24-100902-SWPPP-3.15.24Construction Stormwater General Permit (CSWGP)
Stormwater Pollution Prevention Plan
(SWPPP)
for
Penwell Property
Prepared for:
Department of Ecology
Northwest Regional Office
Permittee / Owner Developer Operator / Contractor
Chris Penwell Chris Penwell To be determined
South end of 2nd Ave SW, Federal Way
Certified Erosion and Sediment Control Lead (CESCL)
Name Organization Contact Phone Number
TBD TBD TBD
SWPPP Prepared By
Name Organization Contact Phone Number
Vicente Varas Barghausen Consulting
Engineers, Inc.
(425) 251-6222
SWPPP Preparation Date
August 03, 2023
Project Construction Dates
Activity / Phase Start Date End Date
Clear/Grade/Utilities/Building April / 01 / 2024 December / 01 / 2024
Table of Contents
1 Project Information ................................................................................................................. 4
1.1 Existing Conditions ......................................................................................................... 5
1.2 Proposed Construction Activities .................................................................................... 6
2 Construction Stormwater Best Management Practices (BMPs) ............................................ 7
2.1 The 13 Elements ............................................................................................................ 8
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits .......................................... 8
2.1.2 Element 2: Establish Construction Access .............................................................. 9
2.1.3 Element 3: Control Flow Rates .............................................................................. 10
2.1.4 Element 4: Install Sediment Controls .................................................................... 11
2.1.5 Element 5: Stabilize Soils ...................................................................................... 13
2.1.6 Element 6: Protect Slopes ..................................................................................... 15
2.1.7 Element 7: Protect Drain Inlets .............................................................................. 16
2.1.8 Element 8: Stabilize Channels and Outlets ........................................................... 17
2.1.9 Element 9: Control Pollutants ................................................................................ 18
2.1.10 Element 10: Control Dewatering ........................................................................... 25
2.1.11 Element 11: Maintain BMPs .................................................................................. 26
2.1.12 Element 12: Manage the Project ........................................................................... 27
2.1.13 Element 13: Protect Low Impact Development (LID) BMPs .................................. 28
3 Pollution Prevention Team ................................................................................................... 29
4 Monitoring and Sampling Requirements .............................................................................. 30
4.1 Site Inspection .............................................................................................................. 30
4.2 Stormwater Quality Sampling ....................................................................................... 30
4.2.1 Turbidity Sampling ................................................................................................. 30
4.2.2 pH Sampling .......................................................................................................... 32
5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies ......................... 33
5.1 303(d) Listed Waterbodies ........................................................................................... 33
5.2 TMDL Waterbodies ....................................................................................................... 33
6 Reporting and Record Keeping ........................................................................................... 34
6.1 Record Keeping ............................................................................................................ 34
6.1.1 Site Log Book ........................................................................................................ 34
6.1.2 Records Retention ................................................................................................. 34
6.1.3 Updating the SWPPP ............................................................................................ 34
6.2 Reporting ...................................................................................................................... 35
6.2.1 Discharge Monitoring Reports ............................................................................... 35
6.2.2 Notification of Noncompliance ............................................................................... 35
List of Tables
Table 1 – Summary of Site Pollutant Constituents ....................................................................... 5
Table 2 – Pollutants .................................................................................................................... 18
Table 3 – pH-Modifying Sources ................................................................................................. 23
Table 5 – Management ............................................................................................................... 27
Table 6 – BMP Implementation Schedule ................................................................................... 27
Table 7 – Team Information ........................................................................................................ 29
Table 8 – Turbidity Sampling Method ......................................................................................... 30
Table 9 – pH Sampling Method .................................................................................................. 32
List of Appendices
A. Site Map
B. BMP Detail
C. Correspondence
D. Site Inspection Form
E. Construction Stormwater General Permit (CSWGP)
F. 303(d) List Waterbodies / TMDL Waterbodies Information
G. Contaminated Site Information
H. Engineering Calculations
List of Acronyms and Abbreviations
Acronym / Abbreviation Explanation
303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies
BFO Bellingham Field Office of the Department of Ecology
BMP(s) Best Management Practice(s)
CESCL Certified Erosion and Sediment Control Lead
CO2 Carbon Dioxide
CRO Central Regional Office of the Department of Ecology
CSWGP Construction Stormwater General Permit
CWA Clean Water Act
DMR Discharge Monitoring Report
DO Dissolved Oxygen
Ecology Washington State Department of Ecology
EPA United States Environmental Protection Agency
ERO Eastern Regional Office of the Department of Ecology
ERTS Environmental Report Tracking System
ESC Erosion and Sediment Control
GULD General Use Level Designation
NPDES National Pollutant Discharge Elimination System
NTU Nephelometric Turbidity Units
NWRO Northwest Regional Office of the Department of Ecology
pH Power of Hydrogen
RCW Revised Code of Washington
SPCC Spill Prevention, Control, and Countermeasure
su Standard Units
SWMMEW Stormwater Management Manual for Eastern Washington
SWMMWW Stormwater Management Manual for Western Washington
SWPPP Stormwater Pollution Prevention Plan
TESC Temporary Erosion and Sediment Control
SWRO Southwest Regional Office of the Department of Ecology
TMDL Total Maximum Daily Load
VFO Vancouver Field Office of the Department of Ecology
WAC Washington Administrative Code
WSDOT Washington Department of Transportation
WWHM Western Washington Hydrology Model
Project Information (1.0)
This Stormwater Pollution Prevention Plan (SWPPP) has been prepared per the requirements of
the Washington State NPDES Construction Stormwater General Permit Conditions of Approval
for the Penwell Property. The site is located within a portion of Section 6, Township 21 North,
Range 4 East, Willamette Meridian, in Federal Way, Washington.
The parcel for the property is 199600-3800 and contains an existing shared access road
connecting to 2nd Ave SW at the northeast corner of the site and extending to the neighboring
property on the southwest corner of the site. Onsite vegetation is mostly forested with an unnamed
stream flowing northwest bisecting the site on the east side. Elevations range from 136 to 202
feet across the site sloping down to the unnamed stream. The low point of the site is located at
the centerline of the stream as it leaves the site to the north. A portion of the slopes on-site exceed
40% in grade and may be considered a potential landslide hazard area.
This project will re-consturct and widen the existing shared access road and construct a single-
family residence on the southwest portion of the site. In addition, the project will install stormwater
pipes and catch basins, a stormwater detention system and water quality unit, sewer facilities and
water facilities to serve the property.
The purpose of this SWPPP is to describe the proposed construction activities and all temporary
and permanent erosion and sediment control (TESC) measures, pollution prevention measures,
inspection/monitoring activities, and recordkeeping that will be implemented during the proposed
construction project. The objectives of the SWPPP are to:
1. Implement Best Management Practices (BMPs) to prevent erosion and sediment, and
to identify, reduce, eliminate or prevent stormwater contamination and water pollution
from construction activity.
2. Prevent violations of surface water quality, ground water quality, or sediment
management standards.
3. During the construction phase prevent adverse water quality impacts including,
impacts of beneficial uses of the receiving water by controlling peak flow rates and
volumes of stormwater runoff at the Permittee's outfalls and downstream of the
outfalls.
This SWPPP was prepared using the Ecology SWPPP Template. The Template has been revised
to incorporate all items in the General NPDES Permit as well as provide more project specific
BMPs that will be utilized onsite. This SWPPP was prepared based on the requirements set forth
in the Construction Stormwater General Permit, Stormwater Management Manual for Western
Washington (SWMMWW 2012). The site project information for the site is summarized below.
Project/Site Name: Penwell Property
Street/Location: South End of 2nd Ave SW
City: Federal Way State: WA Zip code: 98023
Subdivision:
Receiving waterbody: Unnamed Stream and the Puget Sound
Existing Conditions (1.1)
Total acreage (including support activities such as off-site equipment staging yards, material
storage areas, borrow areas).
Total acreage: 0.94
Disturbed acreage: 0.31
Existing structures: None
Landscape topography: Most site topography slopes northeast towards the unnamed
stream on the east portion of the stie.
Drainage patterns: Stormwater runoff flows towards the unnamed stream and flows
northwest along the stream flowpath as it leaves the site near the
north boundary.
Existing Vegetation: Forested
Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes):
Steep Slopes, Wetland, Unnamed Stream
List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the
receiving waterbody:
Table 1 includes a list of suspected and/or known contaminants associated with the construction
activity.
Table 1 – Summary of Site Pollutant Constituents
Constituent
(Pollutant) Location Depth Concentration
None identified N/A N/A N/A
Proposed Construction Activities (1.2)
This project phase will consist of the construction of the re-construction of a shared access
road, single-family residence, stormwater utilities sewer facilities and water facilities. Stormwater
runoff in the fully developed stage will be routed to a water quality unit near the northeast corner
of the site before entering an underground stormwater detention system. After detention, runoff
will be discharged into the unnamed stream near the north boundary line using a rock lining
discharge pad.
Contaminated Site Information:
Ther are no known activities that will result in the contamination of soil and or groundwater
planned for the site during clearing, grading, an/or the construction of the development.
Construction Stormwater Best Management Practices (BMPs) (2.0)
The following sections describe BMPs that will be utilized during the construction of the project.
Alternate BMPs for the 13 BMP Elements may be implemented on a need by need basis, should
the 13 Elements below be deemed ineffective or inappropriate during the construction to satisfy
the requirements set forth in the General NPDES Permit. To avoid potential erosion and sediment
control issues that may cause violation(s) of the NPDES Construction Stormwater permit, the
Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or
more alternate BMPs after the first sign that existing BMPs are ineffective or failing.
A suggested BMP implementation schedule follows. Note that some of these BMPs will have
already been installed during the Early Clear and Grade permit. All BMPs should be verified for
compliance.
1. Mark clearing limits
2. Hold pre-construction conference
3. Install construction entrance
4. Install perimeter protection
5. Grade and stabilize construction roads and staging areas
6. Install surface water controls (interceptor swales and check dams) as clearing and grading
progresses
7. Install cover measures on all areas that will be unworked for more than 7 days during the
dry season or 2 days during the wet season
8. Install stabilization measures within 7 days of reaching final grade
9. Maintain erosion control measures and update BMPs as required by construction or
changes in site conditions
Upon project completion, stabilize all disturbed areas and remove BMPs when appropriate
The SWPPP is a living document reflecting current conditions and changes throughout the life
of the project. These changes may be informal (i.e. hand-written notes and deletions). Update
the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design.
Element 1: Preserve Vegetation / Mark Clearing Limits
To protect adjacent properties and to reduce the area of soil exposed to construction, the limits
of construction will be clearly marked before land-disturbing activities begin. Trees that are to be
preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the
field and on the plans. In general, natural vegetation and native top soil shall be retained in an
undisturbed state wherever practical. Native top soil which is cleared, and appropriate for reuse
on the site, shall be stockpiled separately and protected from contamination using silt fencing and
appropriate cover measures. The BMPs relevant to marking the clearing limits that will be applied
for this project include the following:
List and describe BMPs:
· High Visibility Fence (BMP C103) and Tree Protection Fence
Install colored orange fence to protect areas that are not to be disturbed, and mark trees
to be preserved.
· Silt Fence (BMP C233)
Silt fencing shall be used to reduce sediment flow offsite throughout the construction
process.
Installation Schedules: All BMPs to preserve vegetation and mark clearing limits are to be installed
prior to clearing and grading.
Inspection and Maintenance plan: All fencing is to be inspected at the end of each day's work and
following significant rain events. Repairs should be performed if found to be noncompliant with
BMP specifications.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 2: Establish Construction Access
Construction access or activities occurring on unpaved areas shall be minimized, yet where
necessary, access points shall be stabilized to minimize the tracking of sediment onto public
roads. Street sweeping and street cleaning shall be employed where necessary to prevent
sediment from entering state waters. All wash wastewater shall be controlled onsite. The specific
BMPs related to establishing construction access that will be used on this project are as follows:
List and describe BMPs:
· Stabilized Construction Entrance (BMP C105)
One quarry spall construction entrance will be placed at the end of 2nd Ave SW on the
northwest corner of the site. This stabilized construction entrance will be used to minimize
the amount of sediment transported off site onto the existing roadway by construction
traffic.
· Construction Road/Parking Area Stabilization (BMP C107)
Disturbed areas shall be stabilized immediately after desired grading to reduce erosion by
construction traffic or surface water runoff. A designated parking and maintenance area
shall be stabilized and maintained to help contain spills.
· Concrete Washout Area (BMP C154)
Conduct washout off-site, or perform on-site concrete washout in a designated area. This
is done to prevent pollutants from entering surface or ground water.
If sediment is tracked off site, clean the affected roadway thoroughly at the end of each day or
more frequently, as necessary. Remove sediment from roads by shoveling, sweeping, or pickup
and transport of the sediment to a controlled sediment disposal area.
Conduct street washing only after sediment removal in accordance with special condition
S9.D.2.d. Control street wash wastewater by pumping back on site or otherwise preventing it from
discharging off site into stormwater conveyance systems, creek, or rivers that connect to waters
of the State.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 3: Control Flow Rates
In order to protect the properties and waterways downstream of the project site, stormwater
discharges from the site will be controlled. The Specific BMPs for the flow control that shall be
used on this project include the following:
Will you construct stormwater retention and/or detention facilities?
Yes No
Will you use permanent infiltration ponds or other low impact development (example: rain
gardens, bio-retention, porous pavement) to control flow during construction?
Yes No
List and describe BMPs:
· Check Dams (BMP C207)
Check dams located within temporary roadside ditches will be be used to reduce the
velocity and energy of the concentrated low flows expected from the project before
discharging to the rock lining discharge pad.
The project site is located west of the Cascade Mountain Crest. As a result, the project must
comply with the Minimum Requirement 7 (Ecology 2012). Minimum Requirement 7 states that
projects must provide flow control to reduce the impacts of stormwater runoff from impervious
surfaces and land cover conversions.
Essentially, discharge rates of stormwater from the site will be controlled where increases in
impervious area or soil compaction during construction could lead to downstream erosion, or
where necessary to meet local agency stormwater discharge requirements (e.g. discharge to
combined sewer systems).
Installation Schedules: To be installed in the early stages of grading and utility construction.
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 4: Install Sediment Controls
All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal
BMP before leaving the construction site. The specific BMPs to be used for controlling sediment
on this project are as follows:
List and describe BMPs:
· Silt Fence (BMP C233)
During site development phase, silt fence will be used along the downhill perimeter of the
project to prevent sediment from leaving the site.
· Construction Stormwater Filtration (BMP C251) if needed
· Construction Stormwater Chemical Treatment (BMP C250) (Implemented only with prior
written approval from Ecology.)
Implement BMP C250/251 above end-of-pipe measures only if sediment sources and
erosion control and soil stabilization BMP efforts are not sufficient to reduce
sedimentation.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 5: Stabilize Soils
Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent
erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used
in this project are as follows:
West of the Cascade Mountains Crest
Season Dates Number of Days Soils Can
be Left Exposed
During the Dry Season May 1 – September 30 7 days
During the Wet Season October 1 – April 30 2 days
Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on
the weather forecast.
Anticipated project dates: Start date: April 2023 End date: December 2028
Will you construct during the wet season?
Yes No
List and describe BMPs:
· Temporary and Permanent Seeding (BMP C120)
Following final or fine grading activity in new pervious areas, permanent seeding shall be
placed on exposed soil to provide permanent erosion protection.
· Mulching (BMP C121)
During the site development phase, mulching will be used for areas that will be unworked
for more than 2 days. Temporary seeding will be applied to areas that will be unworked
for more than 7 days. During the building phase, the construction area will be significantly
stabilized through well established grass cover. Proposed driveways will receive base
course materials as described under Element #2 above. Areas cleared for building
foundations or utility and irrigation placement will be temporarily stabilized by one of the
following methods which are based on the period exposed soils are left unworked:
o If exposed soils are left unworked for more than 7 days during the dry season and
2 days during the wet season but less than 30 days, mulching shall be applied.
o If exposed soils are left unworked for more than 30 days, temporary or permanent
seeding shall be applied.
· Nets and Blankets (BMP C122)
Once final or fine grading activity has been completed, install Jute Matting on slopes prior
to planting.
· Sodding (BMP C124)
Following final or fine grading activity in the front yard, sod shall be placed on exposed
soil to provide permanent and immediate erosion protection.
· Plastic Covering (BMP C123)
· Topsoiling (BMP C125)
Utilize stockpile management during all phases of construction per BMP. Cover stockpiles
with plastic covering to prevent erosion during rain events.
· Wattles (BMP C235)
Install wattles downslope of newly landscaped areas to control sediment runoff until
stabilization.
Cement or Calcium Chloride may be used for soil stabilization and dewatering with prior approval.
See section 4.2.2 for pH Sampling Requirements.
The project site is located west of the Cascade Mountain Crest. As such, no soils shall remain
exposed and unworked for more than 7 days during the dry season (May 1 to September 30) and
2 days during the wet season (October 1 to April 30). Regardless of the time of year, all soils
shall be stabilized at the end of the shift before a holiday or weekend if needed based on weather
forecasts.
Cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily
covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion, protected with
sediment trapping measures, and where possible, be located away from storm drain inlets,
waterways, and drainage channels.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 6: Protect Slopes
All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes
erosion.
Will steep slopes be present at the site during construction?
Yes No
List and describe BMPs:
· Temporary and Permanent Seeding (BMP C120)
The site has steep slopes (more than 15%). Short sections of sloped grading will be
treated as described under Element 5 above.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 7: Protect Drain Inlets
The following BMPs will be used to protect catch basin inlets during construction:
List and describe BMPs:
· Storm Drain Inlet Protection (BMP C220).
Prior to construction, storm drain inlet protection will be utilized on all catch basins which
may receive stormwater from the construction area. Also install inlet protection once
permanent storm drain inlets on site are constructed.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 8: Stabilize Channels and Outlets
Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural
drainage point, efforts will be made to prevent downstream erosion. The specific BMPs for
channel and outlet stabilization that shall be used on this project include:
Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent
stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance
systems.
List and describe BMPs:
· Interceptor Dike and Swale (BMP C200)
During the site development phase, interceptor dikes and swales shall be constructed to
convey stormwater to the rock lining discharge pad.
· Check Dams (BMP C207)
Check dams shall be used to reduce the velocity and energy of concentrated flow in
ditches.
Installation Schedules: Installation schedule to be determined by the General Contractor
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 9: Control Pollutants
All pollutants, including waste materials and demolition debris, that occur onsite shall be handled
and disposed of in a manner that does not cause contamination of stormwater. Good
housekeeping and preventative measures will be taken to ensure that the site will be kept clean,
well organized, and free of debris. If required, BMPs to be implemented to control specific sources
of pollutants are discussed below.
The following pollutants are anticipated to be present on-site:
Table 2 – Pollutants
Pollutant (List pollutants and source, if applicable)
Grease, fuel, oils from construction equipment operation and maintenance
Trash from construction activity
Temporary Sanitary Facilities
Fertilizers (if used to establish lawn/landscaping areas)
Concrete products
List and describe BMPs:
Housekeeping BMPs
The following sections describe the controls, including storage practices to minimize exposure of
the materials to stormwater as well as spill prevention and response practices. All pollutants,
including waste materials and demolition debris, that occur onsite shall be handled and disposed
of in a manner that does not cause contamination of stormwater.
Vehicles, construction equipment, and/or petroleum product storage/dispensing:
· All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected
regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks
or spills. Secondary containment such as drip pans will be placed under any leaking
vehicles or equipment. All petroleum product storage containers will be placed in
secondary containment (see spill prevention and control below).
· On-site fueling tanks and petroleum product storage containers shall include secondary
containment.
· Spill prevention measures, such as drip pans, will be used when conducting maintenance
and repair of vehicles or equipment or when vehicle/equipment leaks are observed.
· In order to perform emergency repairs on site, temporary plastic will be placed beneath
and, if raining, over the vehicle.
· Contaminated surfaces shall be cleaned immediately following any discharge or spill
incident.
Chemical storage:
· Any chemicals stored in the construction areas will conform to the appropriate source
control BMPs listed in Volume IV of the Ecology stormwater manual. In Western WA, all
chemicals shall have cover, containment, and protection provided on site, per BMP C153
for Material Delivery, Storage and Containment in SWMMWW 2012.
· Application of agricultural chemicals, including fertilizers and pesticides, shall be
conducted in a manner and at application rates that will not result in loss of chemical to
stormwater runoff. Manufacturers’ recommendations for application procedures and rates
shall be followed.
Concrete and grout:
· Process water and slurry resulting from concrete work will be prevented from entering the
waters of the State by implementing Concrete Handling measures (BMP C151) and
Sawcutting and Surfacing Pollution Prevention (BMP C152).
Sanitary wastewater:
· Proper sanitary and septic waste management are waste management and material
pollution controls that prevent the discharge of pollutants to stormwater from sanitary and
septic waste by providing convenient, well-maintained facilities, and arranging for regular
service and disposal. Implement as follows:
o Facilities should be located away from drainage facilities, watercourses, and from
traffic circulation.
o Provide a sufficient quantity of facilities to accommodate the workforce.
o Temporary sanitary facilities must be equipped with containment to prevent
discharge of pollutants to the stormwater drainage system of the receiving water.
o When subjected to high winds or risk of high winds, temporary sanitary facilities
should be secured to prevent overturning.
o Sanitary facilities should be located in a convenient location.
o Sanitary or septic wastes should be treated or disposed of in accordance with state
and local requirements.
o Sanitary facilities should be maintained in good working order by a licensed
service.
Solid and Liquid Waste:
· Solid and liquid waste generated during construction such as construction materials,
contaminated materials, and waste materials from maintenance activities will be prevented
from entering the waters of the State. Solid and liquid waste shall be handled in
accordance with BMPs for Storage of Liquid, Food Waste, or Dangerous Waste
Containers and BMPs for Loading and Unloading Areas for Liquid or Solid Materials.
o Solid waste will be stored in secure, clearly marked containers.
o Promptly contain and clean up solid and liquid pollutant leaks and spills including
oils, solvents, fuels, and dust from manufacturing operations on any exposed soil,
vegetation, or paved area.
o Sweep paved material handling and storage areas regularly as needed, for the
collection and disposal of dust and debris that could contaminate stormwater. Do
not hose down pollutants from any area to the ground, storm drain, conveyance
ditch, or receiving water unless necessary for dust control purposes to meet air
quality regulations.
Installation Schedules: The described BMPs will be implemented while all pollution generating
materials are onsite.
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work.
Responsible Staff: Certified Erosion and Sediment Control Lead
Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site?
Yes No
If yes, describe spill prevention and control measures in place while conducting maintenance,
fueling, and repair of heavy equipment and vehicles.
If yes, also provide the total volume of fuel on-site and capacity of the secondary containment
for each fuel tank. Secondary containment structures shall be impervious.
List and describe BMPs:
Spill Prevention and Control BMPs
Prevent or reduce the discharge of pollutants to drainage systems or watercourses from leaks
and spills by reducing the chance for spills, stopping the source of spills, containing and cleaning
up spills, properly disposing of spill materials, and training employees. This best management
practice covers only spill prevention and control. However, Materials Delivery and Storage (BMP
C153), also contains useful information, particularly on spill prevention.
· To the extent that the work can be accomplished safely, spills of oil, petroleum products,
and substances listed under 40 CFR parts 110,117, and 302, and sanitary and septic
wastes should be contained and cleaned up immediately.
· Store hazardous materials and wastes in covered containers and protect from vandalism.
· Place a stockpile of spill cleanup materials where it will be readily accessible.
· Train employees in spill prevention and cleanup.
· Designate responsible individuals to oversee and enforce control measures.
· Spills should be covered and protected from stormwater runon during rainfall to the extent
that it doesn’t compromise cleanup activities.
· Do not bury or wash spills with water.
· Store and dispose of used clean up materials, contaminated materials, and recovered spill
material that is no longer suitable for the intended purpose in conformance with the
provisions in applicable BMPs.
· Do not allow water used for cleaning and decontamination to enter storm drains or
watercourses. Collect and dispose of contaminated water in accordance WSDOE
regulations.
· Contain water overflow or minor water spillage and do not allow it to discharge into
drainage facilities or watercourses.
· Place proper storage, cleanup, and spill reporting instructions for hazardous materials
stored or used on the project site in an open, conspicuous, and accessible location.
· Keep waste storage areas clean, well organized, and equipped with ample clean supplies
as appropriate for the materials being stored. Perimeter controls, containment structures,
covers, and liners should be repaired or replaced as needed to maintain proper function.
Cleanup:
· Clean up leaks and spills immediately.
· Use a rag for small spills on paved surfaces, a damp mop for general cleanup, and
absorbent material for larger spills. If the spilled material is hazardous, then the used
cleanup materials are also hazardous and must be sent to either a certified laundry (rags)
or disposed of as hazardous waste.
· Never hose down or bury dry material spills. Clean up as much of the material as possible
and dispose of properly.
· The spill kit should include, at a minimum:
o 1-Water Resistant Nylon Bag
o 3-Oil Absorbent Socks 3”x 4’
o 2-Oil Absorbent Socks 3”x 10’
o 12-Oil Absorbent Pads 17”x19”
o 1-Pair Splash Resistant Goggles
o 3-Pair Nitrile Gloves
o 10-Disposable Bags with Ties
o Instructions
· Spill kits will be located in areas with a high potential for spills and deployed in a manner
that allows rapid access and use by contractors. Some heavy equipment may have on-
board spill kits for small spills. Spill control kits will be inspected and inventoried each
construction season to confirm all required items are present. Spill control kits will be
inventoried after each emergency event and restocked as needed.
Minor Spills:
· Minor spills typically involve small quantities of oil, gasoline, paint, etc. which can be
controlled at the discovery of the spill.
· Contain the spread of the spill.
· Use absorbent materials on small spills rather than hosing down or burying the spill.
· Notify the project foreman immediately
· Recover spilled materials.
· Clean the contaminated area and properly dispose of contaminated materials.
· If the spill occurs on paved or impermeable surfaces, clean up using "dry" methods
(absorbent materials, cat litter and/or rags). Contain the spill by encircling with absorbent
materials and do not let the spill spread widely.
· If the spill occurs in dirt areas, immediately contain the spill by constructing an earthen
dike. Dig up and properly dispose of contaminated soil.
· If the spill occurs during rain, cover spill with tarps or other material to prevent
contaminating runoff.
Semi-Significant Spills:
· Semi-significant spills still can be controlled by the first responder along with the aid of
other personnel such as laborers and the foreman, etc. This response may require the
cessation of all other activities. Spills should be cleaned up immediately.
Significant/Hazardous Spills
· For significant or hazardous spills that cannot be controlled by personnel in the immediate
vicinity, the following steps should be taken:
o Notify the local emergency response by dialing 911. In addition to 911, the
contractor will notify the proper City or County officials. All emergency phone
numbers will be posted at the construction site.
o Contact your Supervisor and the Divisional Environmental Manager. For spills of
federal reportable quantities, (examples are listed below) in conformance with the
requirements in 40 CFR parts 110,119, and 302, the Division Environmental
Manager (DEM) will notify the National Response Center at (800) 424-8802. The
DEM will notify the Department of Ecology and any other applicable agencies.
· The services of a spills contractor or a Haz-Mat team should be obtained immediately.
Construction personnel should not attempt to clean up until the appropriate and qualified
staffs have arrived at the job site.
· Notification should first be made by telephone and followed up with a written report. Other
agencies which may need to be consulted include, but are not limited to, the Public Works
Department, the Coast Guard, the Highway Patrol, the City/County Police Department and
Department of Ecology.
· Federal regulations require that any significant oil spill into a water body or onto an
adjoining shoreline be reported to the National Response Center (NRC) at 800-424-8802
(24 hours)
Installation Schedules: The described BMPs will be implemented while all pollution generating
materials are onsite.
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work.
Responsible Staff: Certified Erosion and Sediment Control Lead
Will wheel wash or tire bath system BMPs be used during construction?
Yes No
Will pH-modifying sources be present on-site?
Yes No
Table 3 – pH-Modifying Sources
None
Bulk cement
Cement kiln dust
Fly ash
Other cementitious materials
New concrete washing or curing waters
Waste streams generated from concrete grinding and sawing
Exposed aggregate processes
Dewatering concrete vaults
Concrete pumping and mixer washout waters
Recycled concrete
Other (i.e., calcium lignosulfate) [please describe: ]
List and describe BMPs:
· pH Control for High pH Water (BMP C253)
· High pH Neutralization using CO2 (BMP C252) (Implemented only after notifying the local
Jurisdiction.)
· Sawcutting and Surfacing Pollution Prevention (BMP C152)
Sawcutting shall be performed in accordance with this BMP, including proper containment
and disposal of sawcutting slurry.
Installation Schedules: The described BMPs will be implemented while all pollution generating
materials are onsite.
Inspection and Maintenance plan: Inspection and maintenance is to take place at the end of each
day's work and following significant rain events.
Responsible Staff: Certified Erosion and Sediment Control Lead
Adjust pH of stormwater if outside the range of 6.5 to 8.5 su.
Obtain written approval from Ecology before using chemical treatment with the exception of CO2
or dry ice to modify pH.
Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches,
streets, or streams. Excess concrete must not be dumped on-site, except in designated
concrete washout areas with appropriate BMPs installed.
Element 10: Control Dewatering
Dewatering may be required during utility construction, especially during the wet season.
Contaminated water is not anticipated for this site.
Table 4 – Dewatering BMPs
Infiltration
Transport off-site in a vehicle (vacuum truck for legal disposal)
Ecology-approved on-site chemical treatment or other suitable treatment technologies
Sanitary or combined sewer discharge with local sewer district approval (last resort)
Use of sedimentation bag with discharge to ditch or swale (small volumes of localized
dewatering)
List and describe BMPs:
· Vac truck offsite disposal can be used at contractor's option to remove highly turbid
water from the site.
· DOE-approved on-site chemical treatment may be used if other techniques are not
successful.
· Sanitary sewer disposal may be allowed subject to approval by the local sewer district.
· Sedimentation bag with discharge to ditch or swale if volumes of dewatering are small
and high turbidity is not present.
Installation Schedules: One or more of the described BMPs will be implemented at all times
while dewatering activities are being performed.
Inspection and Maintenance plan: Inspection and maintenance is to take place contiuously
during dewatering activity.
Responsible Staff: Certified Erosion and Sediment Control Lead
Element 11: Maintain BMPs
All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained
and repaired as needed to ensure continued performance of their intended function.
Maintenance and repair shall be conducted in accordance with each particular BMP
specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW).
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 ESC BMPs shall be removed within 30 days after final site stabilization is
achieved or after the temporary BMPs are no longer needed.
Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal
of either BMPs or vegetation shall be permanently stabilized.
Additionally, protection must be provided for all BMPs installed for the permanent control of
stormwater from sediment and compaction. BMPs that are to remain in place following
completion of construction shall be examined and restored to full operating condition. If
sediment enters these BMPs during construction, the sediment shall be removed and the facility
shall be returned to conditions specified in the construction documents.
Element 12: Manage the Project
The project will be managed based on the following principles:
· Projects will be phased to the maximum extent practicable and seasonal work limitations
will be taken into account.
· Inspection and monitoring:
o Inspection, maintenance and repair of all BMPs will occur as needed to ensure
performance of their intended function.
o Site inspections and monitoring will be conducted in accordance with Special
Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map.
Sampling station(s) are located in accordance with applicable requirements of
the CSWGP.
· Maintain an updated SWPPP.
o The SWPPP will be updated, maintained, and implemented in accordance with
Special Conditions S3, S4, and S9 of the CSWGP.
As site work progresses the SWPPP will be modified routinely to reflect changing site
conditions. The SWPPP will be reviewed monthly to ensure the content is current.
Table 5 – Management
Design the project to fit the existing topography, soils, and drainage patterns
Emphasize erosion control rather than sediment control
Minimize the extent and duration of the area exposed
Keep runoff velocities low
Retain sediment on-site
Thoroughly monitor site and maintain all ESC measures
Schedule major earthwork during the dry season
Other (please describe)
Element 13: Protect Low Impact Development (LID) BMPs
LID facilities are not proposed for this project. This element is not applicable.
Pollution Prevention Team (3.0)
Table 7 – Team Information
Title Name(s) Phone Number
Certified Erosion and
Sediment Control Lead
(CESCL)
TBD TBD
Resident Engineer Barry Talkington (425) 251-6222
Emergency Ecology
Contact
Staff on Duty (360) 407-6242
Emergency Permittee/
Owner Contact
TBD TBD
Non-Emergency Owner
Contact
Chris Penwell (206) 651-9323
Monitoring Personnel TBD TBD
Ecology Regional Office 3190 160th Ave SE, Bellevue, WA (425) 649-7000
Monitoring and Sampling Requirements (4.0)
Monitoring includes visual inspection, sampling for water quality parameters of concern, and
documentation of the inspection and sampling findings in a site log book. A site log book will be
maintained for all on-site construction activities and will include:
· A record of the implementation of the SWPPP and other permit requirements
· Site inspections
· Stormwater sampling data
The site log book must be maintained on-site within reasonable access to the site and be made
available upon request to Ecology or the local jurisdiction.
Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See
CSWGP Special Condition S8 and Section 5 of this template.
Site Inspection (4.1)
Site inspections will be conducted at least once every calendar week and within 24 hours
following any discharge from the site. For sites that are temporarily stabilized and inactive, the
required frequency is reduced to once per calendar month.
The discharge point(s) are indicated on the Site Map (see Appendix A) and in accordance with
the applicable requirements of the CSWGP.
Stormwater Quality Sampling (4.2)
Turbidity Sampling (4.2.1)
Requirements include calibrated turbidity meter or transparency tube to sample site discharges
for compliance with the CSWGP. Sampling will be conducted at all discharge points at least
once per calendar week.
Method for sampling turbidity:
Table 8 – Turbidity Sampling Method
Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size)
Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size)
The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency
less than 33 centimeters.
If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to
or greater than 6 cm, the following steps will be conducted:
1. Review the SWPPP for compliance with Special Condition S9. Make appropriate
revisions within 7 days of the date the discharge exceeded the benchmark.
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period.
3. Document BMP implementation and maintenance in the site log book.
If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following
steps will be conducted:
1. Telephone or submit an electronic report to the applicable Ecology Region’s
Environmental Report Tracking System (ERTS) within 24 hours.
https://www.ecology.wa.gov/About-us/Get-involved/Report-an-environmental-issue
· Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish,
Whatcom): (425) 649-7000
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period
3. Document BMP implementation and maintenance in the site log book.
4. Continue to sample discharges daily until one of the following is true:
· Turbidity is 25 NTU (or lower).
· Transparency is 33 cm (or greater).
· Compliance with the water quality limit for turbidity is achieved.
o 1 - 5 NTU over background turbidity, if background is less than 50 NTU
o 1% - 10% over background turbidity, if background is 50 NTU or greater
· The discharge stops or is eliminated.
pH Sampling (4.2.2)
pH monitoring is required for “Significant concrete work” (i.e. greater than 1000 cubic yards
poured concrete or recycled concrete over the life of the project).The use of engineered soils
(soil amendments including but not limited to Portland cement-treated base [CTB], cement kiln
dust [CKD] or fly ash) also requires pH monitoring.
For significant concrete work, pH sampling will start the first day concrete is poured and
continue until it is cured, typically three (3) weeks after the last pour.
For engineered soils and recycled concrete, pH sampling begins when engineered soils or
recycled concrete are first exposed to precipitation and continues until the area is fully
stabilized.
If the measured pH is 8.5 or greater, the following measures will be taken:
1. Prevent high pH water from entering storm sewer systems or surface water.
2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate
technology such as carbon dioxide (CO2) sparging (liquid or dry ice).
3. Written approval will be obtained from Ecology prior to the use of chemical treatment
other than CO2 sparging or dry ice.
Method for sampling pH:
Table 8 – pH Sampling Method
pH meter
pH test kit
Wide range pH indicator paper
Discharges to 303(d) or Total Maximum Daily Load (TMDL)
Waterbodies (5.0)
303(d) Listed Waterbodies (5.1)
Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH?
Yes No
List the impairment(s):
This section does not apply.
TMDL Waterbodies (5.2)
Waste Load Allocation for CWSGP discharges:
List and describe BMPs:
This section does not apply.
Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point
of discharge.
Reporting and Record Keeping (6.0)
Record Keeping (6.1)
Site Log Book (6.1.1)
A site log book will be maintained for all on-site construction activities and will include:
· A record of the implementation of the SWPPP and other permit requirements
· Site inspections
· Sample logs
Records Retention (6.1.2)
Records will be retained during the life of the project and for a minimum of three (3) years
following the termination of permit coverage in accordance with Special Condition S5.C of the
CSWGP.
Permit documentation to be retained on-site:
· CSWGP
· Permit Coverage Letter
· SWPPP
· Site Log Book
Permit documentation will be provided within 14 days of receipt of a written request from
Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when
requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP.
Updating the SWPPP (6.1.3)
The SWPPP will be modified if:
· Found ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site.
· There is a change in design, construction, operation, or maintenance at the construction
site that has, or could have, a significant effect on the discharge of pollutants to waters
of the State.
The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine
additional or modified BMPs are necessary for compliance. An updated timeline for BMP
implementation will be prepared.
Reporting (6.2)
Discharge Monitoring Reports (6.2.1)
Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring
Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given
monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR
due date is fifteen (15) days following the end of each calendar month.
DMRs will be reported online through Ecology’s WQWebDMR System.
To sign up for WQWebDMR go to:
https://www.ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Water-quality-
permits-guidance/WQWebPortal-guidance
Notification of Noncompliance (6.2.2)
If any of the terms and conditions of the permit is not met, and the resulting noncompliance may
cause a threat to human health or the environment, the following actions will be taken:
1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable
Regional office ERTS phone number (Regional office numbers listed below).
2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or
correct the noncompliance. If applicable, sampling and analysis of any noncompliance
will be repeated immediately and the results submitted to Ecology within five (5) days of
becoming aware of the violation.
3. A detailed written report describing the noncompliance will be submitted to Ecology
within five (5) days, unless requested earlier by Ecology.
Specific information to be included in the noncompliance report is found in Special Condition
S5.F.3 of the CSWGP.
Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6
cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as
required by Special Condition S5.A of the CSWGP.
· Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit,
Snohomish, or Whatcom County
Include the following information:
1. Your name and / Phone number
2. Permit number
3. City / County of project
4. Sample results
5. Date / Time of call
6. Date / Time of sample
7. Project name
In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will
be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH
water.
Appendix/Glossary
A. Site Map
B. BMP Detail
C. Correspondence
D. Site Inspection Form
Create your own or download Ecology’s template:
https://www.ecology.wa.gov/Regulations-Permits/Permits-certifications/Stormwater-
general-permits/Construction-stormwater-permit
E. Construction Stormwater General Permit (CSWGP)
F. 303(d) List Waterbodies / TMDL Waterbodies Information
Not applicable to this project
G. Contaminated Site Information
Not applicable to this project
H. Engineering Calculations
Not applicable to this project
Appendix A:
Site Map
Title:For:
12
7708 CHRIS PENWELL
696 MOSS FARM ROAD
CHESHIRE, CT 06410 PENWELL PROPERTYFORCITY OF FEDERAL WAY, KING COUNTY, WASHINGTONPTN. OF THE SE 1/4, OF THE NE 1/4, SEC. 06, TWP 21 N., RGE 04 E., W.M.FOR
PENWELL PROPERTYCALL BEFORE YOU DIG: 8118/3
/2
3 TESC PLAN11
TESC PLANSCALE: 1"=20'2ND AV
E
S
W
TEMPORARY "V" DITCHROCK CHECK DAM DETAILCHECK DAM SPACINGRECOMMENDED CONSTRUCTION SEQUENCEFILTER FABRIC SILT FENCE DETAILTABLE D.3.2.B TEMPORARY EROSION CONTROL SEED MIXTEMPORARY SEEDING STANDARDS AND SPECIFICATIONSSEEDING NOTESLEGEND:EROSION/SEDIMENT CONTROL NOTES
Appendix B:
BMP Details
SECTION D.2.1 ESC MEASURES
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D-10
D.2.1 ESC MEASURES
This section details the ESC measures that are required to minimize erosion and sediment transport off a
construction site and protect areas of existing and proposed flow control BMPs. These ESC measures
represent Best Management Practices (BMPs)6 for the control of erosion and entrained sediment as well as
other impacts related to construction such as increased runoff due to land disturbing activities. The
measures and practices are grouped into nine sections corresponding to each of the nine categories of ESC
measures in Core Requirement #5, Section 1.2.5 of the King County Surface Water Design Manual. The
introductory paragraphs at the beginning each section present the basic requirement for that category of
measures, the purpose of those measures, installation requirements relative to construction activity,
guidelines for the conditions of use, and other information relevant to all measures in the section/category.
Compliance with each of the nine categories of the ESC measures, to the extent applicable and necessary
to meet the performance criteria in Section D.2.1, and compliance with the ESC implementation
requirements in Section D.2.4, constitutes overall compliance with King County's ESC Standards.
Note: Additional measures shall be required by the County if the existing standards are insufficient to
protect adjacent properties, drainage facilities, or water resources.
The standards for each individual ESC measure are divided into four sections:
1. Purpose
2. Conditions of Use
3. Design and Installation Specifications
4. Maintenance Requirements.
A code and symbol for each measure have also been included for ease of use on ESC plans. Note that the
"Conditions of Use" always refers to site conditions. As site conditions change, ESC measures must be
changed to remain in compliance with the requirements of this appendix.
Whenever compliance with King County ESC Standards is required, all of the following categories of
ESC measures must be considered for application to the project site as detailed in the following sections:
1. Clearing Limits: Prior to any site clearing or grading, areas to remain undisturbed during project
construction shall be delineated on the project's ESC plan and physically marked on the project site.
2. Cover Measures: Temporary and permanent cover measures shall be provided when necessary to
protect disturbed areas. The intent of these measures is to prevent erosion by having as much area as
possible covered during any period of precipitation.
3. Perimeter Protection: Perimeter protection to filter sediment from sheet flow shall be provided
downstream of all disturbed areas prior to upslope grading.
4. Traffic Area Stabilization: Unsurfaced entrances, roads, and parking areas used by construction
traffic shall be stabilized to minimize erosion and tracking of sediment offsite.
5. Sediment Retention: Surface water collected from all disturbed areas of the site shall be routed
through a sediment pond or trap prior to release from the site, except those areas at the perimeter of
the site small enough to be treated solely with perimeter protection. Sediment retention facilities shall
be installed prior to grading any contributing area.
6. Surface Water Collection: Surface water collection measures (e.g., ditches, berms, etc.) shall be
installed to intercept all surface water from disturbed areas, convey it to a sediment pond or trap, and
discharge it downstream of any disturbed areas. Areas at the perimeter of the site, which are small
enough to be treated solely with perimeter protection, do not require surface water collection.
6 Best Management Practices (BMPs) means the best available and reasonable physical, structural, managerial, or behavioral
activities, that when singly or in combination, eliminate or reduce the contamination of surface and/or ground waters.
D.2.1.1 CLEARING LIMITS
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D-11
Significant sources of upstream surface water that drain onto disturbed areas shall be intercepted and
conveyed to a stabilized discharge point downstream of the disturbed areas. Surface water collection
measures shall be installed concurrently with or immediately following rough grading and shall be
designed, constructed, and stabilized as needed to minimize erosion.
7. Dewatering Control: The water resulting from construction site de-watering activities must be
treated prior to discharge or disposed of as specified.
8. Dust Control: Preventative measures to minimize wind transport of soil shall be implemented when a
traffic hazard may be created or when sediment transported by wind is likely to be deposited in water
resources.
9. Flow Control: Surface water from disturbed areas must be routed through the project's onsite flow
control facility or other provisions must be made to prevent increases in the existing site conditions 2-
year and 10-year runoff peaks discharging from the project site during construction (flow control
BMP areas (existing or proposed) shall not be used for this purpose).
10. Control Pollutants: Stormwater pollution prevention (SWPPS) measures are required to prevent,
reduce, or eliminate the discharge of pollutants to onsite or adjacent stormwater systems or
watercourses from construction-related activities such as materials delivery and storage, onsite
equipment fueling and maintenance, demolition of existing buildings and disposition of demolition
materials and other waste, and concrete handling, washout and disposal. Section D.2.2 describes
BMPs specific to this purpose; additionally, several of the ESC BMPs described herein are applicable.
11. Protect Existing and Proposed Flow Control BMPs: Sedimentation and soil compaction reduce the
infiltration capacity of native and engineered soils. Protection measures shall be applied/installed and
maintained so as to prevent adverse impacts to existing flow control BMPs and areas of proposed flow
control BMPs for the project. Adverse impacts can prompt the requirement to restore or replace
affected BMPs.
12. Maintain BMPs: Protection measures shall be maintained to assure continued performance of their
intended function, to prevent adverse impacts to existing flow control BMPs and areas of proposed
flow control BMPs, and protect other disturbed areas of the project.
13. Manage the Project: Coordination and timing of site development activities relative to ESC
concerns, and timely inspection, maintenance and update of protective measures are necessary to
effectively manage the project and assure the success of protective ESC and SWPPS design and
implementation.
D.2.1.1 CLEARING LIMITS
Prior to any site clearing or grading, those areas that are to remain undisturbed during project construction
shall be delineated. At a minimum, clearing limits shall be installed at the edges of all critical area buffers
and any other areas required to be left uncleared such as portions of the site subject to clearing limits under
KCC 16.82.150, areas around significant trees identified to be retained, flow control BMP areas to be
protected, and other areas identified to be left undisturbed to protect sensitive features.
Purpose: The purpose of clearing limits is to prevent disturbance of those areas of the project site that are
not designated for clearing or grading. This is important because limiting site disturbance is the single
most effective method for reducing erosion. Clearing limits may also be used to control construction
traffic, thus reducing the disturbance of soil and limiting the amount of sediment tracked off site.
When to Install: Clearing limits shall be installed prior to the clearing and/or grading of the site.
Measures to Use: Marking clearing limits by delineating the site with a continuous length of brightly
colored survey tape is sometimes sufficient. The tape may be supported by vegetation or stakes, and it
shall be 3 to 6 feet high and highly visible. Critical areas and their buffers require more substantial
protection and shall be delineated with plastic or metal safety fences or stake and wire fences. Fencing
may be required at the County's discretion to control construction traffic or at any location where greater
SECTION D.2.1 ESC MEASURES
7/23/2021 2021 Surface Water Design Manual – Appendix D
D-12
protection is warranted. Permanent fencing may also be used if desired by the applicant. Silt fence, in
combination with survey flagging, is also an acceptable method of marking critical areas and their
buffers.
D.2.1.1.1 PLASTIC OR METAL FENCE
Code: FE Symbol:
Purpose
Fencing is intended to (1) restrict clearing to approved limits; (2) prevent disturbance of critical areas, their
buffers, and other areas required to be left undisturbed; (3) limit construction traffic to designated
construction entrances or roads; and (4) protect areas where marking with survey tape may not provide
adequate protection.
Conditions of Use
To establish clearing limits, plastic or metal fence may be used:
1. At the boundary of critical areas, their buffers, and other areas required to be left uncleared.
2. As necessary to control vehicle access to and on the site (see Sections D.2.1.4.1 and D.2.1.4.2).
Design and Installation Specifications
1. The fence shall be designed and installed according to the manufacturer's specifications.
2. The fence shall be at least 3 feet high and must be highly visible.
3. The fence shall not be wired or stapled to trees.
Maintenance Requirements
1. If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and
visibility restored.
2. Disturbance of a critical area, critical area buffer, native growth retention area, or any other area
required to be left undisturbed shall be reported to the County for resolution.
D.2.1.2 COVER MEASURES
Temporary and permanent cover measures shall be provided to protect all disturbed areas, including the
faces of cut and fill slopes. Temporary cover shall be installed if an area is to remain unworked for more
than seven days during the dry season (May 1 to September 30) or for more than two consecutive working
days during the wet season (October 1 to April 30). These time limits may be relaxed if an area poses a
low risk of erosion due to soil type, slope gradient, anticipated weather conditions, or other factors.
Conversely, the County may reduce these time limits if site conditions warrant greater protection (e.g.,
adjacent to significant aquatic resources or highly erosive soils) or if significant precipitation (see Section
D.2.4.2) is expected. Any area to remain unworked for more than 30 days shall be seeded or sodded,
unless the County determines that winter weather makes vegetation establishment infeasible. During the
wet season, slopes and stockpiles at 3H:1V or steeper and with more than ten feet of vertical relief shall be
covered if they are to remain unworked for more than 12 hours. Also during the wet season, the material
necessary to cover all disturbed areas must be stockpiled on site. The intent of these cover requirements is
to have as much area as possible covered during any period of precipitation.
Purpose: The purpose of covering exposed soils is to prevent erosion, thus reducing reliance on less
effective methods that remove sediment after it is entrained in runoff. Cover is the only practical method
of reducing turbidity in runoff. Structural measures, such as silt fences and sediment ponds, are only
capable of removing coarse particles and in most circumstances have little to no effect on turbidity.
SECTION D.2.1 ESC MEASURES
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D.2.1.2.2 MULCHING
Code: MU Symbol:
Purpose
The purpose of mulching soils is to provide 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 is an enormous variety of mulches that may be used. Only the most
common types are discussed in this section.
Conditions of Use
As a temporary cover measure, mulch should be used:
1. On disturbed areas that require cover measures for less than 30 days
2. As a cover for seed during the wet season and during the hot summer months
3. During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical relief.
Design and Installation Specifications
For mulch materials, application rates, and specifications, see Table D.2.1.2.A. Note: Thicknesses may be
increased for disturbed areas in or near critical areas or other areas highly susceptible to erosion.
Maintenance Standards
1. The thickness of the cover must be maintained.
2. 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 drainage problem shall be assessed and alternate drainage
such as interceptor swales may be needed to fix the problem and the eroded area remulched.
D.2.1.2 COVER MEASURES
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D-17
TABLE D.2.1.2.A MULCH STANDARDS AND GUIDELINES
Mulch
Material
Quality Standards Application Rates Remarks
Straw Air-dried; free from
undesirable seed and
coarse material
2"-3" thick; 5 bales
per 1000 sf or 2-3
tons per acre
Cost-effective protection when applied with adequate
thickness. Hand-application generally requires
greater thickness than blown straw. Straw should be
crimped to avoid wind blow. The thickness of straw
may be reduced by half when used in conjunction
with seeding.
Wood Fiber
Cellulose
No growth inhibiting
factors
Approx. 25-30 lbs
per 1000 sf or
1500-2000 lbs per
acre
Shall be applied with hydromulcher. Shall not be
used without seed and tackifier unless the application
rate is at least doubled. Some wood fiber with very
long fibers can be effective at lower application rates
and without seed or tackifier.
Compost No visible water or
dust during handling.
Must be purchased
from supplier with
Solid Waste Handling
Permit.
2" thick min.;
approx. 100 tons
per acre (approx.
1.5 cubic feet per
square yard)
More effective control can be obtained by increasing
thickness to 3" (2.25 cubic feet per square yard).
Excellent mulch for protecting final grades until
landscaping because it can be directly seeded or
tilled into soil as an amendment. Compost may not
be used in Sensitive Lake7 basins unless analysis of
the compost shows no phosphorous release.
Hydraulic
Matrices
(Bonded
Fiber Matrix)
This mulch category
includes hydraulic
slurries composed of
wood fiber, paper fiber
or a combination of
the two held together
by a binding system.
The BFM shall be a
mixture of long wood
fibers and various
bonding agents.
Apply at rates from
3,000 lbs per acre
to 4,000 lbs per
acre and based on
manufacturers
recommendations
The BFM shall not be applied immediately before,
during or immediately after rainfall so that the matrix
will have an opportunity to dry for 24 hours after
installation. Application rates beyond 2,500 pounds
may interfere with germination and are not usually
recommended for turf establishment. BFM is
generally a matrix where all fiber and binders are in
one bag, rather than having to mix components from
various manufacturers to create a matrix. BFMs can
be installed via helicopter in remote areas. They are
approximately $1,000 per acre cheaper to install.
Chipped Site
Vegetation
Average size shall be
several inches.
2" minimum
thickness
This is a cost-effective way to dispose of debris from
clearing and grubbing, and it eliminates the problems
associated with burning. Generally, it should not be
used on slopes above approx. 10% because of its
tendency to be transported by runoff. It is not
recommended within 200 feet of surface waters. If
seeding is expected shortly after mulch, the
decomposition of the chipped vegetation may tie up
nutrients important to grass establishment.
7 Sensitive lake means a lake that has proved to be particularly prone to eutrophication; the County gives this designation when
an active input plan has been adopted to limit the amount of phosphorous entering the lake.
SECTION D.2.1 ESC MEASURES
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D.2.1.2.3 NETS AND BLANKETS
Code: NE Symbol:
Purpose
Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on
steep slopes and in channels so that vegetation can become well established. In addition, some nets and
blankets can be used to permanently reinforce turf to protect drainage ways during high flows. Nets are
strands of material woven into an open, but high-tensile strength net (for example, jute matting). Blankets
are strands of material that are not tightly woven, but instead form a layer of interlocking fibers, typically
held together by a biodegradable or photodegradable netting (for example, excelsior or straw blankets).
They generally have lower tensile strength than nets, but cover the ground more completely. Coir
(coconut fiber) fabric comes as both nets and blankets.
Conditions of Use
Erosion control nets and blankets should be used:
1. For permanent stabilization of slopes 2H:1V or greater and with more than 10 feet of vertical relief.
2. In conjunction with seed for final stabilization of a slope, not for temporary cover. However, they
may be used for temporary applications as long as the product is not damaged by repeated handling.
In fact, this method of slope protection is superior to plastic sheeting, which generates high-velocity
runoff (see Section D.2.1.2.4).
3. For drainage ditches and swales (highly recommended). The application of appropriate netting or
blanket to drainage ditches and swales can protect bare soil from channelized runoff while vegetation
is established. Nets and blankets also can capture a great deal of sediment due to their open, porous
structure. Synthetic nets and blankets may be used to permanently stabilize channels and may provide
a cost-effective, environmentally preferable alternative to riprap.
Design and Installation Specifications
1. See Figure D.2.1.2.B and Figure D.2.1.2.C for typical orientation and installation of nettings and
blankets. Note: Installation is critical to the effectiveness of these products. If good ground contact is
not achieved, runoff can concentrate under the product, resulting in significant erosion.
2. With the variety of products available, it is impossible to cover all the details of appropriate use and
installation. Therefore, it is critical that the design engineer thoroughly consults the manufacturer's
information and that a site visit takes place in order to insure that the product specified is appropriate.
3. Jute matting must be used in conjunction with mulch (Section D.2.1.2.2). Excelsior, woven straw
blankets, and coir (coconut fiber) blankets may be installed without mulch. There are many other
types of erosion control nets and blankets on the market that may be appropriate in certain
circumstances. Other types of products will have to be evaluated individually. In general, most nets
(e.g., jute matting) require mulch in order to prevent erosion because they have a fairly open structure.
Blankets typically do not require mulch because they usually provide complete protection of the
surface.
4. Purely synthetic blankets are allowed but shall only be used for long-term stabilization of waterways.
The organic blankets authorized above are better for slope protection and short-term waterway
protection because they retain moisture and provide organic matter to the soil, substantially improving
the speed and success of re-vegetation.
Maintenance Standards
1. Good contact with the ground must be maintained, and there must not be erosion beneath the net or
D.2.1.2 COVER MEASURES
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D-19
blanket.
2. Any areas of the net or blanket that are damaged or not in close contact with the ground shall be
repaired and stapled.
3. If erosion occurs due to poorly controlled drainage, the problem shall be fixed and the eroded area
protected.
FIGURE D.2.1.2.B WATERWAY INSTALLATION
•DO NOT STRETCH BLANKETS/MATTINGS TIGHT - ALLOW THE ROLLS
TO MOLD TO ANY IRREGULARITIES.
•SLOPE SURFACE SHALL BE SMOOTH BEFORE PLACEMENT FOR
PROPER SOIL CONTACT.
•ANCHOR, STAPLE, AND INSTALL CHECK SLOTS AS PER
MANUFACTURER'S RECOMMENDATIONS.
•AVOID JOINING MATERIAL IN THE CENTER OF THE DITCH.
•LIME, FERTILIZE AND SEED BEFORE INSTALLATION.
MIN.4" OVERLAP'
MIN.6"
OVERLAP
FIGURE D.2.1.2.C SLOPE INSTALLATION
SLOPE SURFACE SHALL BE SMOOTH BEFORE
PLACEMENT FOR PROPER SOIL CONTACT
STAPLING PATTERN AS PER
MANUFACTURER'S RECOMMENDATION
MIN. 2" OVERLAP
LIME, FERTILIZE AND SEED BEFORE
INSTALLATION. PLANTING OF SHRUBS, TREES,
ETC. SHOULD OCCUR AFTER INSTALLATION
DO NOT STRETCH BLANKETS/MATTINGS TIGHT - ALLOW
THE ROLLS TO MOLD TO ANY IRREGULARITIES
FOR SLOPES LESS THAN 3H:1V, ROLLS MAY BE PLACED
IN HORIZONTAL STRIPS
BRING MATERIAL DOWN TO A LEVEL
AREA, TURN THE END UNDER 4" AND
STAPLE AT 12" INTERVALS
ANCHOR IN 6"x6" MIN.
TRENCH AND STAPLE
AT 12" INTERVALS
STAPLE OVERLAPS
MAX. 5' SPACING
IF THERE IS A BERM AT THE
TOP OF SLOPE, ANCHOR
UPSLOPE OF THE BERM
MIN. 6" OVERLAP
SECTION D.2.1 ESC MEASURES
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D.2.1.2.4 PLASTIC COVERING
Code: PC Symbol:
Purpose
Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas.
Conditions of Use
1. Plastic covering may be used on disturbed areas that require cover measures for less than 30 days.
2. Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively
rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term applications.
3. Clear plastic sheeting may be used over newly-seeded areas to create a greenhouse effect and
encourage grass growth. Clear plastic should not be used for this purpose during the summer months
because the resulting high temperatures can kill the grass.
4. Due to rapid runoff caused by plastic sheeting, this method shall not be used upslope of areas that
might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes.
Note: There have been many problems with plastic, usually attributable to poor installation and
maintenance. However, the material itself can cause problems, even when correctly installed and
maintained, because it generates high-velocity runoff and breaks down quickly due to ultraviolet
radiation. In addition, if the plastic is not completely removed, it can clog drainage system inlets and
outlets. It is highly recommended that alternatives to plastic sheeting be used whenever possible and that
its use be limited.
Design and Installation Specifications
1. See Figure D.2.1.2.D for details.
2. Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
3. If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be
installed at the toe of the slope in order to reduce the velocity of runoff.
FIGURE D.2.1.2.D PLASTIC COVERING
TIRES, SANDBAGS, OR
EQUIVALENT MAY BE USED
TO WEIGHT PLASTIC
SEAMS BETWEEN SHEETS
MUST OVERLAP A MINIMUM
OF 12" AND BE WEIGHTED
OR TAPED
TOE IN SHEETING
IN MINIMUM 4"X4"
TRENCH
PROVIDE ENERGY DISSIPATION
AT TOE WHEN NEEDED
10' MAX.
10' MAX.
D.2.1.2 COVER MEASURES
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D-21
Maintenance Standards for Plastic Covering
1. Torn sheets must be replaced and open seams repaired.
2. If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely removed and
replaced.
3. When the plastic is no longer needed, it shall be completely removed.
D.2.1.2.5 STRAW WATTLES
Code: SW Symbol:
Purpose
Wattles are erosion and sediment control barriers consisting of straw wrapped in biodegradable tubular
plastic or similar encasing material. Wattles may reduce the velocity and can spread the flow of rill and
sheet runoff, and can capture and retain sediment. Straw wattles are typically 8 to 10 inches in diameter
and 25 to 30 feet in length. The wattles are placed in shallow trenches and staked along the contour of
disturbed or newly constructed slopes.
Conditions of Use
1. Install on disturbed areas that require immediate erosion protection.
2. Use on slopes requiring stabilization until permanent vegetation can be established.
3. Can be used along the perimeter of a project, as a check dam in unlined ditches and around temporary
stockpiles
4. Wattles can be staked to the ground using willow cuttings for added revegetation.
5. Rilling can occur beneath and between wattles if not properly entrenched, allowing water to pass
below and between wattles
Design and Installation Specifications
1. It is critical that wattles are installed perpendicular to the flow direction and parallel to the slope
contour.
2. Narrow trenches should be dug across the slope, on contour, to a depth of 3 to 5 inches on clay soils
and soils with gradual slopes. On loose soils, steep slopes, and during high rainfall events, the
trenches should be dug to a depth of 5 to 7 inches, or ½ to 2/3 of the thickness of the wattle.
3. Start construction of trenches and installing wattles from the base of the slope and work uphill.
Excavated material should be spread evenly along the uphill slope and compacted using hand tamping
or other method. Construct trenches at contour intervals of 3 to 30 feet apart depending on the
steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches
should be constructed.
4. Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends.
5. Install stakes at each end of the wattle, and at 4 foot centers along the entire length of the wattle.
6. If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and
into the soil.
7. At a minimum, wooden stakes should be approximately ¾ x ¾ x 24 inches. Willow cuttings or 3/8
inch rebar can also be used for stakes.
SECTION D.2.1 ESC MEASURES
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D-22
8. Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding
above the wattle.
Maintenance Standards
1. Inspect wattles prior to forecasted rain, daily during extended rain events, after rain events, weekly
during the wet season, and at two week intervals at all other times of the year.
2. Repair or replace split, torn, raveling, or slumping wattles
3. Remove sediment accumulations when exceeding ½ the height between the top of the wattle and the
ground surface.
D.2.1.2 COVER MEASURES
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D-23
FIGURE D.2.1.2.E STRAW WATTLES
1.STRAW ROLL INSTALLATION REQUIRES THE PLACEMENT AND SECURE STAKING
OF THE ROLL IN A TRENCH, 3" x 5" (75-125mm) DEEP, DUG ON CONTOUR.
2.RUNOFF MUST NOT BE ALLOWED TO RUN UNDER OR AROUND ROLL.
ROLL SPACING DEPENDS ON SOIL
TYPE AND SLOPE STEEPNESS
STRAW ROLLS MUST BE PLACED
ALONG SLOPE CONTOURS
3'-4'
(1.2m)
10'-25'
(3-8m)
3"-5"
(75-125mm)
ADJACENT ROLLS
SHALL TIGHTLY ABUT
SEDIMENT, ORGANIC MATTER,
AND NATIVE SEEDS ARE
CAPTURED BEHIND THE ROLLS
LIVE STAKE
1" x 1" STAKE
8"-10" DIA.
(200-250mm)
NOTES:
STRAW WATTLES
NTS
SECTION D.2.1 ESC MEASURES
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D.2.1.2.6 TEMPORARY AND PERMANENT SEEDING
Code: SE Symbol:
Purpose
Seeding is intended to reduce erosion by stabilizing exposed soils. A well-established vegetative cover is
one of the most effective methods of reducing erosion.
Conditions of Use
1. Seeding shall be used throughout the project on disturbed areas that have reached final grade or that
will remain unworked for more than 30 days.
2. Vegetation-lined channels shall be seeded. Channels that will be vegetated should be installed
before major earthwork and hydroseeded or covered with a Bonded Fiber Matrix (BFM).
3. Retention/detention ponds shall be seeded as required.
4. At the County's discretion, seeding without mulch during the dry season is allowed even though it
will take more than seven days to develop an effective cover. Mulch is, however, recommended at all
times because it protects seeds from heat, moisture loss, and transport due to runoff.
5. At the beginning of the wet season, all disturbed areas shall be reviewed to identify which ones can be
seeded in preparation for the winter rains (see Section D.2.4.2). Disturbed areas shall be seeded
within one week of the beginning of the wet season. A sketch map of those areas to be seeded and
those areas to remain uncovered shall be submitted to the DLS-Permitting inspector. The DLS-
Permitting inspector may require seeding of additional areas in order to protect surface waters,
adjacent properties, or drainage facilities.
6. At final site stabilization, all disturbed areas not otherwise vegetated or stabilized shall be seeded and
mulched (see Section D.2.4.5).
Design and Installation Specifications
1. The best time to seed is April 1 through June 30, and September 1 through October 15. Areas may be
seeded between July 1 and August 31, but irrigation may be required in order to grow adequate cover.
Areas may also be seeded during the winter months, but it may take several months to develop a dense
groundcover due to cold temperatures. The application and maintenance of mulch is critical for
winter seeding.
2. To prevent seed from being washed away, confirm that all required surface water control measures
have been installed.
3. The seedbed should be firm but not compacted because soils that are well compacted will not vegetate
as quickly or thoroughly. Slopes steeper than 3H:1V shall be surface roughened. Roughening can be
accomplished in a variety of ways, but the typical method is track walking, or driving a crawling
tractor up and down the slope, leaving cleat imprints parallel to the slope contours.
4. In general, 10-20-20 N-P-K (nitrogen-phosphorus-potassium) fertilizer may be used at a rate of 90
pounds per acre. Slow-release fertilizers are preferred because they are more efficient and have fewer
environmental impacts. It is recommended that areas being seeded for final landscaping conduct soil
tests to determine the exact type and quantity of fertilizer needed. This will prevent the over-
application of fertilizer. Disturbed areas within 200 feet of water bodies and wetlands must use slow-
release low-phosphorus fertilizer (typical proportions 3-1-2 N-P-K).
5. The following requirements apply to mulching:
a) Mulch is always required for seeding slopes greater than 3H:1V (see Section D.2.1.2.2).
D.2.1.2 COVER MEASURES
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D-25
b) If seeding during the wet season, mulch is required.
c) The use of mulch may be required during the dry season at the County's discretion if grass growth
is expected to be slow, the soils are highly erodible due to soil type or gradient, there is a water
body close to the disturbed area, or significant precipitation (see Section D.2.4.2) is anticipated
before the grass will provide effective cover.
d) Mulch may be applied on top of the seed or simultaneously by hydroseeding.
6. Hydroseeding is allowed as long as tackifier is included. Hydroseeding with wood fiber mulch is
adequate during the dry season. During the wet season, the application rate shall be doubled because
the mulch and tackifier used in hydroseeding break down fairly rapidly. It may be necessary in some
applications to include straw with the wood fiber, but this can be detrimental to germination.
7. Areas to be permanently landscaped shall use soil amendments. Good quality topsoil shall be tilled
into the top six inches to reduce the need for fertilizer and improve the overall soil quality. Most
native soils will require the addition of four inches of well-rotted compost to be tilled into the soil to
provide a good quality topsoil. Compost used should meet specifications provided in Reference 11-C
of the SWDM.
8. The seed mixes listed below include recommended mixes for both temporary and permanent seeding.
These mixes, with the exception of the wetland mix, shall be applied at a rate of 120 pounds per acre.
This rate may be reduced if soil amendments or slow-release fertilizers are used. Local suppliers
should be consulted for their recommendations because the appropriate mix depends on a variety of
factors, including exposure, soil type, slope, and expected foot traffic. Alternative seed mixes
approved by the County may be used.
Table D.2.1.2.B presents the standard mix for those areas where just a temporary vegetative cover is
required.
TABLE D.2.1.2.B TEMPORARY EROSION CONTROL SEED MIX
% Weight % Purity % Germination
Chewings or red fescue
Festuca rubra var. commutata or
Festuca rubra
40 98 90
Annual or perennial rye
Lolium multiflorum or Lolium perenne
40 98 90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis
10 92 85
White dutch clover
Trifolium repens
10 98 90
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Table D.2.1.2.C provides just one recommended possibility for landscaping seed.
TABLE D.2.1.2.C LANDSCAPING SEED MIX
% Weight % Purity % Germination
Perennial rye blend
Lolium perenne
70 98 90
Chewings and red fescue blend
Festuca rubra var. commutata or
Festuca rubra
30 98 90
This turf seed mix in Table D.2.1.2.D is for dry situations where there is no need for much water. The
advantage is that this mix requires very little maintenance.
TABLE D.2.1.2.D LOW-GROWING TURF SEED MIX
% Weight % Purity % Germination
Dwarf tall fescue (several varieties)
Festuca arundinacea var.
45 98 90
Dwarf perennial rye (Barclay)
Lolium perenne var. barclay
30 98 90
Red fescue
Festuca rubra
20 98 90
Colonial bentgrass
Agrostis tenuis
5 98 90
Table D.2.1.2.E presents a mix recommended for bioswales and other intermittently wet areas. Sod shall
generally not be used for bioswales because the seed mix is inappropriate for this application. Sod may be
used for lining ditches to prevent erosion, but it will provide little water quality benefit during the wet
season.
TABLE D.2.1.2.E BIOSWALE SEED MIX*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or
Festuca elatior
75-80 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 92 85
Redtop bentgrass
Agrostis alba or Agrostis gigantea
5-10 90 80
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
D.2.1.2 COVER MEASURES
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The seed mix shown in Table D.2.1.2.F is a recommended low-growing, relatively non-invasive seed mix
appropriate for very wet areas that are not regulated wetlands (if planting in wetland areas, see Section
6.3.1 of the King County Surface Water Design Manual). Other mixes may be appropriate, depending on
the soil type and hydrology of the area. Apply this mixture at a rate of 60 pounds per acre.
TABLE D.2.1.2.F WET AREA SEED MIX*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or
Festuca elatior
60-70 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 98 85
Meadow foxtail
Alepocurus pratensis
10-15 90 80
Alsike clover
Trifolium hybridum
1-6 98 90
Redtop bentgrass
Agrostis alba
1-6 92 85
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
The meadow seed mix in Table D.2.1.2.G is recommended for areas that will be maintained infrequently
or not at all and where colonization by native plants is desirable. Likely applications include rural road
and utility right-of -way. Seeding should take place in September or very early October in order to obtain
adequate establishment prior to the winter months. The appropriateness of clover in the mix may need to
be considered as this can be a fairly invasive species. If the soil is amended, the addition of clover may
not be necessary.
TABLE D.2.1.2.G MEADOW SEED MIX
% Weight % Purity % Germination
Redtop or Oregon bentgrass
Agrostis alba or Agrostis oregonensis
40 92 85
Red fescue
Festuca rubra
40 98 90
White dutch clover
Trifolium repens
20 98 90
Maintenance Standards for Temporary and Permanent Seeding
1. Any seeded areas that fail to establish at least 80 percent cover within one month shall be reseeded. If
reseeding is ineffective, an alternate method, such as sodding or nets/blankets, shall be used. If winter
weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the County
when critical areas would otherwise be protected.
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2. After adequate cover is achieved, any areas that experience erosion shall be re-seeded and protected
by mulch. If the erosion problem is drainage related, the problem shall be fixed and the eroded area
re-seeded and protected by mulch.
3. Seeded areas shall be supplied with adequate moisture, but not watered to the extent that it causes
runoff.
D.2.1.2.7 SODDING
Code: SO Symbol:
Purpose
The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize
drainage ways where concentrated overland flow will occur.
Conditions of Use
Sodding may be used in the following areas:
1. Disturbed areas that require short-term or long-term cover
2. Disturbed areas that require immediate vegetative cover
3. All waterways that require vegetative lining (except biofiltration swales—the seed mix used in most
sod is not appropriate for biofiltration swales). Waterways may also be seeded rather than sodded,
and protected with a net or blanket (see Section D.2.1.2.3).
Design and Installation Specifications
Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root
mat for mechanical strength.
The following steps are recommended for sod installation:
1. Shape and smooth the surface to final grade in accordance with the approved grading plan.
2. Amend four inches (minimum) of well-rotted compost into the top eight inches of the soil if the
organic content of the soil is less than ten percent. Compost used shall meet compost specifications
per SWDM Reference 11-C.
3. Fertilize according to the supplier's recommendations. Disturbed areas within 200 feet of water
bodies and wetlands must use non-phosphorus fertilizer.
4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface.
5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water
flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit.
Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V.
6. Roll the sodded area and irrigate.
7. When sodding is carried out in alternating strips or other patterns, seed the areas between the sod
immediately after sodding.
Maintenance Standards
If the grass is unhealthy, the cause shall be determined and appropriate action taken to reestablish a
healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation,
instability, or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and
protected with a net or blanket.
D.2.1.2 COVER MEASURES
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D.2.1.2.8 POLYACRYLAMIDE FOR SOIL EROSION PROTECTION
Purpose
Polyacrylamide (PAM) is used on construction sites to prevent soil erosion. Applying PAM to bare soil in
advance of a rain event significantly reduces erosion and controls sediment in two ways. First, PAM
increases the soil's available pore volume, thus increasing infiltration through flocculation and reducing
the quantity of stormwater runoff. Second, it increases flocculation of suspended particles and aids in their
deposition, thus reducing stormwater runoff turbidity and improving water quality.
Conditions of Use
1. PAM shall not be directly applied to water or allowed to enter a water body.
2. PAM may be applied to wet soil, but dry soil is preferred due to less sediment loss.
3. PAM will work when applied to saturated soil but is not as effective as applications to dry or damp
soil.
4. PAM may be applied only to the following types of bare soil areas that drain to a sediment trap or a
sediment pond:
• Staging areas
• Stockpiles
• Pit sites
• Balanced cut and fill earthwork
• Haul roads prior to placement of crushed rock surfacing
• Compacted soil road base
5. PAM may be applied only during the following phases of construction:
• During rough grading operations
• After final grade and before paving or final seeding and planting
• During a winter shut down of site work. In the case of winter shut down, or where soil will
remain unworked for several months, PAM should be used together with mulch.
6. Do not use PAM on a slope that flows directly to a stream or wetland. The stormwater runoff shall
pass through a sediment control measure prior to discharging to surface waters.
Design and Installation Specifications
1. PAM must be applied using one of two methods of application, "preferred" or "alternative." The
specifications for these methods are described under separate headings below.
2. PAM may be applied in dissolved form with water, or it may be applied in dry, granular or powdered
form. The preferred application method is the dissolved form.
3. PAM is to be applied at a maximum rate of ½ pound PAM per 1000 gallons of water per 1 acre of
bare soil. Table D.2.1.2.H may be used to determine the PAM and water application rate for disturbed
soil areas. Higher concentrations of PAM do not provide any additional effectiveness.
4. Do not add PAM to water discharging from the site.
5. PAM shall be used in conjunction with other ESC measures and not in place of them. When the total
drainage area is greater than or equal to 3 acres, PAM treated areas shall drain to a sediment pond per
Section D.2.1.5.2. For drainage areas less than 3 acres, PAM treated areas must drain to a sediment
trap per Section D.2.1.5.1. Other normally required sediment control measures such as perimeter
SECTION D.2.1 ESC MEASURES
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protection measures (Section D.2.1.3) and surface water collection measures (Section D.2.1.6) shall be
applied to PAM treated areas.
6. All areas not being actively worked shall be covered and protected from rainfall. PAM shall not be
the only cover BMP used.
7. Keep the granular PAM supply out of the sun. Granular PAM loses its effectiveness in three months
after exposure to sunlight and air.
8. Care must be taken to prevent spills of PAM powder onto paved surfaces. PAM, combined with
water, is very slippery and can be a safety hazard. During an application of PAM, prevent over-spray
from reaching pavement as the pavement will become slippery. If PAM powder gets on skin or
clothing, wipe it off with a rough towel rather than washing with water. Washing with water only
makes cleanup more difficult, messier, and time consuming.
9. The specific PAM copolymer formulation must be anionic. Cationic PAM shall not be used in any
application because of known aquatic toxicity concerns. Only the highest drinking water grade PAM,
certified for compliance with ANSI/NSF Standard 60 for drinking water treatment, may be used for
soil applications. The Washington State Department of Transportation (WSDOT) lists approved PAM
products on their web page. All PAM use shall be reviewed and approved by DLS-Permitting.
10. The PAM anionic charge density may vary from 2 – 30 percent; a value of 18 percent is typical.
Studies conducted by the United States Department of Agriculture (USDA)/ARS demonstrated that
soil stabilization was optimized by using very high molecular weight (12 – 15 mg/mole), highly
anionic (>20% hydrolysis) PAM.
11. PAM must be "water soluble" or "linear" or "non-cross-linked." Cross-linked or water absorbent
PAM, polymerized in highly acidic (pH<2) conditions, are used to maintain soil moisture content.
TABLE D.2.1.2.H PAM AND WATER APPLICATION RATES
Disturbed Area (ac) PAM (lbs) Water (gal)
0.50 0.25 500
1.00 0.50 1,000
1.50 0.75 1,500
2.00 1.00 2,000
2.50 1.25 2,500
3.00 1.50 3,000
3.50 1.75 3,500
4.00 2.00 4,000
4.50 2.25 4,500
5.00 2.50 5,000
Preferred Application Method
1. Pre-measure the area where PAM is to be applied and calculate the amount of product and water
necessary to provide coverage at the specified application rate (1/2 pound PAM/1,000 gallons/acre).
2. Dissolve pre-measured dry granular PAM with a known quantity of clean water in a bucket several
hours or overnight. PAM has infinite solubility in water, but dissolves very slowly. Mechanical
mixing will help dissolve PAM. Always add PAM to water – not water to PAM.
D.2.1.2 COVER MEASURES
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3. Pre-fill the water truck about 1/8 full with water. The water does not have to be potable, but it must
have relatively low turbidity – in the range of 20 NTU or less.
4. Add PAM/Water mixture to the truck.
5. Completely fill the water truck to specified volume.
6. Spray PAM/Water mixture onto dry soil until the soil surface is uniformly and completely wetted.
Alternate Application Method
PAM may also be applied as a powder at the rate of 5 pounds per acre. This must be applied on a day that
is dry. For areas less than 5-10 acres, a hand-held "organ grinder" fertilized spreader set to the smallest
setting will work. Tractor mounted spreaders will work for larger areas.
Maintenance Standards
1. PAM may be reapplied on actively worked areas after a 48-hour period
2. Reapplication is not required unless PAM treated soil is disturbed or unless turbidity levels show the
need for an additional application. If PAM treated soil is left undisturbed, a reapplication may be
necessary after two months. More PAM applications may be required for steep slopes, silty and clay
soils, (USDA classification Type "C" and "D" soils), long grades, and high precipitation areas. When
PAM is applied first to bare soil and then covered with straw, a reapplication may not be necessary for
several months.
D.2.1.2.9 COMPOST BLANKETS
Code: COBL Symbol:
Purpose
Compost blankets are intended to:
• Provide immediate temporary protection from erosion by protecting soil from rainfall and slowing
flow velocity over the soil surface.
• Enhance temporary or permanent plant establishment by conserving moisture, holding seed and
topsoil in place, providing nutrients and soil microorganisms, and moderating soil temperatures.
• Compost blankets, applied at the proper thickness and tilled into the soil, are also an option for
amending soils for permanent landscaping.
• Compost generally releases and adds phosphorous to stormwater. Therefore, compost blankets are not
recommended for use in watersheds where phosphorous sensitive water resources are located. Unless
prior approval is given by the County, they should not be used in Sensitive Lake Watersheds.
Conditions of Use
1. Compost blankets may be used unseeded on disturbed areas that require temporary cover measures up
to 1 year. Compost applied as temporary cover may be reclaimed and re-used for permanent cover.
2. Compost provides cover for protecting final grades until landscaping can be completed as it can be
directly seeded or tilled into soil as an amendment.
3. Compost blankets meet mulch requirements for seed.
4. Seed may be applied to a compost blanket at any time for permanent or temporary stabilization of
disturbed areas. Seed may be applied prior to blanket application, on top of blankets, or injected and
mixed into the compost as it is applied.
SECTION D.2.1 ESC MEASURES
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5. Compost blankets may be applied on slopes up to 2H:1V.
Design and Installation Specifications
1. Compost shall be applied at a minimum of 2 inches thick, unless otherwise directed by an ESC
supervisor or King County. At an application of 2 inches, this will equal approximately 100 tons per
acre (compost generally weighs approximately 800 lbs per cubic yard). Thickness shall be increased
at the direction of the design engineer for disturbed areas in or near critical areas or other areas highly
susceptible to erosion.
2. Compost shall meet criteria in Reference 11-C of the SWDM.
3. Compost shall be obtained from a supplier meeting the requirements in Reference 11-C.
4. Compost blankets shall be applied over the top of the slope to which it is applied, to prevent water
from running under the blanket
5. Compost blankets shall not be used in areas exposed to concentrated flow (e.g. channels, ditches,
dikes)
Maintenance Standards
1. The specified thickness of the blanket/cover must be maintained.
2. Any areas that show signs of erosion must be re-mulched. If the erosion problem is drainage related,
then the drainage problem must first be remedied and then the eroded area re-mulched.
D.2.1.3 PERIMETER PROTECTION
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D.2.1.3 PERIMETER PROTECTION
Perimeter protection to filter sediment from sheetwash shall be located downslope of all disturbed areas
and shall be installed prior to upslope grading. Perimeter protection includes the use of vegetated strips as
well as, constructed measures, such as silt fences, fiber rolls, sand/gravel barriers, brush or rock filters,
triangular silt dikes and other methods. During the wet season, 50 linear feet of silt fence (and the
necessary stakes) per acre of disturbed area must be stockpiled on site.
Purpose: The purpose of perimeter protection is to reduce the amount of sediment transported beyond the
disturbed areas of the construction site. Perimeter protection is primarily a backup means of sediment
control. Most, if not all, sediment-laden water is to be treated in a sediment trap or pond. The only
circumstances in which perimeter control is to be used as a primary means of sediment removal is when
the catchment is very small (see below).
When to Install: Perimeter protection is to be installed prior to any upslope clearing and grading.
Measures to Use: The above measures may be used interchangeably and are not the only perimeter
protection measures available. If surface water is collected by an interceptor dike or swale and routed to a
sediment pond or trap, there may be no need for the perimeter protection measures specified in this
section.
Criteria for Use as Primary Treatment: At the boundary of a site, perimeter protection may be used as
the sole form of treatment when the flowpath meets the criteria listed below. If these criteria are not met,
perimeter protection shall only be used as a backup to a sediment trap or pond.
Average Slope Slope Percent Flowpath Length
1.5H:1V or less 67% or less 100 feet
2H:1V or less 50% or less 115 feet
4H:1V or less 25% or less 150 feet
6H:1V or less 16.7% or less 200 feet
10H:1V or less 10% or less 250 feet
D.2.1.3.1 SILT FENCE
Code: SF Symbol:
Purpose
Use of a 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
1. Silt fence may be used downslope of all disturbed areas.
2. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of
overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment
trap or pond. The only circumstance in which overland flow may be treated solely by a silt fence,
rather than by a sediment trap or pond, is when the area draining to the fence is small (see "Criteria
for Use as Primary Treatment" in Section D.2.1.3 above).
Design and Installation Specifications
1. See Figure D.2.1.3.A and Figure D.2.1.3.B for details.
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2. The geotextile used must meet the standards listed below. A copy of the manufacturer's fabric
specifications must be available on site.
AOS (ASTM D4751) 30-100 sieve size (0.60-0.15 mm) for slit film
50-100 sieve size (0.30-0.15 mm) for other fabrics
Water Permittivity (ASTM D4491) 0.02 sec-1 minimum
Grab Tensile Strength (ASTM D4632)
(see Specification Note 3)
180 lbs. min. for extra strength fabric
100 lbs. min. for standard strength fabric
Grab Tensile Elongation (ASTM D4632) 30% max. (woven)
Ultraviolet Resistance (ASTM D4355) 70% min.
3. Standard strength fabric requires wire backing to increase the strength of the fence. Wire backing or
closer post spacing may be required for extra strength fabric if field performance warrants a stronger
fence.
4. Where the fence is installed, the slope shall be no steeper than 2H:1V.
5. If a typical silt fence (per Figure D.2.1.3.A) is used, the standard 4 x 4 trench may be reduced as long
as the bottom 8 inches of the silt fence is well buried and secured in a trench that stabilizes the fence
and does not allow water to bypass or undermine the silt fence.
Maintenance Standards
1. Any damage shall be repaired immediately.
2. If concentrated flows are evident uphill of the fence, they must be intercepted and conveyed to a
sediment trap or pond.
3. It is important to check the uphill side of the 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 or remove the trapped sediment.
4. Sediment must be removed when the sediment is 6 inches high.
5. If the filter fabric (geotextile) has deteriorated due to ultraviolet breakdown, it shall be replaced.
FIGURE D.2.1.3.A SILT FENCE
2"X2" BY 14 Ga. WIRE OR
EQUIVALENT, IF STANDARD
STRENGTH FABRIC USED
NOTE: FILTER FABRIC FENCES
SHALL BE INSTALLED ALONG
CONTOURS WHENEVER POSSIBLE
JOINTS IN FILTER FABRIC SHALL BE SPLICED
AT POSTS. USE STAPLES, WIRE RINGS OR
EQUIVALENT TO ATTACH FABRIC TO POSTS.
FILTER FABRIC
BACKFILL TRENCH WITH NATIVE SOIL
OR 3/4" TO 1-1/2" WASHED GRAVEL
MINIMUM 4"x4" TRENCH
2"x4" WOOD POSTS, STEEL FENCE
POSTS, REBAR, OR EQUIVALENT
POST SPACING MAY BE
INCREASED TO 8' IF
WIRE BACKING IS USED
6' MAX.2' MIN.12" MIN.
D.2.1.3 PERIMETER PROTECTION
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FIGURE D.2.1.3.B SILT FENCE INSTALLATION BY SLICING
1.GATHER FABRIC AT POSTS, IF NEEDED.
2.UTILIZE THREE TIES PER POST, ALL
WITHIN TOP 8" OF FABRIC.
3.POSITION EACH TIE DIAGONALLY,
PUNCTURING HOLES VERTICALLY A
MINIMUM OF 1" APART.
4.HANG EACH TIE ON A POST NIPPLE AND
TIGHTEN SECURELY. USE CABLE TIES
(50 LBS) OF SOFT WIRE.
TOP OF FABRIC
BELT
DIAGONAL ATTACHMENT
DOUBLES STRENGTH
FLOW
STEEL SUPPORT POST1.POST SPACING: 7' MAX. ON OPEN RUNS
4' MAX. ON POOLING AREAS.
2.POST DEPTH: AS MUCH BELOW GROUND
AS FABRIC ABOVE GROUND.
3.PONDING HEIGHT MAX. 24" ATTACH
FABRIC TO UPSTREAM SIDE OF POST.
4.DRIVE OVER EACH SIDE OF SILT FENCE
2 TO 4 TIMES WITH DEVICE EXERTING
60 P.S.I. OR GREATER.
5.NO MORE THAN 24" OF A 36" FABRIC
IS ALLOWED ABOVE GROUND.
6.VIBRATORY PLOW IS NOT ACCEPTABLE
BECAUSE OF HORIZONTAL COMPACTION.
100% COMPACTION
EACH SIDE
OPERATION
ROLL OF SILT FENCE
PLOW
FABRIC ABOVE
GROUND
HORIZONTAL CHISEL POINT
(76 mm WIDTH)200-300mm
SILT FENCE
TOP 8"
NOTES:
ATTACHMENT DETAILS:
SILT FENCE INSTALLATION BY SLICING METHOD
NTS
SECTION D.2.1 ESC MEASURES
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D.2.1.3.2 BRUSH BARRIER
Code: BB Symbol:
Purpose
The purpose of brush barriers is to reduce 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
1. Brush barriers may be used downslope of all disturbed areas.
2. Brush barriers are not intended to treat concentrated flows, nor are they intended to treat substantial
amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to
a sediment trap or pond. The only circumstance in which overland flow may be treated solely by a
barrier, rather than by a sediment trap or pond, is when the area draining to the barrier is small (see
"Criteria for Use as Primary Treatment" on page D-33).
Design and Installation Specifications
1. See Figure D.2.1.3.C for details.
2. King County may require filter fabric (geotextile) anchored over the brush berm to enhance the
filtration ability of the barrier.
Maintenance Standards
1. There shall be no signs of erosion or concentrated runoff under or around the barrier. If concentrated
flows are bypassing the barrier, it must be expanded or augmented by toed-in filter fabric.
2. The dimensions of the barrier must be maintained.
FIGURE D.2.1.3.C BRUSH BARRIER
IF REQUIRED, DRAPE FILTER FABRIC
OVER BRUSH AND SECURE IN 4"x4"
MIN. TRENCH WITH COMPACTED
BACKFILL
MAX. 6" DIAMETER WOODY DEBRIS
FOR BARRIER CORE. ALTERNATIVELY
TOPSOIL STRIPPINGS MAY BE USED
TO FORM THE BARRIER.
ANCHOR DOWNHILL EDGE OF
FILTER FABRIC WITH STAKES,
SANDBAGS, OR EQUIVALENT
2' MIN. HEIGHT
5' MIN.
D.2.1.3 PERIMETER PROTECTION
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D.2.1.3.3 VEGETATED STRIP
Code: VS Symbol:
Purpose
Vegetated strips reduce 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
1. Vegetated strips may be used downslope of all disturbed areas.
2. Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial
amounts of overland flow. Any concentrated flows must be conveyed through the draina ge system to
a sediment trap or pond. The only circumstance in which overland flow may be treated solely by a
strip, rather than by a sediment trap or pond, is when the area draining to the strip is small (see
"Criteria for Use as Primary Treatment" on page D-33).
Design and Installation Specifications
1. The vegetated strip shall consist of a 25-foot minimum width continuous strip of dense vegetation
with a permeable topsoil. Grass-covered, landscaped areas are generally not adequate because the
volume of sediment overwhelms the grass. Ideally, vegetated strips shall consist of undisturbed native
growth with a well-developed soil that allows for infiltration of runoff.
2. The slope within the strip shall not exceed 4H:1V.
3. The uphill boundary of the vegetated strip shall be delineated with clearing limits as specified in
Section D.2.1.1 (p. D-11).
Maintenance Standards
1. Any areas damaged by erosion or construction activity shall be seeded immediately and protected by
mulch.
2. If more than 5 feet of the original vegetated strip width has had vegetation removed or is being eroded,
sod must be installed using the standards for installation found in Section D.2.1.2.7.
If there are indications that concentrated flows are traveling across the buffer, surface water controls must
be installed to reduce the flows entering the buffer, or additional perimeter protection must be installed.
D.2.1.3.4 TRIANGULAR SILT DIKE (GEOTEXTILE ENCASED CHECK DAM)
Code: TSD Symbol:
Purpose
Triangular silt dikes (TSDs) may be used as check dams, for perimeter protection, for temporary soil
stockpile protection, for drop inlet protection, or as a temporary interceptor dike. Silt dikes, if attached to
impervious surfaces with tack or other adhesive agent may also be used as temporary wheel wash areas, or
concrete washout collection areas.
SECTION D.2.1 ESC MEASURES
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Conditions of Use
1. May be used for temporary check dams in ditches.
2. May be used on soil or pavement with adhesive or staples.
3. TSDs have been used to build temporary sediment ponds, diversion ditches, concrete washout
facilities, curbing, water bars, level spreaders, and berms.
Design and Installation Specifications
1. TSDs must be made of urethane foam sewn into a woven geosynthetic fabric.
2. TSDs are triangular, 10 inches to 14 inches high in the center, with a 20-inch to 28-inch base. A 2-
foot apron extends beyond both sides of the triangle along its standard section of 7 feet. A sleeve at
one end allows attachment of additional sections as needed
3. Install TSDs with ends curved up to prevent water from flowing around the ends
4. Attach the TSDs and their fabric flaps to the ground with wire staples. Wire staples must be No. 11
gauge wire or stronger and shall be 200 mm to 300 mm in length.
5. When multiple units are installed, the sleeve of fabric at the end of the unit shall overlap the abutting
unit and be stapled.
6. TSDs must be located and installed as soon as construction will allow.
7. TSDs must be placed perpendicular to the flow of water.
8. When used as check dams, the leading edge must be secured with rocks, sandbags, or a small key slot
and staples.
9. When used in grass-lined ditches and swales, the TSD check dams and accumulated sediment shall be
removed when the grass has matured sufficiently to protect the ditch or swale unless the slope of the
swale is greater than 4 percent. The area beneath the TSD check dams shall be seeded and mulched
immediately after dam removal.
Maintenance Standards
1. Triangular silt dikes shall be monitored for performance and sediment accumulation during and after
each runoff producing rainfall event. Sediment shall be removed when it reaches one half the height
of the silt dike.
2. Anticipate submergence and deposition above the triangular silt dike and erosion from high flows
around the edges of the dike/dam. Immediately repair any damage or any undercutting of the
dike/dam.
D.2.1.3.5 COMPOST BERMS
Code: COBE Symbol:
Purpose
Compost berms are an option to meet the requirements of perimeter protection. Compost berms may
reduce the transport of sediment from a construction site by providing a temporary physical barrier to
sediment and reducing the runoff velocities of overland flow. Compost berms trap sediment by filtering
water passing through the berm and allowing water to pond, creating a settling area for solids behind the
berm. Organic materials in the compost can also reduce concentrations of metals and petroleum
hydrocarbons from construction runoff. Due to the increase in phosphorous seen in the effluent data from
compost berms, they should be used with some cautions in areas that drain to phosphorus sensitive water
D.2.1.3 PERIMETER PROTECTION
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bodies, and should only be used in Sensitive Lake watersheds, such as Lake Sammamish, with the
approval from the County or the local jurisdiction.
Conditions of Use
1. Compost berms may be used in most areas requiring sediment or erosion control where runoff is in the
form of sheet flow or in areas where silt fence is normally considered acceptable. Compost berms
may be used in areas where migration of aquatic life such as turtles and salamanders are impeded by
the use of silt fence.
2. Compost berms are not intended to treat concentrated flows, nor are they intended to treat substantial
amounts of overland flow. Any concentrated flows must be conveyed via a drainage system to a
sediment pond or trap.
3. For purposes of long-term sediment control objectives, berms may be seeded at the time of installation
to create an additional vegetated filtering component.
Design and Installation Specifications
1. Compost berms shall be applied using a pneumatic blower device or equivalent, to produce a uniform
cross-section and berm density.
2. Compost berms shall be triangular in cross-section. The ratio of base to height dimensions shall be
2:1.
3. The minimum size of a compost berm is a 2-foot base with a 1-foot height.
4. Compost berms shall be sized and spaced as indicated in the table below.
SLOPE SLOPE Maximum Slope Length or
Berm Spacing (linear feet)
Berm Size Required
(height x base width)
0% - 2% Flatter than 50:1 250 1 ft x 2 ft
2% - 10% 50:1 – 10:1 125 1 ft x 2 ft
10% - 20% 10:1 – 5:1 100 1 ft x 2 ft
20% - 33% 5:1 – 3:1 75 1 ft x 2 ft
33% - 50% 3:1 – 2:1 50 1.5 ft x 3 ft
5. Compost berms shall not be used on slopes greater than 2H:1V.
6. Compost shall meet criteria in Reference 11-C of the SWDM except for the particle size distribution
(see Bullet 8).
7. Compost shall be obtained from a supplier meeting the requirements in Reference 11-C.
8. Compost particle size distribution shall be as follows: 99% passing a 1 inch sieve, 90% passing a ¾
inch sieve and a minimum of 70% greater than the 3/8 inch sieve. A total of 98% shall not exceed 3
inches in length.
9. Berms shall be placed on level contours to assist in dissipating flow into sheet flow rather than
concentrated flows. Berms shall not be constructed to concentrate runoff or channel water. Sheet flow
of water shall be perpendicular to the berm at impact. No concentrated flow shall be directed towards
compost berms.
10. Where possible, berms shall be placed 5 feet or more from the toe of slopes to allow space for
sediment deposition and collection.
11. In order to prevent water from flowing around the ends of the berms, the ends of the berm shall be
constructed pointing upslope so the ends are at a higher elevation than the rest of the berm.
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12. A compost blanket extending 10 – 15 feet above the berm is recommended where the surface above
the berm is rutted or uneven, to reduce concentrated flow and promote sheet flow into the berm.
Maintenance Standards
1. Compost berms shall be regularly inspected to make sure they retain their shape and allow adequate
flow-through of stormwater.
2. When construction is completed on site, the berms shall be dispersed for incorporation into the soil or
left on top of the site for final seeding to occur.
3. Any damage to berms must be repaired immediately. Damage includes flattening, compacting, rills,
eroded areas due to overtopping.
4. If concentrated flows are evident uphill of the berm, the flows must be intercepted and conveyed to a
sediment trap or pond.
5. The uphill side of the berm shall be inspected for signs of the berm clogging and acting as a barrier to
flows and causing channelization of flows parallel to the berm. If this occurs, replace the berm or
remove the trapped sediment.
6. Sediment that collects behind the berm must be removed when the sediment is more than 6 inches
deep.
D.2.1.3.6 COMPOST SOCKS
Code: COSO Symbol:
Purpose
Compost socks reduce the transport of sediment from a construction site by providing a temporary
physical barrier to sediment-laden water and reducing the runoff velocities of overland flow. Compost
socks trap sediment by filtering water that passes through the sock and allows water to pond behind the
sock, creating a settling area for solids. Organic materials in the compost also may reduce metal and
petroleum hydrocarbon concentrations in construction runoff. Compost socks function similarly to
compost berms; however, because the compost is contained in a mesh tube, they are appropriate for both
concentrated flow and sheet flow. Compost socks may be used to channel concentrated flow on hard
surfaces.
Conditions of Use
1. Compost socks may be used in areas requiring sediment or erosion control where runoff is in the form
of sheet flow or in areas that silt fence is normally considered acceptable. Compost socks may also be
used in sensitive environmental areas where migration of aquatic life, including turtles, salamanders
and other aquatic life may be impeded by the used of silt fence.
2. Compost socks are not intended to treat substantial amounts of overland flow. However, compost
socks may be subjected to some ponding and concentrated flows. If intended primarily as a filtration
device, the socks should be sized and placed so that flows do not overtop the socks.
3. For purposes of long term sediment control objectives, compost socks may be seeded at the time of
installation to create an additional vegetated filtering component.
Design and Installation Specifications
1. Compost socks shall be produced using a pneumatic blower hose or equivalent to fill a mesh tube with
compost to create a uniform cross-section and berm density.
D.2.1.4 TRAFFIC AREA STABILIZATION
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2. Socks shall be filled so they are firmly – packed yet flexible. Upon initial filling, the socks shall be
filled to have a round cross-section. Once placed on the ground, it is recommended to apply weight to
the sock to improve contact with the underlying surface. This may cause the sock to assume an oval
shape.
3. Compost socks shall be a minimum of 8 inches in diameter. Larger diameter socks are recommended
for areas where ponding is expected behind the sock.
4. Compost socks shall not be used on slopes greater than 2H:1V.
5. Compost shall meet criteria in Reference 11-C of the SWDM, except for the particle size distribution
(see Bullet 7).
6. Compost shall be obtained from a supplier meeting the requirements in Reference 11-C.
7. Compost particle size distribution shall be as follows: 99% passing a 1 inch sieve, 90% passing a ¾
inch sieve and a minimum of 70% greater than the 3/8 inch sieve. A total of 98% shall not exceed 3
inches in length.
8. In order to prevent water from flowing around the ends of compost socks, the ends must be pointed
upslope so the ends of the socks are at a higher elevation than the remainder of the sock.
Maintenance Standards
1. Compost socks shall be regularly inspected to make sure the mesh tube remains undamaged, the socks
retain their shape, and allow adequate flow through of surface water. If the mesh tube is torn, it shall
be repaired using twine, zip-ties, or wire. Large sections of damaged socks must be replaced. Any
damage must be repaired immediately upon discovery of damage.
2. When the sock is no longer needed, the socks shall be cut open and the compost dispersed to be
incorporated into the soil or left on top of the soil for final seeding to occur. The mesh material must
be disposed of properly as solid waste. If spills of oil, antifreeze, hydraulic fluid, or other equipment
fluids have occurred that have saturated the sock, the compost must be disposed of properly as a
waste.
3. Sediment must be removed when sediment accumulations are within 3 inches of the top of the sock.
D.2.1.4 TRAFFIC AREA STABILIZATION
Unsurfaced entrances, roads, and parking areas used by construction traffic shall be stabilized to minimize
erosion and tracking of sediment off site. Stabilized construction entrances shall be installed as the first
step in clearing and grading. At the County's discretion, road and parking area stabilization is not required
during the dry season (unless dust is a concern) or if the site is underlain by coarse-grained soils. Roads
and parking areas shall be stabilized immediately after initial grading.
Purpose: The purpose of traffic area stabilization is to reduce the amount of sediment transported off site
by construction vehicles and to reduce the erosion of areas disturbed by vehicle traffic. Sediment
transported off site onto paved streets is a significant problem because it is difficult to effectively remove,
and any sediment not removed ends up in the drainage system. Additionally, sediment on public right-of-
way can pose a serious traffic hazard. Construction road and parking area stabilization is important
because the combination of wet soil and heavy equipment traffic typically forms a slurry of easily erodible
mud. Finally, stabilization also is an excellent form of dust control in the summer months.
When to Install: The construction entrance is to be installed as the first step in clearing and grading.
Construction road stabilization shall occur immediately after initial grading of the construction roads and
parking areas.
Measures to Use: There are two types of traffic area stabilization: (1) a stabilized construction entrance
and (2) construction road/parking area stabilization. Both measures must be used as specified under
"Conditions of Use" for each measure.
SECTION D.2.1 ESC MEASURES
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D-42
D.2.1.4.1 STABILIZED CONSTRUCTION ENTRANCE
Code: CE Symbol:
Purpose
Construction entrances are stabilized to reduce the amount of sediment transported onto paved roads by
motor vehicles or runoff by constructing a stabilized pad of quarry spalls at entrances to construction sites.
Conditions of Use
Construction entrances shall be stabilized wherever traffic will be leaving a construction site and traveling
on paved roads or other paved areas within 1,000 feet of the site. Access and exits shall be limited to one
route if possible, or two for linear projects such as roadway where more than one access/exit is necessary
for maneuvering large equipment.
For residential construction provide stabilized construction entrances for each residence in addition to the
main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle
access/parking, based on lot size/configuration.
Design and Installation Specifications
1. See Figure D.2.1.4.A for details.
2. 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 following standards:
Grab Tensile Strength (ASTM D4632) 200 lbs min.
Grab Tensile Elongation (ASTM D4632) 30% max.(woven)
Puncture Strength (ASTM D6241) 495 lbs min.
AOS (ASTM D4751) 20-45 (U.S. standard sieve size)
3. Do not use crushed concrete, cement, or calcium chloride for construction entrance stabilization
because these products raise pH levels in stormwater and concrete discharge to surface waters of the
State is prohibited.
4. Hog fuel (wood based mulch) may be substituted for or combined with quarry spalls in areas that will
not be used for permanent roads. The effectiveness of hog fuel is highly variable, but it has been used
successfully on many sites. It generally requires more maintenance than quarry spalls. Hog fuel is not
recommended for entrance stabilization in urban areas. The inspector may at any time require the use
of quarry spalls if the hog fuel is not preventing sediment from being tracked onto pavement or if the
hog fuel is being carried onto pavement. Hog fuel is prohibited in permanent roadbeds because
organics in the subgrade soils cause difficulties with compaction.
5. Fencing (see Section D.2.1.1) shall be installed as necessary to restrict traffic to the construction
entrance.
6. Whenever possible, the entrance shall be constructed on a firm, compacted subgrade. This can
substantially increase the effectiveness of the pad and reduce the need for maintenance.
Maintenance Standards
1. Quarry spalls (or hog fuel) shall be added if the pad is no longer in accordance with the specifications.
D.2.1.4 TRAFFIC AREA STABILIZATION
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-43
2. If the entrance 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 street sweeping, an
increase in the dimensions of the entrance, or the installation of a wheel wash. If washing is used, it
shall be done on an area covered with crushed rock, and wash water shall drain to a sediment trap or
pond.
3. Any sediment that is tracked onto pavement shall be removed immediately by sweeping. 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 sweeping is ineffective and there is a threat to public
safety. If it is necessary to wash the streets, a small sump must be constructed. The sediment would
then be washed into the sump where it can be controlled. Wash water must be pumped back onto the
site and cannot discharge to systems tributary to surface waters.
4. Any quarry spalls that are loosened from the pad and end up on the roadway shall be removed
immediately.
5. If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing (see
Section D.2.1.1) shall be installed to control traffic.
FIGURE D.2.1.4.A STABILIZED CONSTRUCTION ENTRANCE
•PER KING COUNTY ROAD DESIGN AND CONSTRUCTION STANDARDS (KCRDCS), DRIVEWAYS SHALL
BE PAVED TO EDGE OF R-O-W PRIOR TO INSTALLATION OF THE CONSTRUCTION ENTRANCE TO
AVOID DAMAGING OF THE ROADWAY.
•IT IS RECOMMENDED THAT THE ENTRANCE BE CROWNED SO THAT RUNOFF DRAINS OFF THE PAD.
12" MIN.
THICKNESS
PROVIDE FULL WIDTH OF
INGRESS/EGRESS AREA
IF A ROADSIDE DITCH IS
PRESENT, INSTALL
DRIVEWAY CULVERT
PER KCRDCS
GEOTEXTILE
4"- 8" QUARRY
SPALLS
R=25' MIN.
100
'
M
I
N
.
EXISTI
N
G
R
O
A
D
15' MI
N.
NOTES:
SECTION D.2.1 ESC MEASURES
7/23/2021 2021 Surface Water Design Manual – Appendix D
D-44
D.2.1.4.2 CONSTRUCTION ROAD/PARKING AREA STABILIZATION
Code: CRS Symbol:
Purpose
Stabilizing subdivision roads, parking areas and other onsite vehicle transportation routes immediately
after grading reduces erosion caused by construction traffic or runoff.
Conditions of Use
1. Roads or parking areas shall be stabilized wherever they are constructed, whether permanent or
temporary, for use by construction traffic.
2. Fencing (see Section D.2.1.1) shall be installed, if necessary, to limit the access of vehicles to only
those roads and parking areas that are stabilized.
Design and Installation Specifications
1. A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed surfacing base course shall be
applied immediately after grading or utility installation. A 4-inch course of asphalt treated base
(ATB) may also be used, or the road/parking area may be paved. It may also be possible to use
cement or calcium chloride for soil stabilization. If the area will not be used for permanent roads,
parking areas, or structures, a 6-inch depth of hog fuel may also be used, but this is likely to require
more maintenance. Whenever possible, construction roads and parking areas shall be placed on a
firm, compacted subgrade. Note: If the area will be used for permanent road or parking installation
later in the project, the subgrade will be subject to inspection.
2. Temporary road gradients shall not exceed 15 percent. Roadways shall be carefully graded to drain
transversely. Drainage ditches shall be provided on each side of the roadway in the case of a crowned
section, or on one side in the case of a super-elevated section. Drainage ditches shall be designed in
accordance with the standards given in Section D.2.1.6.4 (p. D-64) and directed to a sediment pond or
trap.
3. Rather than relying on ditches, it may also be possible to grade the road so that runoff sheet-flows
into a heavily vegetated area with a well-developed topsoil. Landscaped areas are not adequate. If
this area has at least 50 feet of vegetation, then it is generally preferable to use the vegetation to treat
runoff, rather than a sediment pond or trap. The 50 feet shall not include vegetated wetlands. If
runoff is allowed to sheet flow through adjacent vegetated areas, it is vital to design the roadways and
parking areas so that no concentrated runoff is created.
4. In order to control construction traffic, the County may require that signs be erected on site informing
construction personnel that vehicles, other than those performing clearing and grading, are restricted
to stabilized areas.
5. If construction roads do not adequately reduce trackout to adjacent property or roadways, a wheel
wash system will be required.
Maintenance Standards
Crushed rock, gravel base, hog fuel, etc. shall be added as required to maintain a stable driving surface and
to stabilize any areas that have eroded.
D.2.1.4 TRAFFIC AREA STABILIZATION
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D-45
D.2.1.4.3 WHEEL WASH
Code: WW Symbol:
Purpose
Wheel wash systems reduce the amount of sediment transported onto paved roadways and into surface
water systems by construction vehicles.
Conditions of Use
When a stabilized construction entrance is not preventing sediment from being tracked onto pavement:
• Wheel washing is generally an effective erosion and sediment control method and BMP when
installed with careful attention to topography. For example, a wheel wash can be detrimental if
installed at the top of a slope abutting a right-of-way where the water from the dripping truck wheels
and undercarriage can run unimpeded into the street.
• Pressure washing combined with an adequately sized and properly surfaced wash pad with direct
drainage discharge to a large 10 foot x 10-foot sump can be very effective.
Design and Installation Specifications
A suggested detail is shown in Figure D.2.1.4.B.
1. A minimum of 6inches of asphalt treated base (ATB) over crushed base material or 8 inches over a
good subgrade is recommended to pave the wheel wash area.
2. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will
work well to test clearance.
3. Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck
tongues with water.
4. Midpoint spray nozzles are only needed in very muddy conditions.
5. Wheel wash systems should be designed with a small grade change, 6 to 12 inches for a 10-foot wide
pond, to allow sediment to flow to the low side of the pond and to help prevent re-suspension of
sediment.
6. A drainpipe with a 2 to 3 foot riser should be installed on the low side of the wheel wash pond to
allow for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation
in a closed-loop system.
7. Polyacrylamide (PAM) added to the wheel washwater at a rate of 0.25 – 0.5 pounds per 1,000 gallons
of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or
erosion control and is being applied by a water truck, the same truck may be used to change the
washwater.
Maintenance Standards
1. The wheel wash should start out each day with clean, fresh water.
2. The washwater should be changed a minimum of once per day. On large earthwork jobs where more
than 10-20 trucks per hour are expected, the washwater will need to be changed more often.
3. Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system that
prevents discharge to surface water, or to the sanitary sewer system with proper local sewer district
approval or permits.
SECTION D.2.1 ESC MEASURES
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D-46
FIGURE D.2.1.4.B WHEEL WASH AND PAVED CONSTRUCTION ENTRANCE
2%
SLOPE
15'15'20'15'50'
18'
12'
3'
5'
BUILD 8'x8' SUMP TO ACCOMODATE
CLEANING BY TRACKHOE.
SECTION A-A
NTS
8'x8' SUMP,
SEE NOTE
LOCATE INVERT OF TOP
PIPE 1' ABOVE BOTTOM
OF WHEEL WASH
DRAIN PIPE 1:1 SLOPE
WATER LEVEL
ELEVATION VIEW
NTS
PLAN VIEW
NTS
6" SLEEVE
CURB
ASPHALT CURB ON THE
LOW ROAD SIDE TO DIRECT
WATER BACK TO POND
6" ATB CONSTRUCTION
ENTRANCE
1-1/2" SCHEDULE 40
FOR SPRAYERS
2% SLOPE
MIDPOINT SPRAY
NOZZLES, IF NEEDED
3" TRASH PUMP WITH FLOATS
ON SUCTION HOSE
2" SCHEDULE 40
6" SLEEVE UNDER ROAD
8'x8' SUMP WITH 5'
OF CATCH
6" SEWER PIPE WITH
BUTTERFLY VALVES
1:1 SLOPE
A
A
5:1
SLOPE
5:1
SLOPE
15' ATB APRON TO PROTECT
GROUND FROM SPLASHING WATER
BALL VALVES
NOTE:
D.2.1.5 SEDIMENT RETENTION
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-53
FIGURE D.2.1.5.D SEDIMENT POND RISER DETAIL
3.5' MIN.
18" MIN.
2X RISER DIA. MIN.
CORRUGATED
METAL RISER
CONCRETE BASE ALTERNATIVELY, METAL
STAKES AND WIRE MAY
BE USED TO PREVENT
FLOTATION
DEWATERING ORIFICE,
SCHEDULE 40 STEEL
STUB MIN. DIAMETER
AS PER CALCULATIONS
6" MIN.
PROVIDE
ADEQUATE
STRAPPING
POLYETHYLENE CAP
PERFORATED
DEWATERING DEVICE,
SEE NOTE WATERTIGHT
COUPLING TACK
WELD
NOTE:
PERFORATED CORRUGATED
POLYETHYLENE (CPE)
DRAINAGE TUBING, DIAMETER
MIN. 2" LARGER THAN
DEWATERING ORIFICE. TUBING
SHALL COMPLY WITH ASTM
F667 AND AASHTO M294.
D.2.1.5.3 STORM DRAIN INLET PROTECTION
Code: FFP or CBI or CBP Symbol: or or
Purpose
Storm drain inlets are protected to prevent coarse sediment from entering storm drainage systems.
Temporary devices around storm drains assist in improving the quality of water discharged to inlets or
catch basins by ponding sediment-laden water. These devices are effective only for relatively small
drainage areas.
Conditions of Use
1. Protection shall be provided for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area, unless the runoff that enters the catch basin will be conveyed to a sediment pond or
trap.
2. Inlet protection may be used anywhere at the applicant's discretion to protect the drainage system.
This will, however, require more maintenance, and it is highly likely that the drainage system will still
require some cleaning.
3. The contributing drainage area must not be larger than one acre.
Design and Installation Specifications
1. There are many options for protecting storm drain inlets. Two commonly used options are filter
fabric protection and catch basin inserts. Filter fabric protection (see Figure D.2.1.5.E) is filter fabric
(geotextile) placed over the grate. This method is generally very ineffective and requires intense
maintenance efforts. Catch basin inserts (see Figure D.2.1.5.F) are manufactured devices that nest
inside a catch basin. This method also requires a high frequency of maintenance to be effective. Both
SECTION D.2.1 ESC MEASURES
7/23/2021 2021 Surface Water Design Manual – Appendix D
D-54
options provide adequate protection, but filter fabric is likely to result in ponding of water above the
catch basin, while the insert will not. Thus, filter fabric is only allowed where ponding will not be a
traffic concern and where slope erosion will not result if the curb is overtopped by ponded water.
Trapping sediment in the catch basins is unlikely to improve the water quality of runoff if it is treated
in a pond or trap because the coarse particles that are trapped at the catch basin settle out very quickly
in the pond or trap. Catch basin protection normally only improves water quality where there is
no treatment facility downstream. In these circumstances, catch basin protection is an important
last line of defense. It is not, however, a substitute for preventing erosion.
The placement of filter fabric under grates is generally prohibited and the use of filter fabric over
grates is strictly limited and discouraged.
2. It is sometimes possible to construct a small sump around the catch basin before final surfacing of the
road. This is allowed because it can be a very effective method of sediment control.
3. Block and gravel filters, gravel and wire mesh filter barriers, and bag barriers filled with various
filtering media placed around catch basins can be effective when the drainage area is 1 acre or less and
flows do not exceed 0.5 cfs. It is necessary to allow for overtopping to prevent flooding. Many
manufacturers have various inlet protection filters that are very effective in keeping sediment-laden
water from entering the storm drainage system. The following are examples of a few common
methods.
a) Block and gravel filters (Figure D.2.1.5.G) are a barrier formed around an inlet with standard
concrete block and gravel, installed as follows:
• Height is 1 to 2 feet above the inlet.
• Recess the first row of blocks 2 inches into the ground for stability.
• Support subsequent rows by placing a 2x4 through the concrete block opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the pooled water.
• Place cloth or mesh with ½ inch openings over all block openings.
• Place gravel below the top of blocks on slopes of 2:1 or flatter.
• An alternate design is a gravel donut.
b) Gravel and wire mesh filters consist of a gravel barrier placed over the top of an inlet. This
structure generally does not provide overflow. Install as follows:
• Cloth or comparable wire mesh with ½ inch openings is placed over inlet.
• Coarse aggregate covers the cloth or mesh.
• Height/depth of gravel should be 1 foot or more, 18 inches wider than inlet on all sides.
c) Curb inlet protection with a wooden weir is a barrier formed around an inlet with a wooden
frame and gravel, installed as follows:
• Construct a frame and attach wire mesh (½ inch openings) and filter fabric to the frame.
• Pile coarse washed aggregate against the wire/fabric.
• Place weight on frame anchors.
d) Curb and gutter sediment barriers (Figure D.2.1.5.H) consist of sandbags or rock berms (riprap
and aggregate) 3 feet high and 3 feet wide in a horseshoe shape, installed as follows:
• Bags of either burlap or woven geotextile fabric, filled with a variety of media such as gravel,
wood chips, compost or sand stacked tightly allows water to pond and allows sediment to
separate from runoff.
D.2.1.5 SEDIMENT RETENTION
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-55
• Leave a "one bag gap" in the top row of the barrier to provide a spillway for overflow.
• Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 x 3 and at
least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the outside of the berm to sediment trap
standards for protecting a culvert inlet.
4. Excavated drop inlet sediment traps are appropriate where relatively heavy flows are expected and
overflow capability is needed. If emergency overflow is provided, additional end-of-pipe treatment
may be required. Excavated drop inlets consist of an excavated impoundment area around a storm
drain. Sediment settles out of the stormwater prior to enter the drain. Install according to the following
specifications:
a) The impoundment area should have a depth of 1 - 2 feet measured from the crest of the inlet
structure.
b) Side slopes of the excavated area must be no steeper than 2:1.
c) Minimum volume of the excavated area should be 35 cubic yards.
d) Install provisions for draining the area to prevent standing water problems.
e) Keep the area clear of debris.
f) Weep holes may be drilled into the side of the inlet.
g) Protect weep holes with wire mesh and washed aggregate.
h) Weep holes must be sealed when removing and stabilizing excavated area.
i) A temporary dike may be necessary on the down slope side of the structure to prevent bypass
flow.
Maintenance Standards
1. Any accumulated sediment on or around inlet protection shall be removed immediately. Sediment
shall not be removed with water, and all sediment must be disposed of as fill on site or hauled off site.
2. Any sediment in the catch basin insert shall be removed when the sediment has filled one-third of the
available storage. The filter media for the insert shall be cleaned or replaced at least monthly.
3. Regular maintenance is critical for all forms of catch basin/inlet protection. Unlike many forms of
protection that fail gradually, catch basin protection will fail suddenly and completely if not maintained
properly.
SECTION D.2.1 ESC MEASURES
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D-56
FIGURE D.2.1.5.E FILTER FABRIC PROTECTION
FIGURE D.2.1.5.F CATCH BASIN INSERT
CATCH BASIN
NOTE: ONLY TO BE USED WHERE
PONDING OF WATER ABOVE THE
CATCH BASIN WILL NOT CAUSE
TRAFFIC PROBLEMS AND WHERE
OVERFLOW WILL NOT RESULT IN
EROSION OF SLOPES.
GRATE
STANDARD STRENGTH
FILTER FABRIC
NOTE: THIS DETAIL IS ONLY
SCHEMATIC. ANY INSERT IS
ALLOWED THAT HAS:
•A MIN. 0.5 C.F. OF STORAGE,
•THE MEANS TO DEWATER THE
STORED SEDIMENT,
•AN OVERFLOW, AND
•CAN BE EASILY MAINTAINED.
OVERFLOW
GRATECATCH BASIN
POROUS
BOTTOM
SOLID
WALLS
FILTER
MEDIA FOR
DEWATERING
D.2.1.5 SEDIMENT RETENTION
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-57
FIGURE D.2.1.5.G BLOCK AND GRAVEL CURB INLET PROTECTION
1.USE BLOCK AND GRAVEL TYPE SEDIMENT BARRIER WHEN CURB INLET IS LOCATED
IN GENTLY SLOPING 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 STORM EVENT. SEDIMENT
AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY.
2x4 WOOD STUD
OVERFLOW
WATER
A
A
PLAN VIEW
NTS
SECTION A-A
NTS
BLOCK AND GRAVEL CURB INLET PROTECTION
NTS
CATCH BASIN COVER
CURB INLET
CONCRETE BLOCKS
CATCH BASIN COVER
CURB INLET
CATCH BASIN
BACK OF SIDEWALK
CURB FACE
3/4" DRAIN
GRAVEL (20 mm)
WIRE SCREEN OR
FILTER FABRIC
POND HEIGHT
WIRE SCREEN
OR FILTER FABRIC
2x4 WOOD STUD
(100x50 TIMBER STUD)
3/4" DRAIN
GRAVEL (20 mm)
NOTES:
SECTION D.2.1 ESC MEASURES
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D-58
FIGURE D.2.1.5.H CURB AND GUTTER BARRIER PROTECTION
RUNOFF
RUNOFF
SPILLWAY
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.
GRAVEL FILLED SANDBAGS
STACKED TIGHTLY
DRAIN GRATE
GUTTER
CURB FACE
CURB INLET
SANDBAGS TO OVERLAP
ONTO CURB
BACK OF SIDEWALK
PLAN VIEW
NTS
CURB AND GUTTER BARRIER
NTS
NOTES:
SECTION D.2.1 ESC MEASURES
7/23/2021 2021 Surface Water Design Manual – Appendix D
D-64
Design and Installation Specifications
1. Two types of drains may be used as follows:
a) Relief drains are used either to lower the water table in large, relatively flat areas, improve the
growth of vegetation, or to remove surface water. They are installed along a slope and drain in
the direction of the slope. They may be installed in a grid pattern, a herringbone pattern, or a
random pattern.
b) Interceptor drains are used to remove excess groundwater from a slope, stabilize steep slopes,
and lower the water table below a slope to prevent the soil from becoming saturated. They are
installed perpendicular to a slope and drain to the side of the slope. They usually consist of a
single pipe or single pipes instead of a patterned layout.
2. Size of Drains – Size subsurface drains to carry the required capacity without pressurized flow.
Minimum diameter for a subsurface drain is 4 inches.
3. Outlet – Ensure that the outlet of a drain empties into a channel or other watercourse above the
normal water level.
Maintenance Standards
1. Subsurface drains shall be checked periodically to ensure that they are free flowing and not clogged
with sediment or roots.
2. The outlet shall be kept clear and free of debris.
3. Surface inlets shall be kept open and free of sediment and other debris.
4. Trees located too close to a subsurface drain often clog the system with roots. If a drain becomes
clogged, relocate the drain or remove the trees as a last resort. Drain placement should be planned to
minimize this problem.
5. Where drains are crossed by heavy equipment, the line shall be checked to ensure that it is not crushed
and have adequate cover protection.
D.2.1.6.4 DITCHES
Code: DI Symbol:
Purpose
Ditches convey intercepted runoff from disturbed areas to and from sediment ponds or traps. They also
convey runoff intercepted from undisturbed areas around the site to a non-erosive discharge point.
Conditions of Use
Ditches may be used anywhere that concentrated runoff is to be conveyed on or around the construction
site. Temporary pipe systems may also be used to convey runoff.
Design and Installation Specifications
1. Channels and ditches shall be sized to accommodate the developed condition 10-year approved model
15-minute peak flow with 0.5 feet of freeboard. If no hydrologic analysis is required for the site, the
Rational Method may be used [see Section 3.2.1 of the King County Surface Water Design Manual
(SWDM)].
2. See SWDM Section 4.4.1 for open-channel design requirements.
D.2.1.6 SURFACE WATER COLLECTION
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-65
3. The only exception to the requirements of SWDM Section 4.4.1 is the use of check dams, rather than
grass lining, for channels in which the design flow velocity does not exceed 5 fps. See Figure
D.2.1.6.E for details on check dam installation.
Maintenance Standards
1. Any sediment deposition of more than 0.5 feet shall be removed so that the channel is restored to its
design capacity.
2. If the channel capacity is insufficient for the design flow, it must be determined whether the problem
is local (e.g., a constriction or bend) or the channel is under-designed. If the problem is local, the
channel capacity must be increased through construction of a berm(s) or by excavation. If the
problem is under-design, the design engineer shall be notified and the channel redesigned to a more
conservative standard to be approved by King County.
3. The channel shall be examined for signs of scouring and erosion of the bed and banks. If scouring or
erosion has occurred, affected areas shall be protected by riprap or an erosion control blanket or net.
FIGURE D.2.1.6.E CHECK DAMS
6" MIN.
ROCK MUST COMPLETELY COVER
THE BOTTOM AND SIDES OF THE DITCH
24" MIN.
2H:1V SLOPES
L 2"- 4" ROCKBA
L=THE DISTANCE SUCH THAT POINTS
A AND B ARE OF EQUAL ELEVATION
CROSS SECTION
CHECK DAM SPACING
D.2.1.6 SURFACE WATER COLLECTION
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D-69
D.2.1.7 DEWATERING CONTROL
Any runoff generated by dewatering shall be treated through construction of a sediment trap (Section
D.2.1.5.1) when there is sufficient space or by releasing the water to a well vegetated, gently sloping area.
Since pumps are used for dewatering, it may be possible to pump the sediment-laden water well away
from the surface water so that vegetation can be more effectively utilized for treatment. Discharge of
sediment-laden water from dewatering activities to surface and storm waters is prohibited. If dewatering
occurs from areas where the water has come in contact with new concrete, such as tanks, vaults, or
foundations, the pH of the water must be monitored and must be neutralized prior to discharge. Clean
non-turbid dewatering water, such as well point ground water can be discharged to systems tributary to, or
directly to surface waters provided the flows are controlled so no erosion or flooding occurs. Clean water
must not be routed through a stormwater sediment pond. Highly turbid or contaminated dewatering water
must be handled separately from stormwater.
Purpose: To prevent the untreated discharge of sediment-laden water from dewatering of utilities,
excavated areas, foundations, etc.
When to Install: Dewatering control measures shall be used whenever there is a potential for runoff from
dewatering of utilities, excavations, foundations, etc.
Measures to install:
1. Foundation, vault, excavation, and trench dewatering water that has similar characteristics to
stormwater runoff at the site shall be discharged into a controlled conveyance system prior to
discharge to a sediment trap or sediment pond. Foundation and trench dewatering water that has
similar characteristics to stormwater runoff at the site must be disposed of through one of the
following options depending on site constraints:
a) Infiltration,
b) Transport offsite in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that
does not pollute surface waters,
c) Discharge to the sanitary sewer discharge with local sewer district approval if there is no other
option, or
d) Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized
dewatering.
2. Clean, non-turbid dewatering water, such as well-point ground water, may be discharged via stable
conveyance to systems tributary to surface waters, provided the dewatering flow does not cause
erosion or flooding of receiving waters.
3. Highly turbid or contaminated dewatering water (high pH or other) shall be handled separately
from stormwater. See Section D.2.2 (p. D-76), SWPPS Measures.
SECTION D.2.1 ESC MEASURES
7/23/2021 2021 Surface Water Design Manual – Appendix D
D-70
D.2.1.8 DUST CONTROL
Preventative measures to minimize the wind transport of soil shall be taken when a traffic hazard may be
created or when sediment transported by wind is likely to be deposited in water resources or adjacent
properties.
Purpose: To prevent wind transport of dust from exposed soil surfaces onto roadways, drainage ways, and
surface waters.
When to Install: Dust control shall be implemented when exposed soils are dry to the point that wind
transport is possible and roadways, drainage ways, or surface waters are likely to be impacted. Dust
control measures may consist of chemical, structural, or mechanical methods.
Measures to Install: Water is the most common dust control (or palliative) used in the area. When using
water for dust control, the exposed soils shall be sprayed until wet, but runoff shall not be generated by
spraying. Calcium chloride, Magnesium chloride, Lignin derivatives, Tree Resin Emulsions, and
Synthetic Polymer Emulsions may also be used for dust control. Exposed areas shall be re-sprayed as
needed. Oil shall not be used for dust control. The following table lists many common dust control
measures. Some of the measures are not recommended for use in King County and must have prior
approval prior to use from the DLS-Permitting inspector assigned to specific projects.
D.2.1.8 DUST CONTROL
2021 Surface Water Design Manual – Appendix D 7/23/2021
D-71
TABLE D.2.1.8.A DUST CONTROL MEASURES
METHOD CONSIDERATIONS SITE PREPARATION RECOMMENDED
APPLICATION RATE
Water -Most commonly used practice
-Evaporates quickly
-Lasts less than 1 day
For all liquid agents:
-Blade a small surface
-Crown or slope surface to avoid
ponding
-Compact soils if needed
-Uniformly pre-wet at
0.03 – 0.3 gal/sq yd
-Apply solution under pressure.
Overlap solution 6 – 12 inches
-Allow treated area to cure
0 – 4 hours
-Compact area after curing
-Apply second treatment before first
treatment becomes ineffective
0.125 gal/sq yd every
20 to 30 minutes
Salts
Calcium
Chloride
(CaCl)
-Restricts evaporation
-Lasts 6-12 months
-Can be corrosive
-Less effective in low humidity
-Can build up in soils and leach by rain
Apply 38% solution at
1.21L/m2 (0.27 gal/yd2)
or as loose dry granules
per manufacturer
Magnesium
Chloride
(MgCl)
-Restricts evaporation
-Works at higher temperatures and lower
humidity than CaCl
-May be more costly than CaCl
Apply 26 – 32% solution
at 2.3 L/m2 (0.5
gal/yd2)
Sodium
Chloride
(NaCl)
-Effective over smaller range of
conditions
-Less expensive
-Can be corrosive
-Less effective in low humidity
Per Manufacturer
Silicates -Generally expensive
-Available in small quantities
-Require Second application
Surfactants -High evaporation rates
-Effective for short time periods
-Must apply frequently
Copolymers -Forms semi-permeable transparent
crust
-Resists ultraviolet radiation and
moisture induced breakdown
-Last 1 to 2 years
750 – 940 L/ha (80 –
100 gal/ac)
Petroleum
Products
-Used oil is prohibited as a dust control
method
-Bind soil particles
-May hinder foliage growth
-Environmental and aesthetic concerns
-Higher cost
Use 57 – 63% resins as
base. Apply at 750 –
940 L/ha (80-100
gal/ac)
Lignin
Sulfonate
-Paper industry waste product
-Acts as dispersing agent
-Best in dry climates
-Can be slippery
-Will decrease Dissolved Oxygen in
waterways therefore cannot be used
adjacent to surface water systems
Loosen surface 25-50
mm (1 – 2 inches) Need
4-8% fines
Vegetable
Oils
-Coat grains of soils, so limited binding
ability
-May become brittle
-Limited availability
Per Manufacturer
Spray on
Adhesives
-Available as organic or synthetic
-Effective on dry, hard soils
-Forms a crust
-Can last 3 to 4 years
Per Manufacturer
Appendix D:
Site Inspection
Form
Construction Stormwater Site Inspection Form
Page 1
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 Construction/installation of erosion/sediment controls 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 cm pH
Turbidity tube, meter, laboratory
pH Paper, kit, meter
Construction Stormwater Site Inspection Form
Page 2
D. Check the observed status of all items. Provide “Action Required “details and dates.
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
1
Clearing
Limits
Before beginning land disturbing
activities are all clearing limits,
natural resource areas (streams,
wetlands, buffers, trees) protected
with barriers or similar BMPs? (high
visibility recommended)
2
Construction
Access
Construction access is stabilized
with quarry spalls or equivalent
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
Control Flow
Rates
Are flow control measures installed
to control stormwater volumes and
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
Sediment
Controls
All perimeter sediment controls
(e.g. silt fence, wattles, compost
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
Stabilize
Soils
Have exposed un-worked soils
been stabilized with effective BMP
to prevent erosion and sediment
deposition?
Construction Stormwater Site Inspection Form
Page 3
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
5
Stabilize Soils
Cont.
Are stockpiles stabilized from erosion,
protected with sediment trapping
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?
6
Protect
Slopes
Has stormwater and ground water
been diverted away from slopes and
disturbed areas with interceptor dikes,
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
Drain Inlets
Storm drain inlets made operable
during construction are protected.
Are existing storm drains within the
influence of the project protected?
8
Stabilize
Channel and
Outlets
Have all on-site conveyance channels
been designed, constructed and
stabilized to prevent erosion from
expected peak flows?
Is stabilization, including armoring
material, adequate to prevent erosion
of outlets, adjacent stream banks,
slopes and downstream conveyance
systems?
9
Control
Pollutants
Are waste materials and demolition
debris handled and disposed of to
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?
Construction Stormwater Site Inspection Form
Page 4
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
9
Cont.
Wheel wash wastewater is handled
and disposed of properly.
10
Control
Dewatering
Concrete washout in designated areas.
No washout or excess concrete on the
ground.
Dewatering has been done to an
approved source and in compliance
with the SWPPP.
Were there any clean non turbid
dewatering discharges?
11
Maintain
BMP
Are all temporary and permanent
erosion and sediment control BMPs
maintained to perform as intended?
12
Manage the
Project
Has the project been phased to the
maximum degree practicable?
Has regular inspection, monitoring and
maintenance been performed as
required by the permit?
Has the SWPPP been updated,
implemented and records maintained?
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
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
Date
Initials
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: