stone area between the gravel berm and the inlet.
• Use stones 3 inches in diameter or larger on the upstream slope of the berm.
• Use gravel'/r to at a minimum thickness of 1-foot on the downstream slope of
the berm.
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li
Figure II-3.17: Block and Gravel Filter
A
Drain grate Qo
o�^�'pO��o•00 600 o���F9
�° aC/� O� O: 1Om so Opoo'p
o0.-0 '•O o��� fJ°��a Concrete block
a p
,U�pogoa
Qe °
Oo Gravel backfill
.�a°ao�a 000000 o�oQo
4:b °
o�YMo
0o p ° o
o °Q o0 0
��Q"O
�o� mo<Do
yero� o�o�O���o4i0o���`�oa°o
�y A
Plan View
Concrete block
Wire screen or
fitter fabric
Gravel backfll _ Overflow
o water o bPonnding height
�O a� Water
Section A-A
Notes:
1. Drop inlet sediment barriers are to be used for small,nearly level drainage areas.(less
than 5%)
2. Excavate a basin of sufficient size adjacent to the drop inlet.
3. The top of the structure(pending height)must be well below the ground elevation
downslope to prevent runoff from bypassing the inlet.A temporary dike may be
necessary on the downslope side of the structure.
NOT TO SCALE
rl�
Block and Gravel Filter
Revised June 2016
DEPARTMENT OF
ECOLOGY Please see httin.,1Awecy.wa.gov/copyright.himl for copyright notice including permissions.
State.of Washington limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume II-Chapter 3-Page 359
Gravel and Wire Mesh Filter
Gravel and wire mesh filters are gravel barriers placed overthe top of the inlet.This method does not
provide an overflow. Design and installation specifications for gravel and wire mesh filters include:
. Use a hardware cloth or comparable wire mesh with openings.
Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey-
ond each side of the inlet structure.
Overlap the strips if more than one strip of mesh is necessary.
• Place coarse aggregate over the wire mesh.
o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at
least 18-inches on all sides.
Catch Basin Filters
Catch basin filters are designed by manufacturers for construction sites.The limited sediment stor-
age capacity increases the amount of inspection and maintenance required,which may be daily for
heavy sediment loads.To reduce maintenance requirements, combine a catch basin filter with
another type of inlet protection.This type of inlet protection provides flow bypasswithout overflow
and therefore may be a better method for inlets located along active rights-of-way. Design and install-
ation specifications for catch basin filters include:
. Provides 5 cubic feet of storage.
. Requires dewatering provisions.
. Provides a high-flow bypass that will not clog under normal use at a construction site.
. Insert the catch basin filter in the catch basin just below the grating.
Curb Inlet Protection with Wooden Weir
Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb
inletwith a wooden frame and gravel. Design and installation specifications for curb inlet protection
with wooden weirs include:
. Use wire mesh with'/rinch openings.
• Use extra strength filter cloth.
. Construct a frame.
. Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against the wire and fabric.
. Place weight on the frame anchors.
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Block and Gravel Curb Inlet Protection
Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and
gravel. See Figure II-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe-
cifications for block and gravel curb inlet protection include:
• Use wire mesh with'/rinch openings.
• Place two concrete blocks on their sides abutting the curb at either side of the inlet opening.
These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.
. Place blocks on their sides across the front of the inlet and abutting the spacer blocks.
. Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
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Figure II-3.18: Block and Gravel Curb Inlet Protection
A
Catch basin
Back of sidewalk
2x4 Wood stud
Back of curb Curb role} Concrete block
4e �8 ngaro n°
Wire screen or �
filterfabric
a/a inch(20 mm) Concrete block
Drain gravel Plan View
Pending height
3/a inch(20 mm)
Drain gravel Overflow
Curb inlet �j
Wire screen or \��/° �/ /"
filterfabric 2x4 Wood stud �'\�' iS. M,
(100x50 Timber stud)
Catch basin
Concrete block
Section A-A
Notes:
1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street
segment,where water can pond and allow sediment to separate from runoff.
2. Barrier shall allow for overflow from severe storm event.
3. Inspect barriers and remove sediment after each stone event.Sediment and gravel must be
removed from the traveled way immediately. NOT TO SCALE
rr�
Block and Gravel Curb Inlet Protection
Revised June 2016
DEPARTMENT OF
ECOLOGY Please see http.,IAvw v.e y.wa.govlcopyright.html for copyright notice including permissions,
State of Washington limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 362
Curb and Gutter Sediment Barrier
Curb and gutter sediment barrier is a sandbag or rock berm(riprap and aggregate)3 feet high and 3
feetwide in a horseshoe shape.See Figure II-3.19:Curb and Gutter Barrier. Design and installation
specifications for curb and gutter sediment barrier include:
. Construct a horseshoe shaped berm,faced with coarse aggregate if using riprap,3 feet high
and 3 feet wide,at least 2 feet from the inlet.
. Construct a horseshoe shaped sedimentation trap on the upstream side of the berm.Size the
trap to sediment trap standards for protecting a culvert inlet.
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Figure II-3.19: Curb and Gutter Barrier
Back of sidewalk
Burlap sacks to
overlap onto curb Back of curb
Curb inlet
Runoff
Runoff Spillway
Catch basin
Plan View
Gravel filled sandbags
stacked tightly
Notes:
1. Place curb type sediment barriers on gently sloping street segments,where water can
pond and allow sediment to separate from runoff.
2. Sandbags of either burlap or woven'geotextile'fabric,are filled with gravel,layered
and packed tightly.
3. Leave a one sandbag gap in the top row to provide a spillway for overflow.
4. Inspect barriers and remove sediment after each storm event.Sediment and gravel
must be removed from the traveled way immediately. NOT TO SCALE
FDEPARTIMENT
Curb and Gutter Barrier
MOM Revised June 2016
Please see http.,IA w..ecywa.gov/copyrlghthtml for copyright notice including permissions,
limitation of liability,and disclaimer.
2019 StormwaterManagement Manual for Western Washington
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Maintenance Standards
. Inspect all forms of inlet protection frequently,especially after storm events.Clean and
replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the
inlet and clean or replace.An alternative approach would be to use the clogged rock as fill and
put fresh rock around the inlet.
. Do not wash sediment into storm drains while cleaning.Spread all excavated material evenly
over the surrounding land area or stockpile and stabilize as appropriate.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP.The products did not
pass through the Technology Assessment Protocol—Ecology(TAPE)process. Local jurisdictions
may choose not to accept these products,or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/E merging-stormwater-treatment-technologies
2019 Stormwater Management Manual for Western Washington
Volume It-Chapter 3-Page 365
BMP C233: Silt Fence
Purpose
Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary
physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
Silt fence maybe used downslope of all disturbed areas.
. Silt fence shall prevent sediment carried by runoff from going beneath,through,or over the
top of the silt fence, but shall allow the water to pass through the fence.
. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial
amounts of overland flow.Convey any concentrated flows through the drainage system to a
sediment trapping BMP.
• Do not construct silt fences in streams or use in V-shaped ditches.Silt fences do not provide
an adequate method of silt control for anything deeper than sheet or overland flow.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter3-Page 370
Figure 11-3.22: Silt Fence
Joints in geotextile fabric shall be
spliced at posts.Use staples,wire rings
or equivalent to attach fabric to posts
TNT'by 14 Ga.wire or equivalent,
if standard strength fabric used
I
I
I
Minimum J 6'max
4"x4"trench I
u
Post spacing may be increased
to 8'if wire backing is used 2"x2"wood posts,steel
fence posts,or equivalent
2"x2"by 14 Ga.wire or equivalent,
if standard strength fabric used
Oeoiexlile fabric
2'min
Backflll trench with
native soil or 3/"-
1.5"washed gravel V�12"minVAAV�A�VA `��
Minimum
4"x4"trench /�\�
2N2"wood posts,steel
fence posts,or equivalent NOT TO SCALE
rl�
Silt Fence
Revised July 2017
DEPARTMENT OF
ECOLOGY please see http./Mnvvv.ecy.wa.gov/copWghthtml for copyright notice including permissions,
State of Washington limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 371
Design and Installation g Specifications
�i
•
Use in combination with other construction stormwater BMPs.
. Maximum slope steepness(perpendicular to the silt fence line) 1 HA V,
- Maximum sheet or overland flow path length to the silt fence of 100 feet.
. Do not allow flows greater than 0.5 cfs.
. Use geotextile fabric that meets the following standards.All geotextile properties listed below
are minimum average roll values(i.e.,the test result for any sampled roll in a lot shall meet or
exceed the values shown in Table II-3.11:Geotextile Fabric Standards for Silt Fence):
Table 11-3.11: Geotextile Fabric Standards for Silt Fence
Geotextile Property Minimum Average Roll Value
Polymeric Mesh AOS 0.60 mm maximum forslit film woven(#30 sieve).
(ASTM D4751) 0.30 mm maximum forall othergeotextile types(#50 sieve).
0.15 mm minimum for all fabric types(#100 sieve).
Water Permittivity 0.02sec-1 minimum
(ASTM D4491)
Grab Tensile Strength 180lbs. Minimum for extra strength fabric.
(ASTM D4632) 100lbs minimum for standard strength fabric.
Grab Tensile Strength o
30/o maximum
(ASTM D4632)
Ultraviolet Resistance
(ASTM D4355) 70% minimum
. Support standard strength geotextiles with wire mesh,chicken wire,2-inch x 2-inch wire,
safetyfence,orjute mesh to increase the strength of the geotextile. Siltfence materials are
available that have synthetic mesh backing attached.
• Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum
of six months of expected usable construction life at a temperature range of 00F to 120°F.
• One-hundred percent biodegradable silt fence is available that is strong,long lasting, and can
be left in place after the project is completed, if permitted by the local jurisdiction.
. Refer to Figure II-3.22:Silt Fence for standard silt fence details. Include the following Stand-
ard Notes for silt fence on construction plans and specifications:
1. The Contractor shall install and maintain temporary silt fences at the locations shown in
the Plans.
2. Construct silt fences in areas of clearing,grading, or drainage prior to starting those
activities.
2019 Stormwater Management Manual for Western Washington
Volume II-Chapter 3-Page 372
3. The silt fence shall have a 2-feet min.and a 2'/2-feet max.height above the original
ground surface.
4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric
lengths as required. Locate all sewn seams at support posts.Alternatively,two sections
of silt fence can be overlapped, provided that the overlap is long enough and that the
adjacent silt fence sections are close enough together to prevent silt laden water from
escaping through the fence at the overlap.
5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples,
wire, or in accordance with the manufacturer's recommendations.Attach the geotextile
fabric to the posts in a manner that reduces the potential for tearing.
6. Support the geotextile fabric with wire or plastic mesh,dependent on the properties of
the geotextile selected for use. If wire or plastic mesh is used,fasten the mesh securely
to the up-slope side of the posts with the geotextile fabric up-slope of the mesh.
7. Mesh support, if used,shall consist of steel wire with a maximum mesh spacing of 2-
inches,or a prefabricated polymeric mesh.The strength of the wire or polymeric mesh
shall be equivalent to or greater than 180lbs.grab tensile strength.The polymeric mesh
must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it
supports.
8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill
and tamp soil in place over the buried portion of the geotextile fabric,so that no flow can
pass beneath the silt fence and scouring cannot occur.When wire or polymeric back-up
support mesh is used,the wire or polymeric mesh shall extend into the ground 3-inches
min.
9. Drive or place the siltfence posts into the ground 18-inches min.A 12—inch min.depth
is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be
reached. Increase fence post min.depths by 6 inches if the fence is located on slopes of
3H:1 V or steeper and the slope is perpendicular to the fence. If required post depths
cannot be obtained,the posts shall be adequately secured by bracing or guying to pre-
vent overturning of the fence due to sediment loading.
10. Use wood,steel or equivalent posts.The spacing of the support posts shall be a max-
imum of 6-feet. Posts shall consist of either:
. Wood with minimum dimensions of 2 inches by 2 inches by 3 feet.Wood shall be
free of defects such as knots,splits,or gouges.
• No.6 steel rebar or larger.
. ASTM A 120 steel pipe with a minimum diameter of 1-inch.
. U,T, L,or C shape steel posts with a minimum weight of 1.35 lbs./ft.
. Other steel posts having equivalent strength and bending resistance to the post
sizes listed above.
11. Locate silt fences on contour as much as possible,except at the ends of the fence,
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 373
where the fence shall be turned uphill such that the silt fence captures the runoff water
and prevents water from flowing around the end of the fence.
12. If the fence must cross contours,with the exception of the ends of the fence,place
check dams perpendicular to the back of the fence to minimize concentrated flow and
erosion.The slope of the fence line where contours must be crossed shall not be
steeper than 3H:1 V.
. Check dams shall be approximately 1-foot deep at the back of the fence. Check
dams shall be continued perpendicular to the fence at the same elevation until
the top of the check dam intercepts the ground surface behind the fence.
. Check dams shall consist of crushed surfacing base course,gravel backfill for
walls,or shoulder ballast.Check dams shall be located every 10 feet along the
fence where the fence must cross contours.
Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details.The
following are specifications for silt fence installation using the slicing method:
1. The base of both end posts must be at least 2-to 4-inches above the top of the geo-
textile fabric on the middle posts for ditch checks to drain properly.Use a hand level or
string level, if necessary,to mark base points before installation.
2. Install posts 3-to 4-feet apart in critical retention areas and 6-to 7-feet apart in standard
applications.
3. Install posts 24-inches deep on the downstream side of the silt fence,and as close as
possible to the geotextile fabric,enabling posts to support the geotextile fabric from
upstream water pressure.
4. Install posts with the nipples facing away from the geotextile fabric.
5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8-
inches of the fabric.Attach each tie diagonally 45 degrees through the fabric,with each
puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post
nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure
with 3 ties.
7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level.
8. Compact the soil immediately next to the geotextile fabricwith the frontwheel of the
tractor, skid steer,or roller exerting at least 60 pounds per square inch.Compact the
upstream side first and then each side twice for a total offourtrips.Check and correct
the silt fence installation for any deviation before compaction.Use a flat-bladed shovel
to tuck the fabric deeper into the ground if necessary.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter3-Page 374
Figure 11-3.23: Silt Fence Installation by Slicing Method
Ponding height max.24"
POST SPACING: 1
7'max.on open runs '.
Attach fabric to 4'max.on pooling areas Top of Fabric
upstream side of post Belt
FLOW y POST DEPTH: top 8"
Drive over each side of As much below ground
sill fence 2 to 4 times as fabric above ground
with device exerting 60
p.s.i.or greater
Diagonal attachment
100%compaction 100%compaction doubles strength
1=III-IIL—I I L-1 I—IIHI �I-111-111
=THIL=>I I=1 i i i HIH-LG1�=uH1
�L=11H11=I I-W��H=W=Ill=
1—III=ll o IIH k� M—III-
I-111—III—III— nI—III—�-I—
I�Tl=1I1=1I c H —III— Attachment Details
111=III o 1 HJ=11HIH11-111
III—III I— I.a 1 H 1-111=III=III= Gather fabric at posts,if needed.
HIM I h =M—h— H =1I Utilize three ties per post,all within top 8"
=L— — �G
=)II-IIHIIHII °'1=IIHIHII=IIHI of fabric.
T° I1=1I —II1= Position each tie diagonally,puncturing
f=)I)=111=1J1 1=1f.HLIHIJj�,P holes vertical) a minimum of 1"apart.
—ITI= HI I— —I H -11-1 Y P
LGjlrl-j II Hang each lie on a post nipple and tighten
No more than 24"of a 36' securely.Use cable ties(50 Ibs)or soft
fabric is allowed above ground wire. 1
f Operation Ro1I of It fence
Post
installed
Fabric after
above compaction
Oground Silt Fence
_L
I—I�II—T rf —1
=1 i 011 —1300 j
_—
�II
Horizontal chisel point Slicing blade — -
(76 mm width) (18 mm width)
Completed Installation
Vibratory plow is not acceptable because of horizontal compaction NOT TO SCALE
WIN
Silt Fence Installation by Slicing Method
Revised.June 2016
DEPARTMENT OF
ECOLOGY Please see http://www.ecy.wa.gov/copyrghthtml for copyright notice including permissions,
State of Washingtoml limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume ll-Chapter3-Page 375
Maintenance Standards
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap-
ping BMP.
• Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to
flow and then causing channelization of flows parallel to the fence. If this occurs, replace the
fence and remove the trapped sediment.
• Remove sediment deposits when the deposit reaches approximately one-third the height of
the silt fence, or install a second silt fence.
• Replace geotextile fabric that has deteriorated due to ultraviolet breakdown.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 376
BMP C240: Sediment Trap
Purpose
A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store sed-
iment from sites during construction. Sediment traps, along with other perimeter controls,shall be
installed before any land disturbance takes place in the drainage area.
Conditions of Use
• Sediment traps are intended for use on sites where the tributary drainage area is less than 3
acres,with no unusual drainage features,and a projected build-out time of six months or less.
The sediment trap is a temporary measure(with a design life of approximately 6 months)and
shall be maintained until the tributary area is permanently protected against erosion by veget-
ation and/or structures.
. Sediment traps are only effective in removing sediment down to about the medium silt size
fraction.Runoff with sediment of finer grades(fine silt and clay)will pass through untreated,
emphasizing the need to control erosion to the maximum extent first.
• Projects that are constructing permanent Flow Control BMPs,or Runoff Treatment BMPs
that use ponding for treatment, may use the rough-graded or final-graded permanent BMP
footprint for the temporary sediment trap.When permanent BMP footprints are used as tem-
porary sediment traps,the surface area requirement of the sediment trap must be met. If the
surface area requirement of the sediment trap is larger than the surface area of the per-
manent BMP,then the sediment trap shall be enlarged beyond the permanent BMP footprint
to comply with the surface area requirement.
2019 Stormwater Management Manual for Western Washington
Volume//-Chapter -Page 383
. A floating pond skimmer maybe used for the sediment trap outlet if approved by the Local Per-
mitting Authority.
. Sediment traps may not be feasible on utility projects due to the limited work space or the
short-term nature of the work. Portable tanks may be used in place of sediment traps for utility
projects.
Design and Installation Specifcations
. See Figure II-3.26:Cross Section of Sediment Trap and Figure II-3.27:Sediment Trap Outlet
for details.
. To determine the sediment trap geometry,first calculate the design surface area(SA)of the
trap, measured at the invert of the weir. Use the following equation:
SA= FS(Q2Ns)
where
Q2=
Option 1 -Single Event Hydrograph Method:
QZ= Peakvolumetric flow rate calculated using a 10-minute time step from a Type 1A,
2-year,24-hour frequency storm for the developed condition.The 10-year peakvolu-
metric flow rate shall be used if the project size,expected timing and duration of con-
struction,or downstream conditions warrant a higher level of protection.
Option 2-For construction sites that are less than 1 acre,the Rational Method may be
used to determine QZ.
Vs=The settling velocity of the soil particle of interest.The 0.02 mm(medium silt) particle with
an assumed density of 2.65 g/cm3 has been selected as the particle of interest and has a set-
tling velocity(Vs)of 0.00096 f/sec.
FS=A safety factor of 2 to account for non-ideal settling.
Therefore,the equation for computing sedimenttrap surface area becomes:
SA=2 x Q2/0.00096
or
2080 square feet per cfs of inflow
. Sediment trap depth shall be 3.5 feet minimum from the bottom of the trap to the top of the
overflow weir.
. To aid in determining sediment depth,all sediment traps shall have a staff gauge with a prom-
inent mark 1-foot above the bottom of the trap.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter3-Page 364
. Design the discharge from the sediment trap by using the guidance for discharge from tem-
porary sediment ponds in BMP C241: Sediment Pond(Temporary).
Maintenance Standards
. Sediment shall be removed from the trap when it reaches 1-foot in depth.
. Any damage to the trap embankments or slopes shall be repaired.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 385
Figure 11-3.26: Cross Section of Sediment Trap
Surface area determined q'Min.
at top of weir
1'Min. Overflow
1'Min
3.5'•5'
�} 1.5'Min.
Flat Bottom
Washed gravel
Discharge to
Note:Trap may be formed by berm or by Geotextile stabilized
partial or complete excavation. conveyance,
2"-4"Rock outlet,or level
Rip Rap spreader
NOTTOSCALE
Cross Section of Sediment Trap
Revised June 2016
DEPARTMENT OF
ECOLOGY Please see http:/MMhv.aoyWa.govIc pyrghthtml for copyright notice including permissions,
State of Washington I limitation of liability,and disclaimer.
2019 StormwaterManagement Manual for Western Washington
Volume It- Chapter 3-Page 386
Figure 11-3.27: Sediment Trap Outlet
6'Min.
1'Min.depth overflow spillway
ti ,:) y. ski,ea.
'S r�N.�.+a+� . may{ _ Min.1'depih 2"-4"rock
_ th
Native soil or _ _ — — Min.1'de P Y4" -1.5'
compacted backrill washed gravel
Geotextile
NOT TO SCALE
rr�
Sediment Trap Outlet
Revised June 2016
DEPARTMENT OF
ECOLOGY please see hitp:/Amw..e y.wa.govlwpyrighthtrM for copyright notice including permissions,
State of Washington limitation of liability,and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 11-Chapter 3-Page 387
Ben Root Skate Park
MacKay+Sposito construction SwPPP
March 7, 2023
Attachment D. Construction Stormwater Site Inspection Form
Construction Stormwater Site Inspection Form
Project Name Permit# Inspection Date Time
Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector If less than one acre
Print Name:
Approximate rainfall amount since the last inspection(in inches):
Approximate rainfall amount in the last 24 hours (in inches):
Current Weather Clear ❑ Cloudy ❑ Mist ❑ Rain ❑ Wind ❑ Fog ❑
A.Type of inspection: Weekly Post Storm Event Other
B. Phase of Active Construction (check all that apply):
Pre-con/installation of erosion/sedimentcontrols Clearing/Demo/Grading Infrastructure/storm/roads
Concrete pours Vertical Construction/buildings Utilities
Offsite improvements Site temporary stabilized Final stabilization
C.Questions:
1. Were all areas of construction and discharge points inspected? Yes No
2. Did you observe the presence of suspended sediment,turbidity,discoloration,or oil sheen Yes No
3. Was a water quality sample taken during inspection? (refer to permit conditions S4&S5) Yes No
4. Was there a turbid discharge 250 NTU or greater,or Transparency 6 cm or less?* Yes _ No
5. If yes to#4 was it reported to Ecology? Yes No
6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No
If answering yes to a discharge, describe the event. Include when,where,and why it happened;what action was taken,
and when.
*If answering yes to#4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/transparency is 33
cm or greater.
Sampling Results: Date:
Parameter Method(circle one) Result Other/Note
NTU I cm pH
Turbidity tube, meter, laboratory
pH Paper, kit, meter
Page 1
Construction Stormwater Site Inspection Form
D. Check the observed status of all items. Provide"Action Required"details and dates.
Element # Inspection BMPs BMP needs BMP Action
Inspected maintenance failed required
yes no n/a (describe in
section F)
1 Before beginning land disturbing
Clearing activities are all clearing limits,
Limits natural resource areas(streams,
wetlands, buffers,trees) protected
with barriers or similar BMPs?(high
visibility recommended)
2 Construction access is stabilized
Construction with quarry spalls or equivalent
Access BMP to prevent sediment from
being tracked onto roads?
Sediment tracked onto the road
way was cleaned thoroughly at the
end of the day or more frequent as
necessary.
3 Are flow control measures installed
Control Flow to control stormwater volumes and
Rates velocity during construction and do
they protect downstream
properties and waterways from
erosion?
If permanent infiltration ponds are
used for flow control during
construction,are they protected
from siltation?
4 All perimeter sediment controls
Sediment (e.g. silt fence,wattles,compost
Controls socks, berms,etc.)installed,and
maintained in accordance with the
Stormwater Pollution Prevention
Plan (SWPPP).
Sediment control BMPs (sediment
ponds,traps,filters etc.) have been
constructed and functional as the
first step of grading.
Stormwater runoff from disturbed
areas is directed to sediment
removal BMP.
5 Have exposed un-worked soils
Stabilize been stabilized with effective BMP
Soils to prevent erosion and sediment
deposition?
Page 2
Construction Stormwater Site Inspection Form
Element # Inspection BMPs BMP needs BMP Action
Inspected maintenance failed required
yes no n/a (describe in
section F)
5 Are stockpiles stabilized from erosion,
Stabilize Soils protected with sediment trapping
Cont. measures and located away from drain
inlet,waterways,and drainage
channels?
Have soils been stabilized at the end of
the shift, before a holiday or weekend
if needed based on the weather -
forecast?
Has stormwater and ground water
6 been diverted away from slopes and
Protect disturbed areas with interceptor dikes,
Slopes pipes and or swales?
Is off-site storm water managed
separately from stormwater generated
on the site?
Is excavated material placed on uphill
side of trenches consistent with safety
and space considerations?
Have check dams been placed at
regular intervals within constructed
channels that are cut down a slope?
7 Storm drain inlets made operable
Drain Inlets during construction are protected.
Are existing storm drains within the
influence of the project protected?
8 Have all on-site conveyance channels
Stabilize been designed,constructed and
Channel and stabilized to prevent erosion from
Outlets expected peak flows?
Is stabilization,including armoring
material,adequate to prevent erosion
of outlets,adjacent stream banks,
slopes and downstream conveyance
systems?
9 Are waste materials and demolition
Control debris handled and disposed of to
Pollutants prevent contamination of stormwater?
Has cover been provided for all
chemicals,liquid products,petroleum
products,and other material?
Has secondary containment been
provided capable of containing 110%
of the volume?
Were contaminated surfaces cleaned
immediately after a spill incident?
Were BMPs used to prevent
contamination of stormwater by a pH
modifying sources?
Page 3
Construction Stormwater Site Inspection Form
Element # Inspection BMPs BMP needs BMP Action
Inspected maintenance failed required
yes no n/a (describe in
section F)
9 Wheel wash wastewater is handled
Cont. and disposed of properly.
10 Concrete washout in designated areas.
Control No washout or excess concrete on the
Dewatering ground.
Dewatering has been done to an
approved source and in compliance
with the SWPPP.
Were there any clean non turbid
dewatering discharges?
11 Are all temporary and permanent
Maintain erosion and sediment control BMPs
BMP maintained to perform as intended?
12 Has the project been phased to the
Manage the maximum degree practicable?
Project Has regular inspection,monitoring and
maintenance been performed as
required by the permit?
Has the SWPPP been updated,
implemented and records maintained?
13 Is all Bioretention and Rain Garden
Protect LID Facilities protected from
sedimentation with appropriate BMPs?
Is the Bioretention and Rain Garden
protected against over compaction of
construction equipment and foot
traffic to retain its infiltration
capabilities?
Permeable pavements are clean and
free of sediment and sediment laden-
water runoff. Muddy construction
equipment has not been on the base
material or pavement.
Have soiled permeable pavements
been cleaned of sediments and pass
infiltration test as required by
stormwater manual methodology?
Heavy equipment has been kept off
existing soils under LID facilities to
retain infiltration rate.
E. Check all areas that have been inspected. ✓
All in place BMPs ❑ All disturbed soils ❑ All concrete wash out area All material storage areas ❑
All discharge locations ❑ All equipment storage areas ❑ All construction entrances/exits ❑
Page 4
Construction Stormwater Site Inspection Form
F. Elements checked"Action Required" (section D) describe corrective action to be taken. List the element number;
be specific on location and work needed. Document,initial,and date when the corrective action has been completed
and inspected.
Element Description and Location Action Required Completion Initials
# Date
Attach additional page if needed
Sign the following certification:
"I certify that this report is true, accurate,and complete,to the best of my knowledge and belief"
Inspected by: (print) (Signature) Date:
Title/Qualification of Inspector:
Page 5
TAB 3 (MINIMUM REQUIREMENT#3)
• 1-3.4.3 Minimum Requirement#3—Source Control of Pollution
All known, available and reasonable source control BMP's must be applied to all projects. Source
control BMP's must be selected, designed, maintained according to the reference Ecology Manual.
The intent of source control BMP's is to prevent stormwater from coming in contact with pollutants.
They are a cost-effective means of reducing pollutants in stormwater and should be considered in all
projects.
Supplemental Guidelines
Source Control BMPs include Operational BMPs and Structural Source Control BMPs. See Volume IV
for design details of these BMPs. For construction sites, see II-3.2 Construction Source Control BMPs.
Structural Source Control BMPs should be identified in the stormwater site plan and should be shown
on all applicable plans submitted for local government review and approval.
An adopted and implemented Basin Plan (see Appendix I-B: Basin Plans) or Total Maximum Daily Load
(see 1-2.13 Total Maximum Daily Loads (TMDLs)) may be used to develop more stringent source
control requirements that are tailored to a specific basin.
Identifying Source Control Strategies in a Basin Plan
Basin Plans can identify potential sources of pollution within the basin and develop strategies to
eliminate or control these sources to protect beneficial uses.
A Basin Plan can include the following Source Control strategies:
1. Detection and correction of illicit discharges to storm sewer systems, including the use of dry
weather sampling and dye-tracing techniques;
2. Identification of existing businesses, industries, utilities, and other activities that may store
materials susceptible to spillage or leakage of pollutants into the storm sewer system or to the
ground via wells, drains, or sumps;
3. Elimination or control of pollutant sources identified in (2);
4. Identification and control of future businesses, industries, utilities, and other activities which may
store materials susceptible to spillage or leakage of pollutants into the storm sewer system; and
5. Training and public education
A Basin Plan that incorporates the standard requirements from this section as well as more stringent
requirements does not require Ecology approval.
What Source Control BMP's are applicable to your project?
S417 -Stormwater maintenance. S421 - Parking lots, S411 -Vegetation management, S435-Pest
management. S450-Irrigation. S436-Color events, S442-Drain labels, S443- Fertilizer
Version Date: August 30, 2022
TAB 4 (MINIMUM REQUIREMENT#4)
1-3.4.4 Minimum Requirement#4— Preservation of Natural Drainage Systems and Outfalls
Natural drainage patterns shall be maintained and discharges from the project shall occur at the natural
location, to maximum extent practicable. The manner by which runoff is discharged from the project site
must not cause a significant adverse impact to downstream receiving waters and down gradient
properties. All outfalls require energy dissipation.
The objective is to preserve and utilize drainage systems to the fullest extent because of the multiple
stormwater benefits these systems provide; and to prevent erosion at the downstream of the discharge
location.
Refer to the referenced section of the manual for supplemental guidelines and additional information
under this section.
Will this project disturb the Natural Drainage System or Outfall of the project Site? Yes\No. If
yes, refer to section 1-3.4.4 for Supplemental Guidelines for additional information.
There will be no disruption to any natural drainage or outfall.
Version Date: August 30, 2022
�`rap �aborne, Inv-
CONSULTING ENGINEERS
TECHNICAL MEMORANDUM
TO: STEVE LANGE, CITY OF ANACORTES
FROM: STACEY CLEAR, P.E.
DATE: MARCH 3, 2023
SUBJECT: BASIN F3 AND F4 STORMWATER
MODELING ANALYSIS
CITY OF ANACORTES SKAGIT COUNTY,
WASHINGTON
G&O 42346 1.00
INTRODUCTION
Historically, as noted in the City of Anacortes' (City) current Stormwater Management
Plan,the downstream system of Basin F4 was undersized. Numerous developments
upstream would be allowed a flow control exemption if this surcharging condition was
remedied. In light of this,the City requested Gray& Osborne perform a new analysis of
the Basins F3 and F4 stormwater trunkline,to determine if any areas are anticipated to
surcharge based on current rainfall records. If surcharging is present within the updated
Model, any Developer who is developing within these basins may be required to provide
flow control,whereas if no surcharging is present within the Model,the Developer may L
be allowed a direct discharge to the water without having to do flow control
requirements. The following summarizes the specific Tasks that have been requested.
• Determine if any areas surcharge within the Basin F3 and F4 Conveyance
System.
• Propose solutions if any areas surcharge..
The following Memorandum provides analysis of these issues related to the Basin F3 and
F4 Conveyance System.
MODELING SETUP
The initial step to the analysis involved recreating the Stormwater Model as the previous
Model was done using MIKE URBAN software which was no longer available to
Gray & Osborne. The City has provided their storm system data in GIS, which includes
pipe sizes, lengths, and invert elevations. Rim elevations for each catch basin were
estimated using the Puget Sound 2017 LiDAR data available on the Washington DNR
website. This data, along with current GIS-based data(including catch basin/manhole
measure downs)provided by the City, was used to build the Hydraulic Model in
XPStorm, a SWMM-based modeling program. An overview of the subbasins within
Basin F3 and F4 are illustrated in Figure 1. The main trunkline for Basin F3 ranges from
22na Street to 30th Street, between D Avenue and R Avenue, where it eventually
discharges towards the west into Fidalgo Bay (see Figure 2). The main trunkline for
Basin F4 ranges from 24 h Street to 41 s Street, between D Avenue to T Avenue, where it
Page 1 of 7
3710 168fn Street NE,Building B,Suite 210 Arlington,Washington 98223 (360) 454-5490 Fox(360)454-5491
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3, 2023
then discharges westerly into Fidalgo Bay. In order to be conservative, no upstream
detention facilities were included in the modeling, assuming that these facilities may not
be maintained in the future and would be in constant overflow mode. This includes the
existing detention pond located near 25' Street(east of H Avenue) in Basin F3, and at
27`h Place near Creekside Place, also within Basin F3. In these instances, a pipe was
modeled in place of the detention pond.
There are 27 subbasins for Basin F3 and 18 subbasins for Basin F4. These were
developed in GIS by determining grade breaks using topographic data, as well as using
the City's GIS-based collection system data to determine the extents and the direction of
flow within each subbasin. The size for each of the subbasins is documented in Table 1.
The entire F3 Basin covers approximately 364 acres, whereas the F4 Basin covers
approximately 1,359 acres. It should be noted that the F4 Basin area includes the Ace of
Hearts Creek Basin as well(see Figure 1). This basin was modeled as flow entered into
Subbasin F4-5.
TABLE 1
Subbasin Areas
Subbasin ID Area acres Subbasin ID Area acres
F3-1 79 F4-1 87
F3-2 9 F4-2 13
F3-3 10 F4-3 6
F34 39 F4-4 9
F3-5 2 F4-5 758
F3-6 2 F4-6 43
F3-7 4 F4-7 33
F3-8 7 F4-8 35
F3-9 30 174-9 23
F3-10 9 174-10 11
F3-11 13 174-11 16
F3-12 5 F4-12 224
F3-13 35 F4-13 21
F3-14 5 F4-14 18
173-15 11 F4-15 20
F3-16 12 F4-16 19
173-17 7 F4-17 17
F3-18 8 F4-18 6
173-19 15 Total F4 Area acres 1,359
F3-20 16
F3-21 7
F3-22 8
F3-23 5
F3-24 5
F3-25 9
t:
Page 2 of 7
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3, 2023
TABLE 1 —(continued)
Subbasin Areas
Subbasin ID Area acres Subbasin ID Area acres
F3-26 8
F3-27 4
Total F3 Area acres 364
Land cover within each basin was determined in GIS using zoning designations (see
Table 2 and Figure 1). The maximum amount of impervious cover allowed by the City's
Zoning Code was assumed in order to simulate the buildout level of development that
may occur within the basin. According to the City's Code,the Public Zoning
Classification has the potential for a maximum impervious coverage of 100 percent. For
this Modeling Analysis,due to presence of forestland, it was assumed that the Public
Zoning Classification would be considered as fully landscaped, since there is no
expectation of this area being developed.
TABLE 2
Impervious Surface Coverage
Maximum Minimum Mandated
Zoning Code Zoning Designation Impervious Cover Landscaping
P Public 00/0 100%
I Industrial 90% 10%
C Commercial 90% 10%
CM Commercial Marine 85% 15%
R4A High-Density 50% 20%
Residential
R3 High-Density 50% 20%
Residential
R1 Low-Density 35% 20%
Residential
(1) Typically,the Public Zoning Classification allows up to 100 percent imperviousness,but due to
the presence of forestland,it was assumed that Public Classification for this analysis would
result in 0 percent imperviousness.
It is assumed that any additional area aside from the maximum impervious cover and
minimum required landscaping area will be composed of open space or less-manicured
pervious area.
Page 3 of 7
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3,2023
The time of concentration was determined for each subbasin using the Kinematic Wave
Method, which requires the following equation and input parameters.
Lo.unu.n
t,. =0.93� , A V.3
Where:
• L—Length of Overland Flow(feet)
• S=Average Catchment Slope(feet/feet)
• i=Rainfall Intensity (inches/hour)
• n—Surface Roughness
o Concrete or Asphalt—0.010 to 0.013
o Bare Sand—0.010 to 0.016
o Graveled Surface—0.012 to 0.030
o Bare Clay-Loam Soil (eroded)—0.012 to 0.033
o Sparse Vegetation—0.053 to 0.130
o Short-Grass Prairie—0.100 to 0.200
o Lawns—0.170 to 0.480
The flow path length and slope were determined using GIS topography data and subbasin
polygons. Per NOAA Atlas information, the 25-year rainfall event for Anacortes is
typically measured at 2.5 inches over 24 hours and is often distributed in a Hydraulic
Model, using the high intensity SCS Type IA Hydrograph. As a comparison to this, a
review of rainfall within the City over the past two years was conducted. Rainfall totals
measured every 30 minutes were obtained from the City's rain gauge. From this data, it
appears that the peak rainfall occurred on December 21, 2020, which amounted to
1.87 inches over a 24 hour period. Per City staff s direction, the City's rainfall data was
used for this Model. Surface roughness for each type of assumed land cover was selected
based on the typical ranges previously noted.
The Model first calculated runoff from each subbasin and then loaded this flow to the
specified location along the modeled main. At the request of the City, a safety factor of
1.5 was applied to the calculated flow to account for anticipated groundwater seepage.
The modeled improvements assume that the model storm event must be contained within
the pipe, with no surcharging above the pipe crown at the time of peak flow.
Page 4 of 7
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3, 2023
The full basin peak flow to the F3 Outfall is calculated at 37 cfs, whereas the F4 Basin
Outfall showed 98 cfs. Both of these peak outfall calculations already include the
50 percent factor of safety.
MODELING PARAMETERS SUMMARY
A number of parameters are input to the Model to calculate runoff and determine system
capacity. A summary is included in Table 3.
TABLE 3
Modeling Input Summary
Parameter Value Rationale
Rainfall Recurrence December 21, 2020 storm Standard for Conveyance
Interval from City Rain Gauge; Analysis.
1.87 inches per day.
Runoff Safety Factor 150% Requested by City.
Manning's Roughness Conservative value to reflect
Coefficient 0.013 roughness of concrete pipes.
Landscaping Curve Moderately maintained lawn or
Number 87 landscaped area over Type C
soils.
Other Pervious Area Moderately well-covered,
Curve Number 75 non-maintained pervious area
over Type C soils.
Impervious Area 98 Standard for impervious area.
Curve Number
Time of Reasonable method for
Concentration Method Kinematic Wave moderately sized basins(flow
paths over 300 feet, but basin area
smaller than 1 square mile).
Kinematic Wave Impervious Area: 0.012 Typical parameters provided
Roughness Landscaping: 0.25 above.
Other Pervious Area: 0.4
MODEL RESULTS
The existing pipe system was modeled to determine which pipes, if any, are insufficient
for the modeled flow anticipated under a built-out condition. The results of the Model
may be found visually, in Figures 2 and 3, with the tabular data located at the end of this
Memorandum. The Model results revealed that 17 pipes in the F3 Basin and 4 pipes in
the F4 Conveyance System are anticipated to have insufficient capacity for the modeled
storm (plus an additional 50 percent contingency factor). The necessary pipe
replacements needed to resolve these surcharged areas are listed in Table 4 and are shown
in Figures 2 and 3 for Basin F3 and Basin F4, respectively.
Page 5 of 7
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3, 2023
TABLE 4
Recommended Pipe Improvements
Existing Necessary
Pipe Size Pipe Size 0) Length Surcharging
Basin Location inches inches feet Amount feet
22nd Street
F3 (Between North Avenue 21 30 436 6.5
and O Avenue
22nd Street
F3 (Between SR 20 and O 27 30 147 0.1
Avenue
SR 20
F3 (Between 23'd Street and 8 18 248 2.6
24' Street
F3 24"Place 8 12 126 0.8
West of J Avenue
241' Street
F3 (Between N Avenue and 8 12 344 3.5
O Avenue)
L Avenue
F3 (Between 250'Street and 10 18 217 4.4
26d'Street)
J Avenue
F3 (Between 26' Street and 15 24 268 4.2
28'Street
F3 27"Place 12 18 139 0.7
(North of 28'Street)
I Avenue
F3 (Between 29' Street and 8 12 854 0.4—3.5
31I'Street)
F3 29" Street 8 12 728 2.1 —7.0
West of SR 20
M Avenue
F4 (Between 32"d and 33'd 24 30 236 7.2
Street
R Avenue
F4 (Between 32"dStreet 12/27 30 591 7.4
and 34'Street
Page 6 of 7
Technical Memorandum—Basin F3 and F4 Stormwater Modeling Analysis
March 3, 2023
TABLE 4—(continued)
Recommended Pipe Improvements
Existing Necessary
Pipe Size Pipe Size(') Length Surcharging
Basin Location inches inches feet Amount feet
F4 M Avenue(KingStreet 15 18 185 1.6
M Avenue 8
F4 South of 39i°Street (Verify) 15 26 0.9
(1) Assumes no allowable surcharging above the pipe. Pipes were sized to contain 150 percent of the
anticipated basin flow to account for groundwater concerns.
Replacing the pipes allow for the model storm (plus 50 percent contingency factor)to be
fully contained within the pipes with no surcharging. It appears these pipes will have
sufficient cover but the pipe diameters, orientation, and slopes should all be verified
during the design process.
SUMMARY
Any construction upstream of the pipes listed in Table 4 would necessitate either flow
control onsite or the replacement of the pipes with the recommended size however, it
would be prudent to survey these pipes prior to design to verify the accuracy of the
system modeled.
In addition, from the Model results, it appears that the existing detention ponds in
Basin F3 should not be taken offline due to downstream constraints however, the existing
ponds located along H Avenue in Basin F4 could potentially be taken offline due to the
presence of no modeled downstream constraints.
Page 7 of 7