23-101052-SU Construction SWPPP 2-28-23 February 15, 2023
Koval Short Plat
Construction Stormwater Pollution Prevention Plan
Applicant
Mr. Roman Koval
23118 126th Avenue Southeast
Kent, WA 98031
(206) 531-9287
romanrk@hotmail.com
Engineer
Valor Civil Engineering, PLLC
1009 North 9th Street
Tacoma, WA 98403
(253) 861-7741
valorcivilengineering@hotmail.com
Contact: Frank Marescalco, PE
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Project Engineer’s Certification
I hereby state that this technical information report has been prepared by me or under my
supervision and meets the standard of care and expertise which is usual and customary in this
community for professional engineers.
This report has been prepared for review by the City of Federal Way Department of Community
Development (City) in accordance with the 2016 King County Surface Water Design Manual as
amended by the City of Federal Way Addendum to the King County Surface Water Design Manual,
published January 8, 2017. This document is hereinafter referred to simply as the “Manual.”
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Table of Contents
Drainage Report
Section 1: Existing Conditions ..................................................................................................................................... 1
Section 2: Proposed Project Overview ..................................................................................................................... 1
Section 3: Erosion and Sediment Control Measures .......................................................................................... 1
1. Clearing Limits ................................................................................................................................................... 2
2. Cover Measures ................................................................................................................................................. 2
3. Perimeter Protection ....................................................................................................................................... 2
4. Traffic Area Stabilization ............................................................................................................................... 2
5. Sediment Retention ......................................................................................................................................... 3
6. Surface Water Collection ............................................................................................................................... 3
7. Dewatering Control .......................................................................................................................................... 3
8. Dust Control ........................................................................................................................................................ 3
9. Flow Control........................................................................................................................................................ 3
10. Protect Existing and Proposed Flow Control BMPs............................................................................ 3
11. Maintain BMPs ................................................................................................................................................... 3
12. Manage the Project ........................................................................................................................................... 4
13. Protect LID Measures ...................................................................................................................................... 4
Section 4: Stormwater Pollution Prevention and Spill Control Measures ................................................ 4
Section 5: Phasing and Schedule ................................................................................................................................ 5
Section 6: Financial/Ownership Responsibilities ............................................................................................... 5
Appendixes
Appendix A: Project Plans ........................................................................................................................................ A-1
Appendix B: Best Management Practices Standards and Specifications .............................................. B-1
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Section 1: Existing Conditions
The proposed project is located on King County parcel no. 7575600130. The address of the
property is 27634 25th Drive South, Federal Way, WA 98003. The site is about 16,860 square feet in
size and is zoned RS5.0. The lot has direct access to 25th Drive South which is a public paved street.
The lot is currently developed as a single-family residence.
Land cover at the site is a mixture of impervious surfaces, lawn and landscape areas, and more
heavily vegetated areas. The topography at the site is moderate to steeply sloped. The entire site is
considered to be an erosion hazard area due to the presence of erodible soils on moderate and
steep slopes.
The soil on-site is mapped by the USDA Web Soil Survey (WSS) as predominately glacial till. On-site
soil explorations confirmed that the site is characterstic of finer-grained till soils.
The site is surrounded on the north, east, and south by developed residential single-family lots. The
western boundary of the site is 25th Drive South.
To the best of our knowledge, the soil and groundwater at the site are not known to be
contaminated.
Section 2: Proposed Project Overview
The project proposes to subdivide the existing, developed single-family lot into two new lots. The
existing home will be retained and a new home will be built on the new vacant lot. The work
proposed for the short plat is quite limited, involving only the removal and replacement of portions
of a private driveway and public walk for the purposes of connecting to the City’s storm drainage
system.
Future work associated with actual build-out of the home will be examined in more detail as part of
the building permit application that will be filed once the short plat application has been approved.
The exact nature and extents of impacts to the site will be determined at that time. For the purposes
of this Construction SWPPP document, the work is limited to that which is necessary for short plat
approval only. No mass clearing or grading is anticipated.
Section 3: Erosion and Sediment Control Measures
This section outlines typical BMPs to be used on-site to satisfy the applicable erosion control
elements. The SWPPP is a living document intended to reflect both the initial design and changing
conditions throughout the life of the project. It may become necessary to implement additional
BMPs not listed below if project conditions warrant. Changes to the design or the means and
methods used by the contractor may also warrant a need for additional BMPs or may change those
of the elements that apply. The knowledgeable erosion and sediment control lead on-site should
document changes and update the SWPPP when there are deviations from the original design or
noted deficiencies in performance of those BMPs installed.
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For the convenience of the user, specifications and guidelines which have been prepared by King
County for the BMPs listed below and additional measures (if needed) are included in Appendix B
of this document.
Anticipated BMPs to satisfy each of the elements are identified in the list below, designated by their
corresponding notation in Appendix D of the Manual.
1. Clearing Limits
It is not necessary to formally mark clearing limits. The area of impact for this project is
only about 700 square feet.
2. Cover Measures
The following soil cover BMPs shall be implemented as needed at the site:
· D.2.1.2.1: Surface Roughening
· D.2.1.2.4: Plastic Covering
· D.2.1.2.5: Straw Wattles
· D.2.1.2.6: Temporary and Permanent Seeding
· D.2.1.2.7: Sodding
3. Perimeter Protection
Formal perimeter protection is not required. The only area where perimeter protection
could be installed is within a paved surface because that is the only part of the site
downslope of the disturbed area. The duration and extent of disturbance are both so limited
that perimeter protection is not merited.
4. Traffic Area Stabilization
The project does not include any areas on-site designated for construction traffic or parking.
The work area is so limited in physical extent that it can be completed from fully stabilized
surfaces without a need for equipment to enter or leave a disturbed, bare soil area.
If sediment is tracked onto City streets, the affected pavement shall be cleaned thoroughly.
Such cleaning shall be accomplished at least daily, or more often if conditions warrant or if
requested by the inspector. Sediment shall be removed from the road surface by shoveling,
sweeping, or other means of pick-up and shall be transported to a sediment disposal area.
Only after sediment has been removed shall street washing be conducted. Street washing
wastewater shall be contained and prevented from entering the public drainage system.
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5. Sediment Retention
A formal sediment trap is not needed for this project. Sediment can be retained on the site
through the use of proper erosion control practices.
6. Surface Water Collection
Formal surface water collection features are not necessary. There are no significant
upstream flows that need to be intercepted or rerouted around the site.
7. Dewatering Control
Dewatering is not anticipated because there are no indications of shallow groundwater in
the soil exploration efforts conducted at the site and no planned deep excavations.
8. Dust Control
Dust control is not likely to be a major factor for consideration. However, should dust
become a problem, the best way to handle it for this small site would be spraying water as
needed. Other methods are not likely to be required or warranted. Refer to Table D.2.1.8.A
of Appendix D of the KC SWMM for other methods.
9. Flow Control
This project is not required to construct formal flow control facilities, such as a detention
pond. The extent of disturbances is so small that there will be no impact to flows leaving the
site. In fact, since the majority of disturbed areas are pavement in their current condition, it
is likely that flows from the disturbed site would actually be less than those in the paved,
fully stabilized condition.
10. Protect Existing and Proposed Flow Control BMPs
There are no existing or proposed flow control BMPs for this project.
11. Maintain BMPs
Protection measures shall be monitored and inspected at least monthly during the dry
season and every two weeks during the wet season. Measures shall also be inspected within
24 hours of a major storm event.
1. Maintain and repair all temporary and permanent erosion and sediment control BMPs
as needed to assure continued performance of their intended function in accordance
with BMP specifications.
2. Remove all temporary erosion and sediment control BMPs prior to final construction
approval, or within 30 days after achieving final site stabilization or after the temporary
BMPs are no longer needed.
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3. Provide protection to all BMPs installed for the permanent control of stormwater from
sediment and compaction. All BMPs that are to remain in place following completion of
construction shall be examined and commissioned to full operating conditions. If
sediment enters the BMPs during construction, it shall be removed and the BMP shall be
returned to the conditions specified in the construction documents or as required for
full BMP replacement.
4. Remove or stabilize trapped sediment on-site. Permanently stabilize disturbed soil
resulting from the removal of BMPs or vegetation.
12. Manage the Project
The contractor shall designate a sediment and erosion control lead. Because this project
disturbs less than one acre, it is not necessary for this person to be a certified sediment and
erosion control lead. However, the designated individual must have the skills to assess the
following:
· Site conditions and construction activities that could impact the quality of
stormwater
· Effectiveness of erosion and sediment control measures used to control the quality
of stormwater discharges
· Presence of suspended sediment, turbidity, discoloration, and oil sheen in
stormwater
· Whether it is necessary to install, maintain, or repair BMPs to improve the quality of
stormwater discharges
The designated lead must be able to correct problems by:
· Reviewing the SWPPP for compliance with all construction SWPPP elements and
making appropriate revisions
· Addressing problems no later than within 10 days of identifying the problem
13. Protect Low-Impact Development Measures
Any part of the site which is impacted by construction and will remain pervious in its final
state must be amended per Department of Ecology and King County soil amendment
requirements. Typically, it is necessary to add compost to the existing soil. Construction
traffic should not be allowed in these areas following the application of soil amendments.
Soil amendments should be one of the last things done at the site prior to final stabilization
measures.
Section 4: Stormwater Pollution Prevention and Spill Control Measures
This section details means and methods that the contractor may use to comply with stormwater
pollution prevent and spill control measures. These are a collection of best practices that serve as
source control BMPs to prevent typical construction site pollutants, like oil and concrete, from
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entering runoff and escaping the site. They are designated by their notation in Appendix D of the
King County SWMM. These measures are intended broadly to achieve the following objectives:
1. Handle and dispose of potential sources of pollution without affecting stormwater quality
2. Provide cover and secondary containment for materials, fuels, and other kinds of pollutants
3. Implement spill prevention measures and, where spills do occur, contain and remediate
them expeditiously and effectively
4. Apply chemicals and fertilizers without causing adverse impacts to stormwater quality
5. Control pH-modifying sources of pollution, like concrete.
Because contractors accomplish tasks in different ways, the exact timing and method of
implementation of these BMPs will vary and is best left to the contractor to determine. Some of
these measures may not apply to every project. Except for very large projects, these measures
cannot be “designed.” The contractor or site operator will be held responsible for impacts to
downstream waters. Therefore, it is important to ensure that all staff and subcontractors
understand these best practices and apply them correctly.
The following are detailed best practices that can be found in the King County SWMM:
· D.2.2.1: Concrete Handling
· D.2.2.2: Concrete Wash-Out Area
· D.2.2.3: Sawcutting and Surfacing Pollution Prevention
· D.2.2.4: Material Delivery, Storage, and Containment
· D.2.2.5: Construction Stormwater Chemical Treatment
Section 5: Phasing and Schedule
The proposed project would be completed in a single phase. The construction would begin in
earnest on receipt of permits. It is estimated that construction would take one week or less.
Section 6: Financial/Ownership Responsibilities
The applicant has acknowledged the potential need for bonds or other financial securities and is
prepared to issue such securities if required by the City.
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Appendix A: Project Plans
Project plans have been prepared by the Owner/applicant and are provided as a separate, attached
document.
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Appendix B: Best Management Practices Standards and
Specifications
Attached
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-10
D.2.1.1 CLEARING LIMITS
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-11
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-12
D.2.1.2 COVER MEASURES
When to Install: Any exposed soils that will remain unworked for more than the time limit set above shall
be covered by the end of the working day. If the exposed area is to remain unworked for more than 30
days, the area shall be seeded with the temporary seed mix or an equivalent mix that will provide rapid
protection (see Section D.2.1.2.6). If the disturbed area is to remain unworked for a year or more or if the
area has reached final grade, permanent seed mix or an equivalent mix shall be applied.
Measures to Use: Cover methods include the use of surface roughening, mulch, erosion control nets and
blankets, plastic covering, seeding, and sodding. Mulch and plastic sheeting are primarily intended to
protect disturbed areas for a short period of time, typically days to a few months. Seeding and sodding are
measures for areas that are to remain unworked for months. Erosion nets and blankets are to be used in
conjunction with seeding steep slopes. The choice of measures is left to the designer; however, there are
restrictions on the use of these methods, which are listed in the "Conditions of Use" and the "Design and
Installation Specifications" sections for each measure.
The methods listed are by no means exhaustive. Variations on the standards presented here are
encouraged if other cost-effective products or methods provide substantially equivalent or superior
performance. Also, the details of installation can, and should, vary with the site conditions. A useful
reference on the application of cover measures in the Puget Sound area is Improving the Cost Effectiveness
of Highway Construction Site Erosion and Pollution Control, Horner, Guedry, and Kortenhof (1990).
D.2.1.2.1 SURFACE ROUGHENING
Purpose
The purpose of surface roughening is to aid in the establishment of vegetative cover and to reduce runoff
velocity, increase infiltration, and provide for sediment trapping through the provision of a rough soil
surface. The rough soil surface may be created by operating a tiller or other equipment on the contour to
form horizontal depressions or by leaving slopes in a roughened condition by not fine grading.
Conditions of Use
1. All slopes steeper than 3H:1V and greater than 5 vertical feet require surface roughening.
2. Areas with grades steeper than 3H:1V should be roughened to a depth of 2 to 4 inches prior to
seeding.
3. Areas that will not be stabilized immediately may be roughened to reduce runoff velocity until seeding
takes place.
4. Slopes with a stable rock face do not require roughening.
5. Slopes where mowing is planned should not be excessively roughened.
Design and Installation Specifications
There are different methods for achieving a roughened soil surface on a slope, and the selection of an
appropriate method depends upon the type of slope. Roughening methods include stair-step grading,
grooving, contour furrows, and tracking. See Figure D.2.1.2.A for information on tracking and contour
furrows. Factors to be considered in choosing a method are slope steepness, mowing requirements, and
whether the slope is formed by cutting or filling. Sole reliance on roughening for temporary erosion
control is of limited effectiveness in intense rainfall events. Stair-step grading may not be practical for
sandy, steep, or shallow soils.
1. Disturbed areas that will not require mowing may be stair-step graded, grooved, or left rough after
filling
2. Stair Step grading is particularly appropriate in soils containing large amounts of soft rock. Each
"step" catches material that sloughs from above, and provides a level site where vegetation can
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-13
SECTION D.2.1 ESC MEASURES
become established. Stairs should be wide enough to work with standard earth moving equipment.
Stair steps must be on contour or gullies will form on the slope.
3. Areas that will be mowed (slopes less steep than 3H:1V) may have small furrows left by disking,
harrowing, raking, or seed-planting machinery operated on the contour.
4. Graded areas with slopes greater than 3H:1V but less than 2H:1V should be roughened before
seeding. This can be accomplished in a variety of ways, including "track walking" or driving a
crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel to slope contours.
5. Tracking is done by operating equipment up and down the slope to leave horizontal depressions in the
soil.
Maintenance Standards
Periodically check roughened, seeded, planted, and mulched slopes for rills and gullies, particularly after a
significant storm event. Fill these areas slightly above the original grade, then re-seed and mulch as soon
as possible.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-14
D.2.1.2 COVER MEASURES
FIGURE D.2.1.2.A SURFACE ROUGHENING
50'(15
m
)
1
GROOVES WILL CATCH SEED,
FERTILIZER, MULCH, RAINFALL
AND DECREASE RUNOFF.
"TRACKING" WITH MACHINERY UP AND DOWN
THE SLOPE PROVIDES GROOVES THAT WILL CATCH
SEED, RAINFALL AND REDUCE RUNOFF.
CONTOUR FURROWS
TRACKING
6" MIN.
(150mm)
3 MAX.
SURFACE ROUGHENING BY TRACKING AND CONTOUR FURROWS
NTS
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-15
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-16
D.2.1.2 COVER MEASURES
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 Lake 7 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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-17
SECTION D.2.1 ESC MEASURES
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
4/24/2016 2016 Surface Water Design Manual – Appendix D D-18
D.2.1.2 COVER MEASURES
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-19
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-20
D.2.1.2 COVER MEASURES
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-21
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-22
D.2.1.2 COVER MEASURES
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-23
SECTION D.2.1 ESC MEASURES
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 DPER inspector. The DPER 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).
4/24/2016 2016 Surface Water Design Manual – Appendix D D-24
D.2.1.2 COVER MEASURES
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-25
SECTION D.2.1 ESC MEASURES
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
4/24/2016 2016 Surface Water Design Manual – Appendix D D-26
D.2.1.2 COVER MEASURES
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-27
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-28
D.2.1.2 COVER MEASURES
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-29
SECTION D.2.1 ESC MEASURES
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 DPER.
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-30
D.2.1.2 COVER MEASURES
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-31
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-32
D.2.1.3 PERIMETER PROTECTION
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-33
SECTION D.2.1 ESC MEASURES
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 not 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. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-34
D.2.1.3 PERIMETER PROTECTION
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-35
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-36
D.2.1.3 PERIMETER PROTECTION
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 drainage 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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-37
SECTION D.2.1 ESC MEASURES
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
4/24/2016 2016 Surface Water Design Manual – Appendix D D-38
D.2.1.3 PERIMETER PROTECTION
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-39
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-40
D.2.1.4 TRAFFIC AREA STABILIZATION
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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-41
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-42
D.2.1.4 TRAFFIC AREA STABILIZATION
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' MIN.
NOTES:
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-43
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-44
D.2.1.4 TRAFFIC AREA STABILIZATION
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, such as
a closed-loop recirculation system or land application, or to the sanitary sewer system with proper
local sewer district approval or permits.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-45
SECTION D.2.1 ESC MEASURES
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:
4/24/2016 2016 Surface Water Design Manual – Appendix D D-46
D.2.1.5 SEDIMENT RETENTION
D.2.1.5 SEDIMENT RETENTION
Surface water collected from disturbed areas of the site shall be routed through a sediment pond or trap
prior to release from the site. An exception is for areas at the perimeter of the site with drainage areas
small enough to be treated solely with perimeter protection (see Section D.2.1.3, p. D-33). Also, if the
soils and topography are such that no offsite discharge of surface water is anticipated up to and including
the developed 2-year runoff event, sediment ponds and traps are not required. A 10-year peak flow using
the approved model with 15-minute time steps shall be used for sediment pond/trap sizing if the project
size, expected timing and duration of construction, or downstream conditions warrant a higher level of
protection (see below). At the County's discretion, sites may be worked during the dry season without
sediment ponds and traps if there is some other form of protection of surface waters, such as a 100-foot
forested buffer between the disturbed areas and adjacent surface waters. For small sites, use the criteria
defined in Section D.2.1.3, Perimeter Protection to determine minimum flow path length. If the site work
has to be extended into the wet season, a back-up plan must be identified in the CSWPP plan and
implemented. Protection of catch basins is required for inlets that are likely to be impacted by sediment
generated by the project and that do not drain to an onsite sediment pond or trap. Sediment retention
facilities shall be installed prior to grading of any contributing area and shall be located so as to avoid
interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages.
Purpose: The purpose of sediment retention facilities is to remove sediment from runoff generated from
disturbed areas.
When to Install: The facilities shall be constructed as the first step in the clearing and grading of the site.
The surface water conveyances may then be connected to the facilities as site development proceeds.
Measures to Use: There are three sediment retention measures in this section. The first two, sediment
traps and ponds, serve the same function but for different size catchments. All runoff from disturbed areas
must be routed through a trap or pond except for very small areas at the perimeter of the site small enough
to be treated solely with perimeter protection (see Section D.2.1.3, p. D-33). The third measure is for
catch basin protection. It is only to be used in limited circumstances and is not a primary sediment
treatment facility. It is only intended as a backup in the event of failure of other onsite systems.
Use of Permanent Drainage Facilities: All projects that are constructing permanent facilities for runoff
quantity control are strongly encouraged to use the rough-graded or final-graded permanent facilities for
ponds and traps. This includes combined facilities and infiltration facilities. When permanent facilities
are used as temporary sedimentation facilities, the surface area requirements of sediment traps (for
drainages less than 3 acres) or sediment ponds (more than 3 acres) must be met. If the surface area
requirements are larger than the surface area of the permanent facility, then the pond shall be enlarged to
comply with the surface area requirement. The permanent pond shall also be divided into two cells as
required for sediment ponds. Either a permanent control structure or the temporary control structure
described in Section D.2.1.5.2 may be used. If a permanent control structure is used, it may be advisable
to partially restrict the lower orifice with gravel to increase residence time while still allowing dewatering
of the pond.
If infiltration facilities are to be used, the sides and bottom of the facility must only be rough excavated to
a minimum of three feet above final grade. Excavation should be done with a backhoe working at "arms
length" to minimize disturbance and compaction of the infiltration surface. Additionally, any required
pretreatment facilities shall be fully constructed prior to any release of sediment-laden water to the facility.
Pretreatment and shallow excavation are intended to prevent the clogging of soil with fines. Final grading
of the infiltration facility shall occur only when all contributing drainage areas are fully stabilized (see
Section D.2.4.5, p. D-115).
Selection of the Design Storm: In most circumstances, the developed condition 2-year peak flow using
the approved model with 15-minute time steps is sufficient for calculating surface area for ponds and traps
and for determining exemptions from the sediment retention and surface water collection requirements
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-47
SECTION D.2.1 ESC MEASURES
(Sections D.2.1.5 and D.2.1.6, respectively). In some circumstances, however, the approved model 10-
year 15-minute peak flow should be used. Examples of such circumstances include the following:
• Sites that are within ¼ mile of salmonid streams, wetlands, and designated sensitive lakes such as
Lake Sammamish
• Sites where significant clearing and grading is likely to occur during the wet season
• Sites with downstream erosion or sedimentation problems.
Natural Vegetation: Whenever possible, sediment-laden water shall be discharged into onsite, relatively
level, vegetated areas. This is the only way to effectively remove fine particles from runoff. This can be
particularly useful after initial treatment in a sediment retention facility. The areas of release must be
evaluated on a site-by-site basis in order to determine appropriate locations for and methods of releasing
runoff. Vegetated wetlands shall not be used for this purpose. Frequently, it may be possible to pump
water from the collection point at the downhill end of the site to an upslope vegetated area. Pumping shall
only augment the treatment system, not replace it because of the possibility of pump failure or runoff
volume in excess of pump capacity.
D.2.1.5.1 SEDIMENT TRAP
Code: ST Symbol:
Purpose
Sediment traps remove sediment from runoff originating from disturbed areas of the site. Sediment traps
are typically designed to only remove sediment as small as medium silt (0.02 mm). As a consequence,
they usually only result in a small reduction in turbidity.
Conditions of Use
A sediment trap shall be used where the contributing drainage area is 3 acres or less.
Design and Installation Specifications
1. See Figure D.2.1.5.A for details.
2. If permanent runoff control facilities are part of the project, they should be used for sediment retention
(see "Use of Permanent Drainage Facilities" on page D-47).
3. To determine the trap geometry, first calculate the design surface area (SA) of the trap, measured at the
invert of the weir. Use the following equation:
SA = FS(Q2/Vs)
where Q2 = Design inflow (cfs) from the contributing drainage area based on the developed
condition 2-year or 10-year peak discharge using the approved model with 15-minute
time steps as computed in the hydrologic analysis. The approved model 10-year 15-
minute peak flow shall be used if the project size, expected timing and duration of
construction, or downstream conditions warrant a higher level of protection, or if the
pond discharge path leaves the site (note provisions must made to prevent increases
in the existing site conditions 2-year and 10-year runoff peaks discharging from the
project site during construction, see Section D.3.9, Flow Control). If no hydrologic
analysis is required, the Rational Method may be used (Section 3.2.1 of the King
County Surface Water Design Manual).
4/24/2016 2016 Surface Water Design Manual – Appendix D D-48
D.2.1.5 SEDIMENT RETENTION
Vs = The settling velocity (ft/sec) of the soil particle of interest. The 0.02 mm (medium
silt) particle with an assumed density of 2.65 g/cm3 has been selected as the particle
of interest and has a settling velocity (Vs) of 0.00096 ft/sec.
FS = A safety factor of 2 to account for non-ideal settling.
Therefore, the equation for computing surface area becomes:
SA = 2 x Q2/0.00096 or 2080 square feet per cfs of inflow
Note: Even if permanent facilities are used, they must still have a surface area that is at least as large
as that derived from the above formula. If they do not, the pond must be enlarged.
4. To aid in determining sediment depth, all traps shall have a staff gage with a prominent mark one foot
above the bottom of the trap.
Maintenance Standards
1. Sediment shall be removed from the trap when it reaches 1 foot in depth.
2. Any damage to the trap embankments or slopes shall be repaired.
FIGURE D.2.1.5.A SEDIMENT TRAP
NOTE:
TRAP MAY BE FORMED BY BERM OR BY
PARTIAL OR COMPLETE EXCAVATION
3
H
:
1
V
M
A
X
.
FLAT BOTTOM
1' MIN.
18" MIN.
1' MIN.
1' MIN. DEPTH OVERFLOW SPILLWAY
CROSS SECTION
TRAP OUTLET
NATIVE SOIL OR
COMPACTED
BACKFILL
GEOTEXTILE
6' MIN.
MIN.1' DEPTH
2"-4" ROCK
MIN. 1' DEPTH 3/4"-1 1/2"
WASHED GRAVEL
4' MIN.
3.5'-5'
SURFACE AREA DETERMINED
AT TOP OF WEIR
DISCHARGE TO STABILIZED CONVEYANCE,
OUTLET OR LEVEL SPREADER
3/4"-1 1/2"
WASHED
GRAVEL GEOTEXTILE
2"-4" ROCK
RIPRAP
1' MIN. OVERFLOW
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-49
SECTION D.2.1 ESC MEASURES
D.2.1.5.2 SEDIMENT POND
Code: SP Symbol:
Purpose
Sediment ponds remove sediment from runoff originating from disturbed areas of the site. Sediment
ponds are typically designed to only remove sediment as small as medium silt (0.02 mm). As a
consequence, they usually reduce turbidity only slightly.
Conditions of Use
A sediment pond shall be used where the contributing drainage area is 3 acres or more.
Design and Installation Specifications
1. See Figure D.2.1.5.B, Figure D.2.1.5.C, and Figure D.2.1.5.D for details.
2. If permanent runoff control facilities are part of the project, they should be used for sediment retention
(see "Use of Permanent Drainage Facilities" on page D-47).
Determining Pond Geometry
1. Obtain the discharge from the hydrologic calculations for the 2-year and 10-year peak flows using the
approved model with 15-minute time steps (Q2 and Q10). The approved model 10-year 15-minute peak
flow shall be used if the project size, expected timing and duration of construction, or downstream
conditions warrant a higher level of protection, or if the pond discharge path leaves the site (note
provisions must made to prevent increases in the existing site conditions 2-year and 10-year runoff
peaks discharging from the project site during construction, see Section D.3.9, Flow Control). If no
hydrologic analysis is required, the Rational Method may be used (Section 3.2.1 of the King County
Surface Water Design Manual).
2. Determine the required surface area at the top of the riser pipe with the equation:
SA = 2 x Q10/0.00096 or 2080 square feet per cfs of inflow
See Section D.2.1.5.1 (p. D-48) for more information on the derivation of the surface area calculation.
3. The basic geometry of the pond can now be determined using the following design criteria:
• Required surface area SA (from Step 2 above) at top of riser
• Minimum 3.5-foot depth from top of riser to bottom of pond
• Maximum 3:1 interior side slopes and maximum 2:1 exterior slopes. The interior slopes may be
increased to a maximum of 2:1 if fencing is provided at or above the maximum water surface
• One foot of freeboard between the top of the riser and the crest of the emergency spillway
• Flat bottom
• Minimum one foot deep spillway
• Length-to-width ratio between 3:1 and 6:1.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-50
D.2.1.5 SEDIMENT RETENTION
Sizing of Discharge Mechanisms
Principal Spillway: Determine the required diameter for the principal spillway (riser pipe). The diameter
shall be the minimum necessary to pass the developed condition 10-year peak flow using the approved
model with 15-minute time steps (Q10). Use Figure 5.1.4.H (SWDM Chapter 5) to determine this
diameter (h = one foot). Note: A permanent control structure may be used instead of a temporary riser.
Emergency Overflow Spillway: Determine the required size and design of the emergency overflow
spillway for the developed condition 100-year approved model 15-minute peak flow using the procedure
in Section 5.1.1 ("Emergency Overflow Spillway" subsection) of the King County Surface Water Design
Manual.
Dewatering Orifice: Determine the size of the dewatering orifice(s) (minimum 1-inch diameter) using a
modified version of the discharge equation for a vertical orifice and a basic equation for the area of a
circular orifice.
1. Determine the required area of the orifice with the following equation:
hATg
hAA sso)10(81.43600x6.0
)2(6
5.0
5.0 −==
where Ao = orifice area (square feet)
As = pond surface area (square feet)
h = head of water above orifice (height of riser in feet)
T = dewatering time (24 hours)
g = acceleration of gravity (32.2 feet/second2)
2. Convert the required surface area to the required diameter D (inches) of the orifice:
o
o AADx54.13x24==π
3. The vertical, perforated tubing connected to the dewatering orifice must be at least 2 inches larger in
diameter than the orifice to improve flow characteristics. The size and number of perforations in the
tubing should be large enough so that the tubing does not restrict flow. The flow rate should be
controlled by the orifice.
Additional Design Specifications
• The pond shall be divided into two roughly equal volume cells by a permeable divider that will
reduce turbulence while allowing movement of water between cells. The divider shall be at least one-
half the height of the riser and a minimum of one foot below the top of the riser. Wire-backed, 2- to
3-foot high, extra strength filter fabric (see Section D.2.1.3.1) supported by treated 4"x4"s may be
used as a divider. Alternatively, staked straw bales wrapped with filter fabric (geotextile) may be
used.
If the pond is more than 6 feet deep, a different mechanism must be proposed. A riprap embankment
is one acceptable method of separation for deeper ponds. Other designs that satisfy the intent of this
provision are allowed as long as the divider is permeable, structurally sound, and designed to prevent
erosion under or around the barrier.
• To aid in determining sediment depth, one-foot intervals shall be prominently marked on the riser.
• If an embankment of more than 6 feet is proposed, the pond must comply with the criteria under
"Embankments" in Section 5.1.1 of the Surface Water Design Manual.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-51
SECTION D.2.1 ESC MEASURES
Maintenance Standards
1. Sediment shall be removed from the pond when it reaches 1 foot in depth.
2. Any damage to the pond embankments or slopes shall be repaired.
FIGURE D.2.1.5.B SEDIMENT POND PLAN VIEW
INFLOW
NOTE:
POND MAY BE FORMED BY BERM OR BY
PARTIAL OR COMPLETE EXCAVATION
DISCHARGE TO
STABILIZED
CONVEYANCE,
OUTLET OR LEVEL
SPREADER
EMERGENCY
OVERFLOW
SPILLWAY
KEY DIVIDER INTO SLOPE TO
PREVENT FLOW AROUND SIDES
THE POND LENGTH SHALL
BE 3 TO 6 TIMES THE
MAXIMUM POND WIDTH
SILT FENCE OR
EQUIVALENT
DIVIDER
RISER
PIPE
POND LENGTH
FIGURE D.2.1.5.C SEDIMENT POND CROSS SECTION
3H
:
1V
MAX
.
RISER PIPE (PRINCIPAL
SPILLWAY) OPEN AT TOP WITH
TRASH RACK PER FIG. 5.1.1.C
DEWATERING
DEVICE (SEE
RISER DETAIL)
2H
:
1VMAX.3H:1VMAX.WIRE-BACKED SILT
FENCE, STAKED STRAW
BALES WRAPPED WITH
FILTER FABRIC, OR
EQUIVALENT DIVIDER
CONCRETE BASE
(SEE RISER DETAIL)
DISCHARGE TO STABILIZED
CONVEYANCE, OUTLET OR
LEVEL SPREADER
DEWATERING
ORIFICE
CREST OF
EMERGENCY
SPILLWAY
1'
6' MIN. BERM WIDTH
EMBANKMENT
COMPACTED 95%
MODIFIED PROCTOR.
PERVIOUS MATERIALS
SUCH AS GRAVEL OR
CLEAN SAND SHALL
NOT BE USED.
1' MIN.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-52
D.2.1.5 SEDIMENT RETENTION
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-53
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-54
D.2.1.5 SEDIMENT RETENTION
• 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.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-55
SECTION D.2.1 ESC MEASURES
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
4/24/2016 2016 Surface Water Design Manual – Appendix D D-56
D.2.1.5 SEDIMENT RETENTION
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:
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-57
SECTION D.2.1 ESC MEASURES
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:
4/24/2016 2016 Surface Water Design Manual – Appendix D D-58
D.2.1.6 SURFACE WATER COLLECTION
D.2.1.6 SURFACE WATER COLLECTION
All surface water from disturbed areas shall be intercepted, conveyed to a sediment pond or trap, and
discharged downslope of any disturbed areas. An exception is for areas at the perimeter of the site with
drainage areas small enough to be treated solely with perimeter protection (see Section D.2.1.3). Also, if
the soils and topography are such that no offsite discharge of surface water is anticipated up to and
including the developed 2-year runoff event, surface water controls are not required. A 10-year approved
model 15-minute peak flow shall be used for sizing surface water controls if the project size, expected
timing and duration of construction, or downstream conditions warrant a higher level of protection (see the
introduction to Section D.2.1.5). At the County's discretion, sites may be worked during the dry season
without surface water controls, if there is some other form of protection of surface waters, such as a 100-
foot forested buffer between the disturbed areas and adjacent surface waters. Significant sources of
upslope surface water that drain onto disturbed areas shall be intercepted and conveyed to a stabilized
discharge point downslope of the disturbed areas. Surface water controls shall be installed concurrently
with rough grading.
Purpose: The purpose of surface water control is to collect and convey surface water so that erosion is
minimized, and runoff from disturbed areas is treated by a sediment pond or trap. Surface water control
essentially consists of three elements:
1. Interception of runoff on and above slopes
2. Conveyance of the runoff to a sediment pond or trap (if the runoff was collected from a disturbed
area)
3. Release of the runoff downslope of any disturbed areas.
When to Install: Surface water controls shall be constructed during the initial grading of an area and must
be in place before there is any opportunity for storm runoff to cause erosion.
Measures to Install: Interceptor dikes/swales intercept runoff, ditches and pipe slope drains convey the
runoff, and riprap or level spreaders help release the runoff in a non-erosive manner. Each measure is to
be used under different circumstances so there is very little overlap. However, the two options for
releasing water in a non-erosive manner, outlet protection and level spreaders, can be somewhat
interchangeable. See Figure D.2.1.6.A for a schematic drawing demonstrating the use of these measures.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-59
SECTION D.2.1 ESC MEASURES
FIGURE D.2.1.6.A SKETCH PLAN OF SURFACE WATER CONTROLS
D.2.1.6.1 INTERCEPTOR DIKE AND SWALE
Code: ID or IS Symbol: or
Purpose
Interceptor dikes and swales intercept storm runoff from drainage areas on or above disturbed slopes and
convey it to a sediment pond or trap. They may also be used to intercept runoff from undisturbed areas
and convey the runoff to a point below any exposed soils. Interception of surface water reduces the
possibility of slope erosion. Interceptor dikes and swales differ from ditches (see Section D.2.1.6.4) in
that they are intended to convey smaller flows along low-gradient drainage ways to larger conveyance
systems such as ditches or pipe slope drains.
Conditions of Use
Interceptor dikes and swales are required in the following situations:
1. At the top of all slopes in excess of 3H:1V and with more than 20 feet of vertical relief.
2. At intervals on any slope that exceeds the dimensions specified in this section for the horizontal
spacing of dikes and swales.
Design and Installation Specifications
1. See Figure D.2.1.6.B for details of an interceptor dike and Figure D.2.1.6.C for an interceptor swale.
INTERCEPTOR DIKE
TOP OF SLOPE
TOE OF SLOPE
OUTLET
PROTECTION
DITCH
SEDIMENT POND
SILT FENCE
STREAM
PIPE SLOPE DRAIN
FLOW
ID
PD
ID
OP
DI
SP
SF
SF
OP
4/24/2016 2016 Surface Water Design Manual – Appendix D D-60
D.2.1.6 SURFACE WATER COLLECTION
2. Interceptor dikes and swales shall be spaced horizontally as follows:
Average Slope Slope Percent Flowpath Length
20H:1V or less 3-5% 300 feet
(10 to 20)H:1V 5-10% 200 feet
(4 to 10)H:1V 10-25% 100 feet
(2 to 4)H:1V 25-50% 50 feet
3. For slopes steeper than 2H:1V with more than 10 feet of vertical relief, benches may be constructed
or closer spaced interceptor dikes or swales may be used. Whichever measure is chosen, the spacing
and capacity of the measures must be designed by the engineer and the design must include provisions
for effectively intercepting the high velocity runoff associated with steep slopes.
4. If the dike or swale intercepts runoff from disturbed areas, it shall discharge to a stable conveyance
system that routes the runoff to a sediment pond or trap (see Section D.2.1.5). If the dike or swale
intercepts runoff that originates from undisturbed areas, it shall discharge to a stable conveyance
system that routes the runoff downslope of any disturbed areas and releases the water at a stabilized
outlet.
5. Construction traffic over temporary dikes and swales shall be minimized.
Maintenance Standards
1. Damage resulting from runoff or construction activity shall be repaired immediately.
2. If the facilities do not regularly retain storm runoff, the capacity and/or frequency of the dikes/swales
shall be increased.
FIGURE D.2.1.6.B INTERCEPTOR DIKE
FIGURE D.2.1.6.C INTERCEPTOR SWALE
DIKE SPACING DEPENDS ON SLOPE GRADIENT
2' MIN.18" MIN.
2 MAX.
12 MAX.
1
DIKE MATERIAL COMPACTED
90% MODIFIED PROCTOR
SWALE SPACING DEPENDS ON SLOPE GRADIENT
2' MIN.
1' MIN.
LEVEL BOTTOM
2:1 MAX. SLOPE
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-61
SECTION D.2.1 ESC MEASURES
D.2.1.6.2 PIPE SLOPE DRAINS
Code: PD Symbol:
Purpose
Pipe slope drains are designed to carry concentrated runoff down steep slopes without causing erosion, or
saturation of slide-prone soils. Pipe slope drains may be used to divert water away from or over bare soil
to prevent gullies, channel erosion, and saturation of slide prone soils
Conditions of Use
Pipe slope drains should be used when a temporary or permanent stormwater conveyance is needed to
move water down a steep slope to avoid erosion. Pipe slope drains may be:
1. Connected to new catch basins and used temporarily until all permanent piping is installed.
2. Used on any slope with a gradient of 2H:1V or greater and with at least 10 feet of vertical relief.
3. Used to drain water collected from aquifers exposed on cut slopes and convey it to the base of the
slope.
4. Used to collect clean runoff from plastic sheet cover and direct away from any exposed soils.
5. Installed in conjunction with silt fence to drain collected water to a controlled area.
6. Used to divert small seasonal streams away from construction. Pipe slope drains have been used
successfully on culvert replacement and extension projects. Large flex pipe may be used on larger
streams during culvert removal, repair, or replacement.
7. Connected to existing downspouts and roof drains used to divert water away from work areas during
building renovation, demolition, and construction projects.
8. Rock-lined ditches or other permanent, non-erosive conveyances used to convey runoff down steep
slopes that are not steep slope hazard areas.
Design and Installation Specifications
1. See Figure D.2.1.6.D for details.
2. The capacity for temporary drains shall be sufficient to handle the developed 10-year peak flow using
the approved model with 15-minute time steps. Up to 30,000 square feet may be drained by each 6-
inch minimum diameter pipe without computation of the peak flow. Up to 2 acres may be drained by
each 12-inch minimum diameter pipe. Otherwise, the peak flow will need to be computed using the
Rational Method described in Section 3.2.1 of the King County Surface Water Design Manual
(SWDM).
3. The maximum drainage area allowed for any sized pipe is 10 acres. For larger areas, more than one
pipe shall be used or a rock-lined channel shall be installed (see SWDM Section 4.4.1, "Open
Channels").
4. The soil around and under the pipe and entrance section shall be thoroughly compacted.
5. The flared inlet section shall be securely connected to the slope drain and be fused or welded, or
have flange-bolted mechanical joints to ensure a watertight seal. Ensure that the entrance area is
stable and large enough to direct flow into the pipe.
6. Slope drains shall be continuously fused, welded, or flange-bolted mechanical joint pipe systems with
proper anchoring to the soil.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-62
D.2.1.6 SURFACE WATER COLLECTION
7. Where slope drains cross steep slope hazard areas or their associated buffers, the installation shall be
on the ground surface, accomplished with minimum alteration. In most circumstances, this requires
that slope drains be constructed of corrugated metal, CPE, or equivalent pipe and installed by hand
(see SWDM Section 4.2.1). Any area disturbed during installation or maintenance must be
immediately stabilized.
8. If the pipe slope drain will convey sediment-laden runoff, the runoff must be directed to a sediment
retention facility (see Section D.2.1.5). If the runoff is not from a disturbed area or is conveyed from a
sediment trap or pond, it must be conveyed to a stabilized discharge point (see Section D.2.1.6.5).
9. Re-establish cover immediately on areas disturbed by the installation.
Maintenance Standards
1. The inlet shall not be undercut or bypassed by water. If there are problems, the head wall shall be
appropriately reinforced.
2. No erosion shall occur at the outlet point. If erosion occurs, additional protection shall be added.
FIGURE D.2.1.6.D PIPE SLOPE DRAIN
INLET AND ALL SECTIONS
MUST BE SECURELY
FASTENED TOGETHER
WITH GASKETED
WATERTIGHT FITTINGS
DIKE MATERIAL COMPACTED
90% MODIFIED PROCTOR
CPE PIPE (LINED OR
UNLINED) OR EQUIVALENT
INTERCEPTOR
DIKE
INTERCEPTOR
DIKE
PROVIDE RIPRAP PAD OR
EQUIVALENT ENERGY
DISSIPATION
DISCHARGE TO A STABILIZED
WATERCOURSE, SEDIMENT
RETENTION FACILITY OR
STABILIZED OUTLET
STANDARD
FLARED
END SECTION
12"
MIN.
D.2.1.6.3 SUBSURFACE DRAINS
Purpose
To intercept, collect, and convey ground water to a satisfactory outlet, using a perforated pipe or conduit
below the ground surface. Subsurface drains are also known as "French Drains." The perforated pipe
provides a dewatering mechanism to drain excessively wet soils, provide a stable base for construction,
improve stability of structures with shallow foundations, or to reduce hydrostatic pressure and to improve
slope stability.
Conditions of Use
Use when excessive water must be removed from the soil. The soil permeability, depth to water table, and
impervious layers are all factors that may govern the use of subsurface drains.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-63
SECTION D.2.1 ESC MEASURES
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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-64
D.2.1.6 SURFACE WATER COLLECTION
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
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-65
SECTION D.2.1 ESC MEASURES
D.2.1.6.5 OUTLET PROTECTION
Code: OP Symbol:
Purpose
Outlet protection prevents scour at conveyance outlets.
Conditions of Use
Outlet protection is required at the outlets of all ponds, pipes, ditches, or other approved conveyances, and
where runoff is conveyed to a natural or manmade drainage feature such as a stream, wetland, lake, or
ditch.
Design and Installation Specifications
For the standard pipe slope drains in Section D.2.1.6.2 and other smaller conveyance systems, the standard
rock pad (6 feet by 8 feet) made of 1-foot thick quarry spall is adequate. For all other outlets, the outlet
protection shall meet the requirements of the "Outfalls" section of Core Requirement #4 and Section 4.2.2
of the King County Surface Water Design Manual.
Maintenance Standards for Outlet Protection
If there is scour at the outlet, the eroded area shall be protected with more conservative measures proposed
by the design engineer and approved by King County.
D.2.1.6.6 LEVEL SPREADER
Code: LS Symbol:
Purpose
Level spreaders convert concentrated runoff to sheet flow and release it onto areas stabilized by existing
vegetation.
Conditions of Use
Level spreaders may be used where runoff from undisturbed areas or sediment retention facilities is
discharged. This practice applies only where the spreader can be constructed on undisturbed soil and the
area below the level lip is vegetated and low gradient (see below).
Note: Level spreaders are conceptually an ideal way to release stormwater since the vegetation and soil
allow for the removal of fines from runoff that cannot be removed by settling or filtration. Unfortunately,
the performance record of spreaders in the field is dismal. They are frequently under-designed and,
despite the best installations, are rarely perfectly level, which results in the release of stormwater at a
particular point. This concentrated runoff can result in catastrophic erosion downslope. Given such
design failures, the use of spreaders is not encouraged. However, where slopes are gentle and the water
volume is relatively low, spreaders may still be the best method. When proposing their use, the designer
shall carefully evaluate the site for possible concerns.
Design and Installation Specifications
1. See Figure D.2.1.6.F for detail. Other designs may be used subject to County approval.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-66
D.2.1.6 SURFACE WATER COLLECTION
2. If runoff velocity as it enters the level spreader is more than 4 fps for the developed condition10-year
approved model 15-minute peak flow, a riprap apron must be provided to dissipate energy before the
runoff enters the spreader (Section D.2.1.6.5).
3. The total spreader length shall be at least the square root of the catchment area. The maximum
length for an individual spreader is 50 feet, limiting the catchment area that a single spreader may
serve to 2500 square feet. Although this is very small, four 50-foot level spreaders next to one another
could serve nearly an acre (40,000 square feet). Multiple spreaders shall not be placed uphill or
downhill from one another in a configuration that would allow water released from one spreader to
enter a downslope spreader.
4. The area below the spreader for a horizontal distance of 100 feet shall not exceed 20 percent and shall
be completely vegetated with no areas of instability or erosion. The topography for a horizontal
distance of 50 feet below the spreader shall be uniform so that runoff is not funneled into a swale or
channel immediately after its release.
5. The level spreader shall be seeded and mulched in accordance with Section D.2.1.2 (p. D-12).
Maintenance Standards
1. Any damage to the spreader shall be immediately repaired. Assure flows do not bypass the spreader at
the ends of the spreader.
2. The downslope area shall be checked for signs of erosion and to verify that the spreader is not
functioning as a point discharge. Any eroded areas shall be immediately stabilized, and the cause
determined and eliminated if possible. If the erosion is recurrent and the design, even when properly
installed and maintained, is not adequate to prevent erosion, a new method of releasing runoff shall be
installed in accordance with the standards of this appendix. Any new design must be approved by
King County.
FIGURE D.2.1.6.F LEVEL SPREADER
SPREADER MUST BE LEVEL
18" MIN. REBAR SUPPORTS
8' MIN. SPACING
CROSS SECTION
DETAIL OF SPREADER
DENSELY VEGETATED FOR
A MIN. OF 100' AND SLOPE
LESS THAN 5:1
PRESSURE-TREATED
2"X10"
3' MIN.
TREATED 2"x10" MAY BE ABUTTED END TO
END FOR MAX. SPREADER LENGTH OF 50'
6" MIN.
6" MIN.1" MIN.2H:1V MAX.1' MIN.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-67
SECTION D.2.1 ESC MEASURES
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-74), SWPPS Measures.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-68
D.2.1.8 DUST CONTROL
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 DPER inspector assigned to specific projects.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-69
SECTION D.2.1 ESC MEASURES
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
4/24/2016 2016 Surface Water Design Manual – Appendix D D-70
D.2.1.9 FLOW CONTROL
D.2.1.9 FLOW CONTROL
Surface water from disturbed areas must be routed through the project's onsite flow control facility or
other provisions must made to prevent increases in the existing site conditions 2-year and 10-year runoff
peaks discharging from the project site during construction.
Purpose: The purpose of surface water flow control is to mitigate increases in runoff peaks that occur
during construction as a result of clearing vegetation, compacting the soil, and adding impervious surface.
Such increases can cause or aggravate downstream flooding and erosion.
When to Install: Surface water flow control shall be installed or otherwise provided prior to any clearing
and/or grading of the site, except that required to construct the surface water flow control facilities.
Measures to Use: The project's onsite flow control facility or other equivalent storage facility that meets
the peak-matching performance criteria stated above.
D.2.1.10 PROTECT EXISTING AND PROPOSED FLOW CONTROL BMPS
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.
Purpose: The purpose of protecting existing and proposed flow control BMP areas is to avoid
sedimentation and soil compaction that would adversely affect infiltration, and also avoid contamination
by other pollutants.
When to Install: Flow control BMP area protection shall be installed or otherwise provided prior to any
clearing and/or grading of the site, except that required to construct flow control BMPs.
Measures to Use:
1. Protect all flow control BMPs and proposed BMP footprints from sedimentation through installation
and maintenance of erosion and sediment control BMPs on portions of the site that drain into the flow
control BMPs.
2. BMPs shall be restored to their fully functioning condition if they accumulate sediment during
construction. Restoring the BMP shall include, at a minimum, removal of sediment and any sediment-
laden bioretention soils, and replacing the removed soils with soils meeting the design specification.
Replacement with a new fully-functioning BMP may be required if restoration to the fully-functioning
condition can’t be accomplished.
3. Prevent compacting Bioretention BMPs by excluding construction equipment and foot traffic. Protect
completed lawn and landscaped areas from compaction due to construction equipment.
4. Control erosion and avoid introducing sediment from surrounding land uses onto permeable
pavements. Do not allow muddy construction equipment on the base material or pavement. Do not
allow sediment-laden runoff onto permeable pavements.
5. Pavements fouled with sediments or no longer passing an initial infiltration text must be cleaned using
procedures from the local stormwater manual or the manufacturer’s procedures.
6. Keep all heavy equipment off existing soils under flow control BMPs that have been excavated to
final grade to retain the infiltration rate of the soils.
Additional Guidance
See Chapter 5: Precision Site Preparation and Construction in the LID Technical Guidance Manual for
Puget Sound for more detail on protecting LID integrated management practices. Note that the LID
Technical Guidance Manual for Puget Sound (2012) is for additional informational purposes only. The
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-71
SECTION D.2.1 ESC MEASURES
guidance within this manual must be followed if there are any discrepancies between this manual and the
LID Technical Guidance Manual for Puget Sound (2012).
D.2.1.11 MAINTAIN PROTECTIVE 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.
Purpose: The purpose of maintaining protective BMPs is to provide continuous erosion and sediment
control protection throughout the life of the project, and avoid sedimentation, soil compaction and
contamination by other pollutants that would adversely affect infiltration and surface runoff.
When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum, and
promptly maintained to fully functioning condition as necessary to assure continued performance of their
intended function.
Measures to Use:
1. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to
assure continued performance of their intended function in accordance with BMP specifications.
2. Remove all temporary erosion and sediment control BMPs prior to final construction approval, or
within 30 days after achieving final site stabilization or after the temporary BMPs are no longer
needed.
3. Provide protection to all BMPs installed for the permanent control of stormwater from sediment and
compaction. All BMPs that are to remain in place following completion of construction shall be
examined and placed in full operating conditions. If sediment enters the BMPs during construction, it
shall be removed and the BMP shall be returned to the conditions specified in the construction
documents or as required for full BMP replacement.
4. Remove or stabilize trapped sediment on site. Permanently stabilize disturbed soil resulting from
removal of BMPs or vegetation.
D.2.1.12 MANAGE THE PROJECT
Coordination and timing of site development activities relative to ESC concerns (Section D.2.4), and
timely inspection, maintenance and update of protective measures (Section D.2.3) are necessary to
effectively manage the project and assure the success of protective ESC and SWPPS design and
implementation.
Projects shall assign a qualified CSWPP Supervisor (Section D.2.3.1) to be the primary contact for ESC
and SWPPP issues and reporting, coordination with subcontractors and implementation of the CSWPP
plan as a whole.
Measures to Use:
1. Phase development projects to the maximum degree practicable and take into account seasonal work
limits.
2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued
performance of their intended function. Conduct site inspections and monitoring in accordance with
the Construction Stormwater General Permit and King County requirements.
3. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in
accordance with the Construction Stormwater General Permit and King County requirements.
4. Projects that disturb one or more acres must have, site inspections conducted by a Certified Erosion
and Sediment Control Lead (CESCL) (see Section D.2.3.1). Project sites less than one acre (not part
4/24/2016 2016 Surface Water Design Manual – Appendix D D-72
D.2.2.1 CONCRETE HANDLING
of a larger common plan of development or sale) may have a person without CESCL certification
conduct inspections. By the initiation of construction, the SWPPP must identify the CESCL or
inspector, who shall be present on-site or on-call at all times.
The CESCL or inspector (project sites less than one acre) must have the skills to assess the:
• Site conditions and construction activities that could impact the quality of stormwater.
• Effectiveness of erosion and sediment control measures used to control the quality of stormwater
discharges.
• The CESCL or inspector must examine stormwater visually for the presence of suspended
sediment, turbidity, discoloration, and oil sheen. They must evaluate the effectiveness of BMPs
and determine if it is necessary to install, maintain, or repair BMPs to improve the quality of
stormwater discharges.
Based on the results of the inspection, construction site operators must correct the problems identified
by:
• Reviewing the SWPPP for compliance with all construction SWPPP elements and making
appropriate revisions within 7 days of the inspection.
• Immediately beginning the process of fully implementing and maintaining appropriate source
control and/or treatment BMPs as soon as possible, addressing the problems not later than within
10 days of the inspection. If installation of necessary treatment BMPs is not feasible within 10
days, the construction site operator may request an extension within the initial 10-day response
period.
• Documenting BMP implementation and maintenance in the site log book (applies only to sites
that have coverage under the Construction Stormwater General Permit).
• The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs, and
all stormwater discharge points at least once every calendar week and within 24 hours of any
discharge from the site. (For purposes of this condition, individual discharge events that last more
than one day do not require daily inspections. For example, if a stormwater pond discharges
continuously over the course of a week, only one inspection is required that week.) The CESCL
or inspector may reduce the inspection frequency for temporary stabilized, inactive sites to once
every calendar month
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-73
SECTION D.2.2 SWPPS MEASURES
D.2.2 SWPPS MEASURES
This section details the SWPPS measures that 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.. These SWPPS measures represent Best Management Practices (BMPs)8 for the control of
pollutant drips and spills as well as other impacts related to construction such as increased pH in concrete
construction and handling activities. Compliance with each of the SWPPS measures, and with any
project-specific control measures, to the extent applicable and necessary to meet the performance criteria
in Section D.2.2, and compliance with the CSWPP implementation requirements in Section D.2.4,
constitutes overall compliance with King County's CSWPP 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 SWPPS measure are divided into four sections:
1. Purpose
2. Conditions of Use
3. Design and Installation Specifications
4. Maintenance Requirements.
Note that the "Conditions of Use" always refers to site conditions. As site conditions change, SWPPS
measures must be changed to remain in compliance with the requirements of this appendix.
Whenever compliance with King County SWPPS Standards is required, all of the following SWPPS
measures must be considered for application to the project site as detailed in the following sections. The
construction pollutant generating concerns addressed by the BMPs that follow include:
• Concrete handling, washout and disposal(specifically portland cement concrete)
• Sawcutting and surfacing activities
• Materials delivery, storage and containment
• Filtration and chemical treatment of construction water to facilitate disposal or discharge to
approved locations
• Reporting requirements and documentation availability for specific BMP processes
Additionally, several of the ESC BMPs described in Section D.2.1 can be applicable to the SWPPS plan,
e.g., use of cover, fencing and access protection to protect temporary materials storage locations. The
applicant’s material supplier may be a resource (subject to King County approval) for BMPs to address
specific project applications or proposals. Conditions of approval on adjustments may also specify
additional requirements for the SWPPS plan.
8 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.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-74
D.2.2.1 CONCRETE HANDLING
D.2.2.1 CONCRETE HANDLING
Purpose
Concrete work can generate process water and slurry that contain fine particles and high pH, both of
which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to
surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete
process water, and concrete slurry from entering waters of the state.
Conditions of Use
Any time concrete is used, utilize these management practices. Concrete construction projects include, but
are not limited to, curbs, sidewalks, roads, bridges, foundations, floors, stormwater vaults, retaining walls,
driveways and runways.
Design and Installation Specifications
1. Assure that washout of concrete trucks, chutes, pumps, and internals is performed at an approved off-
site location or in designated concrete washout areas. Do not wash out concrete trucks onto the
ground, or into storm drains, open ditches, streets, or streams. Refer to BMP D.2.2.2 (p. D-76) for
information on concrete washout areas.
2. Return unused concrete remaining in the truck and pump to the originating batch plant for recycling.
Do not dump excess concrete on site, except in designated concrete washout areas.
3. Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into
formed areas only.
4. Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to
natural or constructed stormwater conveyances.
5. Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural
or constructed stormwater conveyances.
6. Contain washwater and leftover product in a lined container when no formed areas are available,.
Dispose of contained concrete in a manner that does not violate ground water or surface water quality
standards.
7. Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface
waters.
8. Refer to BMPs D.2.2.7 and D.2.2.8 for pH adjustment requirements.
9. Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project
involves one of the following activities:
• Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete
used over the life of a project).
• The use of engineered soils amended with (but not limited to) Portland cement-treated base,
cement kiln dust or fly ash.
• Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and repair the same day.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-75
SECTION D.2.2 SWPPS MEASURES
D.2.2.2 CONCRETE WASHOUT AREA
Purpose
Prevent or reduce the discharge of pollutants to stormwater from concrete waste by conducting washout
off-site, or performing on-site washout in a designated area to prevent pollutants from entering surface
waters or ground water.
Conditions of Use
Concrete washout area best management practices are implemented on construction projects where:
• Concrete is used as a construction material
• It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant, etc.).
• Concrete trucks, pumpers, or other concrete coated equipment are washed on-site.
Note: If less than 10 concrete trucks or pumpers need to be washed out on-site, the washwater may be
disposed of in a formed area awaiting concrete or an upland disposal site where it will not contaminate
surface or ground water. The upland disposal site shall be at least 50 feet from sensitive areas such as
storm drains, open ditches, or water bodies, including wetlands.
Design and Installation Specifications
Implementation
The following steps will help reduce stormwater pollution from concrete wastes:
1. Perform washout of concrete trucks at an approved off-site location or in designated concrete washout
areas only.
2. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or
streams.
3. Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas.
4. Concrete washout areas may be prefabricated concrete washout containers, or self-installed structures
(above-grade or below-grade).
5. Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies
may offer delivery service and provide regular maintenance and disposal of solid and liquid waste.
6. If self-installed concrete washout areas are used, below-grade structures are preferred over above-
grade structures because they are less prone to spills and leaks.
7. Self-installed above-grade structures should only be used if excavation is not practical.
Education
1. Discuss the concrete management techniques described in this BMP with the ready-mix concrete
supplier before any deliveries are made.
2. Educate employees and subcontractors on the concrete waste management techniques described in this
BMP.
3. Arrange for contractor’s superintendent or Certified Erosion and Sediment Control Lead (CESCL) to
oversee and enforce concrete waste management procedures.
4. A sign should be installed adjacent to each temporary concrete washout facility to inform concrete
equipment operators to utilize the proper facilities.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-76
D.2.2.2 CONCRETE WASHOUT AREA
Contracts
Incorporate requirements for concrete waste management into concrete supplier and subcontractor
agreements.
Location and Placement
1. Locate washout area at least 50 feet from sensitive areas such as storm drains, open ditches, or water
bodies, including wetlands.
2. Allow convenient access for concrete trucks, preferably near the area where the concrete is being
poured.
3. If trucks need to leave a paved area to access washout, prevent track-out with a pad of rock or quarry
spalls (see BMP D.2.1.4.2 (p. D-44)). These areas should be far enough away from other construction
traffic to reduce the likelihood of accidental damage and spills.
4. The number of facilities you install should depend on the expected demand for storage capacity.
5. On large sites with extensive concrete work, washouts should be placed in multiple locations for ease
of use by concrete truck drivers.
On-site Temporary Concrete Washout Facility, Transit Truck Washout Procedures:
1. Temporary concrete washout facilities shall be located a minimum of 50 ft from sensitive areas
including storm drain inlets, open drainage facilities, and watercourses. (See Figures D.2.2.2.A,
D.2.2.2.B and D.2.2.2.C).
2. Concrete washout facilities shall be constructed and maintained in sufficient quantity and size to
contain all liquid and concrete waste generated by washout operations.
3. Washout of concrete trucks shall be performed in designated areas only.
4. Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and
discharged into designated washout area or properly disposed of off-site.
5. Once concrete wastes are washed into the designated area and allowed to harden, the concrete should
be broken up, removed, and disposed of per applicable solid waste regulations. Dispose of hardened
concrete on a regular basis.
6. Temporary Above-Grade Concrete Washout Facility
a. Temporary concrete washout facility (type above grade) should be constructed as shown on the
details below, with a recommended minimum length and minimum width of 10 ft, but with
sufficient quantity and volume to contain all liquid and concrete waste generated by washout
operations.
b. Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of
holes, tears, or other defects that compromise the impermeability of the material.
7. Temporary Below-Grade Concrete Washout Facility
a. Temporary concrete washout facilities (type below grade) should be constructed as shown on the
details below, with a recommended minimum length and minimum width of 10 ft. The quantity
and volume should be sufficient to contain all liquid and concrete waste generated by washout
operations.
b. Lath and flagging should be commercial type.
c. Plastic lining material shall be a minimum of 10 mil polyethylene sheeting and should be free of
holes, tears, or other defects that compromise the impermeability of the material.
d. Liner seams shall be installed in accordance with manufacturers’ recommendations.
e. Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic
lining material.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-77
SECTION D.2.2 SWPPS MEASURES
Maintenance Standards
Inspection and Maintenance
1. Inspect and verify that concrete washout BMPs are in place prior to the commencement of concrete
work.
2. During periods of concrete work, inspect daily to verify continued performance.
a. Check overall condition and performance.
b. Check remaining capacity (% full).
c. If using self-installed washout facilities, verify plastic liners are intact and sidewalls are not
damaged.
d. If using prefabricated containers, check for leaks.
3. Washout facilities shall be maintained to provide adequate holding capacity with a minimum
freeboard of 12 inches.
4. Washout facilities must be cleaned, or new facilities must be constructed and ready for use once the
washout is 75% full.
5. If the washout is nearing capacity, vacuum and dispose of the waste material in an approved manner.
a. Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.
b. Do not use sanitary sewer without local approval.
c. Place a secure, non-collapsing, non-water collecting cover over the concrete washout facility prior
to predicted wet weather to prevent accumulation and overflow of precipitation.
d. Remove and dispose of hardened concrete and return the structure to a functional condition.
Concrete may be reused on-site or hauled away for disposal or recycling.
6. When you remove materials from the self-installed concrete washout, build a new structure; or, if the
previous structure is still intact, inspect for signs of weakening or damage, and make any necessary
repairs. Re-line the structure with new plastic after each cleaning.
Removal of Temporary Concrete Washout Facilities
1. When temporary concrete washout facilities are no longer required for the work, the hardened
concrete, slurries and liquids shall be removed and properly disposed of.
2. Materials used to construct temporary concrete washout facilities shall be removed from the site of the
work and disposed of or recycled.
3. Holes, depressions or other ground disturbance caused by the removal of the temporary concrete
washout facilities shall be backfilled, repaired, and stabilized to prevent erosion.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-78
D.2.2.2 CONCRETE WASHOUT AREA
FIGURE D.2.2.2.A CONCRETE WASHOUT AREA (ABOVE GRADE)
SECTION B-B
NTS
SECTION A-A
NTS
STAPLE DETAIL
NTS
PLAN
NTS
ABOVE GRADE TEMPORARY CONCRETE WASHOUT FACILITY
NTS
CONCRETE WASHOUT SIGN DETAIL
NTS 10 mil PLASTIC
LINING
PLAN
NTS
TYPE "ABOVE GRADE" WITH
WOOD PLANKS
TYPE "ABOVE GRADE" WITH STRAW BALES
10 mil PLASTIC
LINING
16 GAUGE
STEEL WIRE
2"
8"
LAG SCREWS ( 12" )
BLACK LETTERS
6" HEIGHT
PLYWOOD 4' X 2'
PAINTED WHITE
WOOD POST
312" x 312" x 8'3'
3'
STRAW
BALES
(TYP.)
STAKE
(TYP.)
WEDGE LOOSE
STRAW
BETWEEN BALES
SAND OR GRAVEL-FILLED
BAGS IN CORNERS
10' MIN. RECOMMENDED
VARIES
WOOD OR
METAL STAKES
(2 PER BALE)
STRAW BALES (2
BALES HIGH, MAX.)
ORIGINAL GROUND
10 mil PLASTIC
LINING
STAPLES (2 PER BALE)
SAND OR GRAVEL-FILLED
BAGS IN CORNERS
NATIVE MATERIAL
(OPTIONAL)
10 mil
PLASTIC
LINING
WOOD FRAME SECURELY
FASTENED AROUND
ENTIRE PERIMETER WITH
TWO STAKES
TWO-STACKED
2x12 ROUGH
WOOD FRAME
STAKE
(TYP.)
10' MIN. RECOMMENDED
VARIES
NOTES:
1.ACTUAL LAYOUT DETERMINED IN
THE FIELD
2.THE CONCRETE WASHOUT SIGN
SHALL BE INSTALLED WITHIN 30'
OF THE FACILITY
1' MIN.
Adapted from CalTrans Fig4-14 SAC 8-14-02
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-79
SECTION D.2.2 SWPPS MEASURES
FIGURE D.2.2.2.B CONCRETE WASHOUT AREA (BELOW GRADE)
EARTHEN BERM
TYPICAL SECTION
NTS
BELOW GRADE TEMPORARY CONCRETE WASHOUT FACILITY
NTS
CONCRETE WASHOUT SIGN DETAIL
NTS
SANDBAG
PLAN
NTS
Adapted from CalTrans Fig4-14 SAC 8-14-02
10 mil
PLASTIC
LINING
LAG SCREWS ( 12" )
BLACK
LETTERS
6" HEIGHT
PLYWOOD 4' X 2'
PAINTED WHITE
WOOD POST
312" x 312" x 8'3'
3'
EARTHEN
BERM
10 mil
PLASTIC
LINING
SANDBAG
10' MIN. RECOMMENDED
VARIES
BERM
3'
LATH AND
FLAGGING
ON 3 SIDES
NOTES:
1.ACTUAL LAYOUT DETERMINED IN
THE FIELD
2.THE CONCRETE WASHOUT SIGN
SHALL BE INSTALLED WITHIN 30' OF
THE FACILITY
FIGURE D.2.2.2.C PREFABRICATED CONCRETE WASHOUT CONTAINER W/RAMP
4/24/2016 2016 Surface Water Design Manual – Appendix D D-80
D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION
D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION
Purpose
Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high
pH (concrete cutting), both of which can violate the water quality standards in the receiving water.
Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to
minimize and eliminate process water and slurry created through sawcutting or surfacing from entering
waters of the State.
Conditions of Use
Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and
surfacing operations include, but are not limited to, sawing, coring, grinding, roughening, hydro-
demolition, bridge and road surfacing
Design and Installation Specifications
1. Vacuum slurry and cuttings during cutting and surfacing operations.
2. Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.
3. Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including
stormwater systems. This may require temporarily blocking catch basins.
4. Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface
water quality standards.
5. Do not allow process water generated during hydro-demolition, surface roughening or similar
operations to drain to any natural or constructed drainage conveyance including stormwater systems.
Dispose process water in a manner that does not violate ground water or surface water quality
standards.
6. Handle and dispose cleaning waste material and demolition debris in a manner that does not cause
contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate
disposal site.
Maintenance Standards
Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters
of the state. If inspections show that a violation of water quality standards could occur, stop operations and
immediately implement preventive measures such as berms, barriers, secondary containment, and vacuum
trucks.
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SECTION D.2.2 SWPPS MEASURES
D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT
Purpose
Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from
material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a
designated area, and install secondary containment.
Conditions of Use
These procedures are suitable for use at all construction sites with delivery and storage of the following
materials:
• Petroleum products such as fuel, oil and grease
• Soil stabilizers and binders (e.g. Polyacrylamide)
• Fertilizers, pesticides and herbicides
• Detergents
• Asphalt and concrete compounds
• Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds
• Any other material that may be detrimental if released to the environment
Design and Installation Specifications
The following steps should be taken to minimize risk:
1. Temporary storage area should be located away from vehicular traffic, near the construction
entrance(s), and away from waterways or storm drains.
2. Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be
kept in their original labeled containers.
3. Hazardous material storage on-site should be minimized.
4. Hazardous materials should be handled as infrequently as possible.
5. During the wet weather season (Oct 1 – April 30), consider storing materials in a covered area.
6. Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a
children’s wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small
amounts of material may be secondarily contained in “bus boy” trays or concrete mixing trays.
7. Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a
pallet and, when possible, and within secondary containment.
8. If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the
lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums,
preventing water from collecting.
Material Storage Areas and Secondary Containment Practices:
1. Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in
approved containers and drums and shall not be overfilled. Containers and drums shall be stored in
temporary secondary containment facilities.
2. Temporary secondary containment facilities shall provide for a spill containment volume able to
contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the
largest container within its boundary, whichever is greater.
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D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT
3. Secondary containment facilities shall be impervious to the materials stored therein for a minimum
contact time of 72 hours.
4. Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the
event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums.
These liquids shall be handled as hazardous waste unless testing determines them to be non-
hazardous.
5. Sufficient separation should be provided between stored containers to allow for spill cleanup and
emergency response access.
6. During the wet weather season (Oct 1 – April 30), each secondary containment facility shall be
covered during non-working days, prior to and during rain events.
7. Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill
clean-up material (spill kit).
8. The spill kit should include, at a minimum:
• 1-Water Resistant Nylon Bag
• 3-Oil Absorbent Socks 3”x 4’
• 2-Oil Absorbent Socks 3”x 10’
• 12-Oil Absorbent Pads 17”x19”
• 1-Pair Splash Resistant Goggles
• 3-Pair Nitrile Gloves
• 10-Disposable Bags with Ties
• Instructions
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-83
SECTION D.2.2 SWPPS MEASURES
D.2.2.5 CONSTRUCTION STORMWATER CHEMICAL TREATMENT
Purpose
This BMP applies when using stormwater chemicals in batch treatment or flow-through treatment.
Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a construction
site. Sedimentation ponds are effective at removing larger particulate matter by gravity settling, but are
ineffective at removing smaller particulates such as clay and fine silt. Traditional erosion and sediment
control BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in
receiving water.
Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants.
Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when
construction is to proceed through the wet season.
Conditions of Use
Formal written approval from Ecology is required for the use of chemical treatment regardless of
site size. Accordingly, the requirements herein reflect Ecology’s review and approval process, including
references to the Stormwater Management Manual for Western Washington (SMMWW). The Local
Permitting Authority may also require review and approval. When approved, the chemical treatment
systems must be included in the SWPPS portion of the project’s Construction Stormwater Pollution
Prevention plan (CSWPP).
Design and Installation Specifications
(See Appendix II-B in the Stormwater Management Manual for Western Washington for background
information on chemical treatment.)
Criteria for Chemical Treatment Product Use:
Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms.
The Chemical Technology Assessment Protocol (CTAPE) must be used to evaluate chemicals proposed
for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for
stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or
flow-through treatment), allowable application rates, and conditions of use can be found at the Department
of Ecology Emerging Technologies website:
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.html .
Treatment System Design Considerations:
The design and operation of a chemical treatment system should take into consideration the factors that
determine optimum, cost-effective performance. It is important to recognize the following:
• Only Ecology approved chemicals may be used and must follow approved dose rate.
• The pH of the stormwater must be in the proper range for the polymers to be effective, which is
typically 6.5 to 8.5
• The coagulant must be mixed rapidly into the water to ensure proper dispersion.
• A flocculation step is important to increase the rate of settling, to produce the lowest turbidity, and to
keep the dosage rate as low as possible.
• Too little energy input into the water during the flocculation phase results in flocs that are too small
and/or insufficiently dense. Too much energy can rapidly destroy floc as it is formed.
• Care must be taken in the design of the withdrawal system to minimize outflow velocities and to
prevent floc discharge. Discharge from a batch treatment system should be directed through a physical
4/24/2016 2016 Surface Water Design Manual – Appendix D D-84
D.2.2.5 CONSTRUCTION STORMWATER CHEMICAL TREATMENT
filter such as a vegetated swale that would catch any unintended floc discharge. Currently, flow-
through systems always discharge through the chemically enhanced sand filtration system.
• System discharge rates must take into account downstream conveyance integrity.
Polymer Batch Treatment Process Description:
A batch chemical treatment system consists of the stormwater collection system (either temporary
diversion or the permanent site drainage system), a storage pond, pumps, a chemical feed system,
treatment cells, and interconnecting piping.
The batch treatment system shall use a minimum of two lined treatment cells in addition to an untreated
stormwater storage pond. Multiple treatment cells allow for clarification of treated water while other cells
are being filled or emptied. Treatment cells may be ponds or tanks. Ponds with constructed earthen
embankments greater than six feet high or which impound more than 10 acre-feet require special
engineering analyses. The Ecology Dam Safety Section has specific design criteria for dams in
Washington State (see http://www.ecy.wa.gov/programs/wr/dams/GuidanceDocs.html ).
Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an
untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored
until treatment occurs. It is important that the holding pond be large enough to provide adequate storage.
The first step in the treatment sequence is to check the pH of the stormwater in the untreated stormwater
storage pond. The pH is adjusted by the application of carbon dioxide or a base until the stormwater in the
storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon dioxide is added immediately
downstream of the transfer pump. Typically sodium bicarbonate (baking soda) is used as a base, although
other bases may be used. When needed, base is added directly to the untreated stormwater storage pond.
The stormwater is recirculated with the treatment pump to provide mixing in the storage pond. Initial pH
adjustments should be based on daily bench tests. Further pH adjustments can be made at any point in the
process.
Once the stormwater is within the desired pH range (dependent on polymer being used), the stormwater is
pumped from the untreated stormwater storage pond to a treatment cell as polymer is added. The polymer
is added upstream of the pump to facilitate rapid mixing.
After polymer addition, the water is kept in a lined treatment cell for clarification of the sediment-floc. In a
batch mode process, clarification typically takes from 30 minutes to several hours. Prior to discharge
samples are withdrawn for analysis of pH, flocculent chemical concentration, and turbidity. If both are
acceptable, the treated water is discharged.
Several configurations have been developed to withdraw treated water from the treatment cell. The
original configuration is a device that withdraws the treated water from just beneath the water surface
using a float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the
possibility of picking up sediment-floc from the bottom of the pond. The struts are usually set at a
minimum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the
cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and
down with the water level. More recent designs have an H-shaped array of pipes, set on the horizontal.
This scheme provides for withdrawal from four points rather than one. This configuration reduces the
likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vortex to form. Inlet
diffusers, a long floating or fixed pipe with many small holes in it, are also an option.
Safety is a primary concern. Design should consider the hazards associated with operations, such as
sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should
have life rings, ladders, or steps extending from the bottom to the top.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-85
SECTION D.2.2 SWPPS MEASURES
Polymer Flow-Through Treatment Process Description:
At a minimum, a flow-through chemical treatment system consists of the stormwater collection system
(either temporary diversion or the permanent site drainage system), an untreated stormwater storage pond,
and the chemically enhanced sand filtration system.
Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an
untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored
until treatment occurs. It is important that the holding pond be large enough to provide adequate storage.
Stormwater is then pumped from the untreated stormwater storage pond to the chemically enhanced sand
filtration system where polymer is added. Adjustments to pH may be necessary before chemical addition.
The sand filtration system continually monitors the stormwater for turbidity and pH. If the discharge water
is ever out of an acceptable range for turbidity or pH, the water is recycled to the untreated stormwater
pond where it can be retreated.
For batch treatment and flow-through treatment, the following equipment should be located in a lockable
shed:
• The chemical injector.
• Secondary containment for acid, caustic, buffering compound, and treatment chemical.
• Emergency shower and eyewash.
• Monitoring equipment which consists of a pH meter and a turbidimeter.
System Sizing:
Certain sites are required to implement flow control for the developed sites. These sites must also control
stormwater release rates during construction. Generally, these are sites that discharge stormwater directly,
or indirectly, through a conveyance system, into a fresh water. System sizing is dependent on flow control
requirements.
Sizing Criteria for Batch Treatment Systems for Flow Control Exempt Water Bodies:
The total volume of the untreated stormwater storage pond and treatment ponds or tanks must be large
enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a
minimum the untreated stormwater storage pond be sized to hold 1.5 times the runoff volume of the 10-
year, 24-hour storm event. Bypass should be provided around the chemical treatment system to
accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in
Volume 3, Chapter 2 of the SWMMWW. Worst-case land cover conditions (i.e., producing the most runoff)
should be used for analyses (in most cases, this would be the land cover conditions just prior to final
landscaping).
Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with access for
maintenance may be beneficial.
There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a larger
volume of water each time a batch is processed. However, the larger the cell the longer the time required
to empty the cell. A larger cell may also be less effective at flocculation and therefore require a longer
settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow
rate times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work
period, given 1 hour of flocculation followed by two hours of settling.
If the discharge is directly to a flow control exempt receiving water listed in Appendix I-E of Volume I of
the SWMMWW, or to an infiltration system, there is no discharge flow limit.
Ponds sized for flow control water bodies must at a minimum meet the sizing criteria for flow control
exempt waters.
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D.2.2.5 CONSTRUCTION STORMWATER CHEMICAL TREATMENT
Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies:
When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies, the
treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be
sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system
flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the treatment system
flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic loading rates
may be more appropriate for other systems. Bypass should be provided around the chemical treatment
system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in
Volume 3, Chapter 2 of the SWMMWW. Worst-case land cover conditions (i.e., producing the most runoff)
should be used for analyses (in most cases, this would be the land cover conditions just prior to final
landscaping).
Sizing Criteria for Flow Control Water Bodies:
Sites that must implement flow control for the developed site condition must also control stormwater
release rates during construction. Construction site stormwater discharges shall not exceed the discharge
durations of the pre-developed condition for the range of pre-developed discharge rates from ½ of the 2-
year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-
developed condition to be matched shall be the land cover condition immediately prior to the development
project. This restriction on release rates can affect the size of the storage pond and treatment cells.
The following is how WWHM can be used to determine the release rates from the chemical treatment
systems:
1. Determine the pre-developed flow durations to be matched by entering the existing land use area
under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow
through the 10-year flow.
2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM.
3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario.
4. While in the “Developed Mitigated” scenario, add a pond element under the basin element containing
the post-developed land use areas. This pond element represents information on the available
untreated stormwater storage and discharge from the chemical treatment system. In cases where the
discharge from the chemical treatment system is controlled by a pump, a stage/storage/discharge
(SSD) table representing the pond must be generated outside WWHM and imported into WWHM.
WWHM can route the runoff from the post-developed condition through this SSD table (the pond)
and determine compliance with the flow duration standard. This would be an iterative design
procedure where if the initial SSD table proved to be inadequate, the designer would have to modify
the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The
iteration will continue until a pond that complies with the flow duration standard is correctly sized.
Notes on SSD table characteristics:
• The pump discharge rate would likely be initially set at just below ½ of the 2-year flow from the
pre-developed condition. As runoff coming into the untreated stormwater storage pond increases
and the available untreated stormwater storage volume gets used up, it would be necessary to
increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year
must be such that they provide some relief to the untreated stormwater storage needs but at the
same time will not cause violations of the flow duration standard at the higher flows. The final
design SSD table will identify the appropriate pumping rates and the corresponding stage and
storages.
• When building such a flow control system, the design must ensure that any automatic adjustments
to the pumping rates will be as a result of changes to the available storage in accordance with the
final design SSD table.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-87
SECTION D.2.2 SWPPS MEASURES
5. It should be noted that the above procedures would be used to meet the flow control requirements. The
chemical treatment system must be able to meet the runoff treatment requirements. It is likely that the
discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that
is the case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be
reduced to allow proper treatment. Any reduction in the flows would likely result in the need for a
larger untreated stormwater storage volume.
If the discharge is to a municipal storm drainage system, the allowable discharge rate may be limited by
the capacity of the public system. It may be necessary to clean the municipal storm drainage system prior
to the start of the discharge to prevent scouring solids from the drainage system. If the municipal storm
drainage system discharges to a water body not on the flow control exempt list, the project site is subject to
flow control requirements. Obtain permission from the owner of the collection system before discharging
to it.
If system design does not allow you to discharge at the slower rates as described above and if the site has a
retention or detention pond that will serve the planned development, the discharge from the treatment
system may be directed to the permanent retention/detention pond to comply with the flow control
requirement. In this case, the untreated stormwater storage pond and treatment system will be sized
according to the sizing criteria for flow-through treatment systems for flow control exempt water bodies
described earlier except all discharge (water passing through the treatment system and stormwater
bypassing the treatment system) will be directed into the permanent retention/detention pond. If site
constraints make locating the untreated stormwater storage pond difficult, the permanent
retention/detention pond may be divided to serve as the untreated stormwater storage pond and the post-
treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not
mix with the treated water. Both untreated stormwater storage requirements, and adequate post-treatment
flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered
into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement.
Maintenance Standards
Monitoring:
At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily log
kept on site. Additional testing may be required by the NPDES permit based on site conditions.
Operational Monitoring:
• Total volume treated and discharged.
• Flow must be continuously monitored and recorded at not greater than 15-minute intervals.
• Type and amount of chemical used for pH adjustment.
• Amount of polymer used for treatment.
• Settling time.
Compliance Monitoring:
Influent and effluent pH, flocculent chemical concentration, and turbidity must be continuously monitored
and recorded at not greater than 15-minute intervals. pH and turbidity of the receiving water.
Biomonitoring:
Treated stormwater must be non-toxic to aquatic organisms. Treated stormwater must be tested for aquatic
toxicity or residual chemicals. Frequency of biomonitoring will be determined by Ecology.
Residual chemical tests must be approved by Ecology prior to their use.
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D.2.2.5 CONSTRUCTION STORMWATER CHEMICAL TREATMENT
If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity. Bioassays shall
be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. Acute
toxicity tests shall be conducted per the CTAPE protocol.
Discharge Compliance:
Prior to discharge, treated stormwater must be sampled and tested for compliance with pH,
flocculent chemical concentration, and turbidity limits. These limits may be established by the
Construction Stormwater General Permit or a site-specific discharge permit. Sampling and testing for
other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 standard
units and not cause a change in the pH of the receiving water of more than 0.2 standard units. Treated
stormwater samples and measurements shall be taken from the discharge pipe or another location
representative of the nature of the treated stormwater discharge. Samples used for determining compliance
with the water quality standards in the receiving water shall not be taken from the treatment pond prior to
decanting. Compliance with the water quality standards is determined in the receiving water.
Operator Training:
Each contractor who intends to use chemical treatment shall be trained by an experienced contractor.
Each site using chemical treatment must have an operator trained and certified by an organization
approved by Ecology.
Standard BMPs:
Surface stabilization BMPs should be implemented on site to prevent significant erosion. All sites shall
use a truck wheel wash to prevent tracking of sediment off site.
Sediment Removal and Disposal:
• Sediment shall be removed from the storage or treatment cells as necessary. Typically, sediment
removal is required at least once during a wet season and at the decommissioning of the cells.
Sediment remaining in the cells between batches may enhance the settling process and reduce the
required chemical dosage.
• Sediment that is known to be non-toxic may be incorporated into the site away from drainages.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-89
SECTION D.2.2 SWPPS MEASURES
D.2.2.6 CONSTRUCTION STORMWATER FILTRATION
Purpose
Filtration removes sediment from runoff originating from disturbed areas of the site.
Background Information:
Filtration with sand media has been used for over a century to treat water and wastewater. The use of sand
filtration for treatment of stormwater has developed recently, generally to treat runoff from streets, parking
lots, and residential areas. The application of filtration to construction stormwater treatment is currently
under development.
Conditions of Use
Traditional BMPs used to control soil erosion and sediment loss from sites under development may not be
adequate to ensure compliance with the water quality standard for turbidity in the receiving water.
Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5
μm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the
stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water
quality standard for turbidity.
The use of construction stormwater filtration does not require approval from Ecology as long as treatment
chemicals are not used. Filtration in conjunction with polymer treatment requires testing under the
Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be initiated. Approval from
the appropriate regional Ecology office must be obtained at each site where polymers use is proposed prior
to use. For more guidance on stormwater chemical treatment see BMP D.2.2.5.
Design and Installation Specifications
Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow.
Rapid sand filters are the typical system used for water and wastewater treatment. They can achieve
relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have automatic backwash
systems to remove accumulated solids. In contrast, slow sand filters have very low hydraulic rates, on the
order of 0.02 gpm/sf, because they do not have backwash systems. Slow sand filtration has generally been
used to treat stormwater. Slow sand filtration is mechanically simple in comparison to rapid sand filtration
but requires a much larger filter area.
Filtration Equipment.
Sand media filters are available with automatic backwashing features that can filter to 50 μm particle size.
Screen or bag filters can filter down to 5 μm. Fiber wound filters can remove particles down to 0.5 μm.
Filters should be sequenced from the largest to the smallest pore opening. Sediment removal efficiency
will be related to particle size distribution in the stormwater.
Treatment Process Description.
Stormwater is collected at interception point(s) on the site and is diverted to an untreated stormwater
sediment pond or tank for removal of large sediment and storage of the stormwater before it is treated by
the filtration system. The untreated stormwater is pumped from the trap, pond, or tank through the
filtration system in a rapid sand filtration system. Slow sand filtration systems are designed as flow
through systems using gravity.
Maintenance Standards
Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure drop
across the filter. If the backwash water volume is not large or substantially more turbid than the untreated
stormwater stored in the holding pond or tank, backwash return to the untreated stormwater pond or tank
may be appropriate. However, other means of treatment and disposal may be necessary.
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D.2.2.6 CONSTRUCTION STORMWATER FILTRATION
• Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged.
• Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically, sediment
removal is required once or twice during a wet season and at the decommissioning of the ponds.
Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies:
When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies the
treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be
sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system
flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the treatment system
flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic loading rates
may be more appropriate for other systems. Bypass should be provided around the chemical treatment
system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in
Volume 3, Chapter 2 of the SWMMWW (or Chapter 4 of the King County Surface Water Design Manual if
no chemicals are proposed for use). Worst-case conditions (i.e., producing the most runoff) should be used
for analyses (most likely conditions present prior to final landscaping).
Sizing Criteria for Flow Control Water Bodies:
Sites that must implement flow control for the developed site condition must also control stormwater
release rates during construction. Construction site stormwater discharges shall not exceed the discharge
durations of the pre-developed condition for the range of pre-developed discharge rates from 1/2 of the 2-
year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-
developed condition to be matched shall be the land cover condition immediately prior to the development
project. This restriction on release rates can affect the size of the storage pond, the filtration system, and
the flow rate through the filter system.
The following is how WWHM can be used to determine the release rates from the filtration systems:
1. Determine the pre-developed flow durations to be matched by entering the land use area under the
“Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the
10-year flow.
2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM.
3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario.
4. There are two possible ways to model stormwater filtration systems:
a. The stormwater filtration system uses an untreated stormwater storage pond/tank and the
discharge from this pond/tank is pumped to one or more filters. In-line filtration chemicals would
be added to the flow right after the pond/tank and before the filter(s). Because the discharge is
pumped, WWHM can’t generate a stage/storage /discharge (SSD) table for this system. This
system is modeled the same way as described Ecology’s BMP C250 (or BMP D.2.2.5 when
seeking King County approval for non-chemical treatment) and is as follows:
While in the “Developed Mitigated” scenario, add a pond element under the basin element
containing the post-developed land use areas. This pond element represents information on the
available untreated stormwater storage and discharge from the filtration system. In cases where
the discharge from the filtration system is controlled by a pump, a stage/storage/discharge (SSD)
table representing the pond must be generated outside WWHM and imported into WWHM.
WWHM can route the runoff from the post-developed condition through this SSD table (the
pond) and determine compliance with the flow duration standard. This would be an iterative
design procedure where if the initial SSD table proved to be out of compliance, the designer
would have to modify the SSD table outside WWHM and re-import in WWHM and route the
runoff through it again. The iteration will continue until a pond that enables compliance with the
flow duration standard is designed.
Notes on SSD table characteristics:
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-91
SECTION D.2.2 SWPPS MEASURES
• The pump discharge rate would likely be initially set at just below ½ if the 2-year flow from
the pre-developed condition. As runoff coming into the untreated stormwater storage pond
increases and the available untreated stormwater storage volume gets used up, it would be
necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½
of the 2-year must be such that they provide some relief to the untreated stormwater storage
needs but at the same time they will not cause violations of the flow duration standard at the
higher flows. The final design SSD table will identify the appropriate pumping rates and the
corresponding stage and storages.
• When building such a flow control system, the design must ensure that any automatic
adjustments to the pumping rates will be as a result of changes to the available storage in
accordance with the final design SSD table.
b. The stormwater filtration system uses a storage pond/tank and the discharge from this pond/tank
gravity flows to the filter. This is usually a slow sand filter system and it is possible to model it in
WWHM as a Filter element or as a combination of Pond and Filter element placed in series. The
stage/storage/discharge table(s) may then be generated within WWHM as follows:
i. While in the “Developed Mitigated” scenario, add a Filter element under the basin element
containing the post-developed land use areas. The length and width of this filter element
would have to be the same as the bottom length and width of the upstream untreated
stormwater storage pond/tank.
ii. In cases where the length and width of the filter is not the same as those for the bottom of the
upstream untreated stormwater storage tank/pond, the treatment system may be modeled as a
Pond element followed by a Filter element. By having these two elements, WWHM would
then generate a SSD table for the storage pond which then gravity flows to the Filter element.
The Filter element downstream of the untreated stormwater storage pond would have a
storage component through the media, and an overflow component for when the filtration
capacity is exceeded.
WWHM can route the runoff from the post-developed condition through the treatment systems in
4b and determine compliance with the flow duration standard. This would be an iterative design
procedure where if the initial sizing estimates for the treatment system proved to be inadequate,
the designer would have to modify the system and route the runoff through it again. The iteration
would continue until compliance with the flow duration standard is achieved.
5. It should be noted that the above procedures would be used to meet the flow control requirements. The
filtration system must be able to meet the runoff treatment requirements. It is likely that the discharge
flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the
case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be reduced
to allow proper treatment. Any reduction in the flows would likely result in the need for a larger
untreated stormwater storage volume.
If system design does not allow you to discharge at the slower rates as described above and if the site has a
retention or detention pond that will serve the planned development, the discharge from the treatment
system may be directed to the permanent retention/detention pond to comply with the flow control
requirements. In this case, the untreated stormwater storage pond and treatment system will be sized
according to the sizing criteria for flow-through treatment systems for flow control exempt waterbodies
described earlier except all discharges (water passing through the treatment system and stormwater
bypassing the treatment system) will be directed into the permanent retention/detention pond. If site
constraints make locating the untreated stormwater storage pond difficult, the permanent
retention/detention pond may be divided to serve as the untreated stormwater discharge pond and the post-
treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not
mix with the treated water. Both untreated stormwater storage requirements, and adequate post-treatment
flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered
into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-92
D.2.2.7 High pH NEUTRALIZATION USING CO2
D.2.2.7 HIGH pH NEUTRALIZATION USING CO2
Purpose
When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range
of 6.5 to 8.5, this process is called pH neutralization. pH neutralization involves the use of solid or
compressed carbon dioxide gas in water requiring neutralization. Neutralized stormwater may be
discharged to surface waters under the General Construction NPDES permit.
Neutralized process water such as concrete truck wash-out, hydro-demolition, or saw-cutting slurry must
be managed to prevent discharge to surface waters. Any stormwater contaminated during concrete work is
considered process wastewater and must not be discharged to surface waters.
Reason for pH Neutralization:
A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this neutral pH is required for
the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic
organisms may become stressed and may die.
Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH
conditions. A high level of calcium hardness in waters of the state is not allowed.
The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Ground water standard
for calcium and other dissolved solids in Washington State is less than 500 mg/l.
Conditions of Use
Causes of High pH:
High pH at construction sites is most commonly caused by the contact of stormwater with poured or
recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials.
(See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures). The
principal caustic agent in cement is calcium hydroxide (free lime).
Advantages of CO2 Sparging:
• Rapidly neutralizes high pH water.
• Cost effective and safer to handle than acid compounds.
• CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels.
• Material is readily available.
The Chemical Process:
When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can further
dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reaction as
well. The colder the water temperature is the slower the reaction occurs and the warmer the water
temperature is the quicker the reaction occurs. Most construction applications in Washington State have
water temperatures in the 50°F or higher range so the reaction is almost simultaneous.
Design and Installation Specifications
Treatment Process:
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-93
SECTION D.2.2 SWPPS MEASURES
High pH water may be treated using continuous treatment, continuous discharge systems. These
manufactured systems continuously monitor influent and effluent pH to ensure that pH values are within
an acceptable range before being discharged. All systems must have fail safe automatic shut off switches
in the event that pH is not within the acceptable discharge range. Only trained operators may operate
manufactured systems. System manufacturers often provide trained operators or training on their devices.
The following procedure may be used when not using a continuous discharge system:
1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the regulations
set by the jurisdiction.
2. Every effort should be made to isolate the potential high pH water in order to treat it separately from
other stormwater on-site.
3. Water should be stored in an acceptable storage facility, detention pond, or containment cell prior to
treatment.
4. Transfer water to be treated to the treatment structure. Ensure that treatment structure size is sufficient
to hold the amount of water that is to be treated. Do not fill tank completely, allow at least 2 feet of
freeboard.
5. The operator samples the water for pH and notes the clarity of the water. As a rule of thumb, less CO2
is necessary for clearer water. This information should be recorded.
6. In the pH adjustment structure, add CO2 until the pH falls in the range of 6.9-7.1. Remember that pH
water quality standards apply so adjusting pH to within 0.2 pH units of receiving water (background
pH) is recommended. It is unlikely that pH can be adjusted to within 0.2 pH units using dry ice.
Compressed carbon dioxide gas should be introduced to the water using a carbon dioxide diffuser
located near the bottom of the tank, this will allow carbon dioxide to bubble up through the water and
diffuse more evenly.
7. Slowly discharge the water making sure water does not get stirred up in the process. Release about
80% of the water from the structure leaving any sludge behind.
8. Discharge treated water through a pond or drainage system.
9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of water are
undergoing pH treatment, sludge can be left in treatment structure for the next batch treatment.
Dispose of sludge when it fills 50% of tank volume.
Sites that must implement flow control for the developed site must also control stormwater release rates
during construction. All treated stormwater must go through a flow control facility before being released
to surface waters which require flow control.
Maintenance Standards
Safety and Materials Handling:
• All equipment should be handled in accordance with OSHA rules and regulations.
• Follow manufacturer guidelines for materials handling.
Operator Records:
Each operator should provide:
• A diagram of the monitoring and treatment equipment.
• A description of the pumping rates and capacity the treatment equipment is capable of treating.
Each operator should keep a written record of the following:
4/24/2016 2016 Surface Water Design Manual – Appendix D D-94
D.2.2.7 High pH NEUTRALIZATION USING CO2
• Client name and phone number.
• Date of treatment.
• Weather conditions.
• Project name and location.
• Volume of water treated.
• pH of untreated water.
• Amount of CO2 needed to adjust water to a pH range of 6.9-7.1.
• pH of treated water.
• Discharge point location and description.
A copy of this record should be given to the client/contractor who should retain the record for three years.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-95
SECTION D.2.2 SWPPS MEASURES
D.2.2.8 pH CONTROL FOR HIGH pH WATER
Purpose
When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range
of 6.5 to 8.5, this process is called pH neutralization. Stormwater with pH levels exceeding water quality
standards may be treated by infiltration, dispersion in vegetation or compost, pumping to a sanitary sewer,
disposal at a permitted concrete batch plant with pH neutralization capabilities, or carbon dioxide
sparging. BMP D.2.2.7, High pH Neutralization Using CO2 gives guidelines for carbon dioxide sparging.
Reason for pH Neutralization:
A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this pH range is required for
the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic
organisms may become stressed and may die.
Conditions of Use
Causes of High pH:
High pH levels at construction sites are most commonly caused by the contact of stormwater with poured
or recycled concrete, cement, mortars, and other Portland cement or lime containing construction
materials. (See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures).
The principal caustic agent in cement is calcium hydroxide (free lime).
Design and Installation Specifications
Disposal Methods:
Infiltration
• Infiltration is only allowed if soil type allows all water to infiltrate (no surface runoff) without causing
or contributing to a violation of surface or ground water quality standards.
• Infiltration techniques should be consistent with Chapter 5 of the King County Surface Water Design
Manual
Dispersion
• Dispersion techniques should be consistent with Chapter 5 and Appendix C of the King County
Surface Water Design Manual
Sanitary Sewer Disposal
• Local sewer authority approval is required prior to disposal via the sanitary sewer.
Concrete Batch Plant Disposal
• Only permitted facilities may accept high pH water.
• Facility should be contacted before treatment to ensure they can accept the high pH water.
Stormwater Discharge
Any pH treatment options that generate treated water that must be discharged off site are subject to flow
control requirements. Sites that must implement flow control for the developed site must also control
stormwater release rates during construction. All treated stormwater must go through a flow control
facility before being released to surface waters which require flow control.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-96
D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
The use of soil amendments (including cement treated base (CTB) and cement kiln dust (CKD)) on
development sites must be approved by King County. The approval process is described in "Processing
Requirements for Use of Soil Amendments on Construction Sites" below.
Use of Soil Amendments
It is sometimes a construction practice to add soil amendments to the surfaces of some construction areas
in order to stabilize the ground for building. This practice includes placing an additive on the ground then
mixing with the soil to a specified depth and finally compacting the mix. When mixed with the soil, the
moisture in the ground may allow these additives to create a chemical reaction that cures similar to
concrete and may absorb excessive moisture to allow soils to be compacted. The end result is a stable site
for constructing a road or building pad.
Because soil amendments may be rich in lime content and other material, water runoff from these areas
can be affected. If not controlled and treated, this could result in a degradation of water quality and natural
drainage systems. Because these additives come in a fine powder form, the actual application can create
fugitive dust. When mixed with water, some additives can become corrosive.
Definitions
The following are definitions of soil amendment products that are allowed for use under these procedures:
1. Cement Kiln Dust (CKD) is a by-product in the manufacturing of cement9.
2. Cement Treated Base (CTB) utilizes Portland Cement Type II as the soil additive.
CTB/CKD Soil Amendment BMPs
Table D.2.2.9.A on the following pages lists twelve BMP categories of action and specific BMPs for each
category to be applied when proposing CTB/CKD soil amendments or using soil amendments onsite.
Note: Additional BMPs may be required to prevent adverse impacts to the public and/or the environment.
It is the responsibility of the permit holder to remain in compliance with all other applicable local, state,
and federal regulations.
9 CKD is collected by air pollution control devices used to clean kiln exhaust during the manufacturing of Portland Cement. EPA
has classified CKD a non-hazardous waste product provided management standards are followed for groundwater protection
and control of fugitive dust releases.
CKD should not to be confused with Fly Ash, which is a by-product of burning coal or wood and incineration of other material.
Fly ash can contain major oxides and trace metals, depending upon the fuel source, and is considered too hazardous for use
as a soil amendment. Using this product is not authorized or endorsed by Ecology or King County.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-97
SECTION D.2.2 SWPPS MEASURES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
1. Materials
Source
Analysis
Solubility
Testing &
Specifications
A. If CKD is proposed, a chemical analysis of soluble pollutants
of the product to be used will be provided to the Washington
State Department of Ecology (Ecology) and the King County
Department of Permitting and Environmental Review (DPER)
in advance of any product is applied.
B. CTB/CKD mixing percentage is anticipated to be
approximately 3 percent to 5 percent.
C. A Geotechnical Engineer will establish the mixing percentage
for the on-site soils.
D. All treatment procedures shall be directed, monitored, and
verified by a Geotechnical Engineer.
E. Soil amendments will never occur in excess of the ability of
the on-site equipment and resources to meet all BMP
requirements specified herein.
2. Site
Preparation
Runoff
Collection
System
A. Areas that are to be treated as shown on the plan are flagged
off to prevent equipment from leaving treated area and going
onto untreated areas, and to prevent unauthorized equipment
from entering the treated area.
B. Assessment of surface runoff collection points are noted.
C. Cutoff trenches, collection sumps, and pumps are installed.
D. Sealed storage tanks will be properly sized to contain all
runoff from treated areas.
E. Sealed storage tanks shall be set up and ready for use to treat
contact water.
F. An approved wheel wash will be constructed at the
construction exit, typically a paved ramp sump that utilizes
high-pressure washers.
G. Copies of Treatment Plan, Approval, and Contingency Plan
area are required to be located on site.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-98
D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
3. Lay-down
Mixing
Equipment
A. Exposure of CTB/CKD materials to air to be minimized.
Delivery tankers shall be set up to place CTB/CKD directly
into spreading trucks or equipment.
B. CTB/CKD operations are only allowed during daylight hours.
C. Tarps or dust bags will be used over the discharge truck hose
at unloading to prevent dust particles for becoming airborne.
D. Unloading will occur at the lowest possible pump pressure.
E. Unloading and mixing will be avoided on high wind days.
PSAPCA Section 9.15 prohibits visible emissions of fugitive
dust.
F. CTB/CKD to be placed on ground by large wheeled spreaders
designed for this purpose capable of measuring application.
G. When spreading CTB/CKD it shall be kept 2-3 feet away from
untreated areas boundaries to prevent the material from
migration and contaminating outside the treatment zone.
H. Treatment area will be kept damp/wet at all times CTB/CKD
is being spread and mixed. Skirting around applicator/spreader
and mixer is required to minimize CTB/CKD dust.
I. CTB/CKD is to be roto-tilled into soil immediately after being
spread onto soils and shall be done with a skirted tiller.
J. Direct auguring machine that measures, spreads, and mixes
CTB/CKD in one operation is preferred.
K. Compaction will be complete within 2 hours after CTB/CKD
application.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-99
SECTION D.2.2 SWPPS MEASURES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
4. Site
Management
Work Progress
and Weather
Conditions
A. Dust suppression by use of water trucks shall be used on areas
where work on dry soil is performed and potential airborne
contamination may occur.
B. The volume of CTB/CKD allowed on site will be limited to
the amount that can be used within a normal workday. Every
effort will be made to forecast the daily delivery rate to match
the daily on-site use rate.
C. CTB/CKD will not be added to soils at a rate that exceeds the
ability of on-site resources to immediately commence mixing
and compacting.
D. No work will occur in rain heavier than drizzle, or under
drizzle that exceeds 6 hours duration, or under any rainfall
which generates runoff from the areas being worked.
E. Should the weather change to stop the application, remaining
CTB/CKD will be covered and contained to prevent
stormwater from entering storage containment, and causing
runoff.
F. All vehicles and equipment leaving the treatment area/site
must be cleaned/washed to prevent CTB/CKD from leaving
site. Wash water will be contained and treated as needed.
G. CTB/CKD contact water in the wheel wash will be removed
from the site via a vactor truck for transport to an approved
off-site treatment or disposal facility in accordance with all
federal, state, and local laws and regulations; or, if permitted,
to the sanitary sewer system.
5. Surface Water
Collection
A. Surface runoff from the treated areas is to be collected and
stored in onsite sealed treatment tanks.
B. A rigid schedule of TESC inspection, maintenance, and
drainage controls will be maintained.
C. Temporarily plugging and using detention facilities is not
allowed as a storage practice.
D. Runoff from compacted areas amended with CTB/CKD will
be directed to previously sealed tank(s) until pH levels of
water are verified to be within acceptable background water
limits. No uncontrolled discharge or infiltration from the
sealed tank(s) will be allowed.
E. Drainage from areas amended with CTB/CKD within the past
72 hours will be prevented from co-mingling with any other
project drainage.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-100
D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
6. Discharge
Compliance
Applicable
Regulations
A. Any and all discharges from this site will be in compliance
with all applicable federal, state, and local laws and
regulations pertaining to health and safety, water, air, waste,
and wildlife, including the Federal Clean Water Act, Clean Air
Act, and Endangered Species Act. Laboratory analysis of
water is required prior to discharge to verify compliance.
B. No infiltration is allowed to occur if pH readings are above 8.5
standard pH units, or below 6.5 standard pH units.
C. A pH meter must be used to determine levels. pH meter is to
be calibrated following proper QA/QC procedures. Fresh
buffers are to be available to re-calibrate as needed.
D. A log of turbidity and pH readings will be kept on site for
inspection.
E. All treatment of water must be directed, bench tested,
monitored and verified by a qualified water quality specialist.
F. Treated area water runoff shall not enter the permanent
stormwater system.
G. Stormwater drainage system within treatment area is to be
cleaned out prior to use for regular water runoff conveyance
from untreated areas. Water from cleanout is to be tested and
treated following the approved treatment criteria.
7. Natural
Treatment and
Discharge
A. The preferred method of disposal of the treatment water will
be discharge to the sanitary sewer, provided a permit is
obtained to do so.
B. If infiltration is proposed, the area of infiltration is to be
identified, capacity confirmed, and a contingency discharge
plan in place in the event facilities fail to infiltrate.
C. For infiltration, pH limits shall be strictly adhered to.
D. If a permit to discharge to the sanitary sewer is not obtained, a
National Pollutant Discharge Elimination System (NPDES)
discharge permit is required from Ecology. The retention
volume of the lined pond(s) will also be increased to ensure
complete control of the retained volume. Monitoring, bench
testing, and controlled discharge rates, with prior approval by
Ecology, would be needed prior to discharge to an approved
off-site surface drainage system. Sites that currently have
NPDES permits will need to amend permit prior to discharge
to cover this action. County approval is still required.
E. Per KCC 9.12, discharges into receiving drainage systems
shall not have acid or basic pH levels.
F. Sealed storage tanks shall be used to reduce turbidity and pH
before discharge.
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-101
SECTION D.2.2 SWPPS MEASURES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
8. Chemical
Treatment
A. Carbon dioxide sparging (dry ice pellets) may be used as the
chemical treatment agent to reduce the water pH.
B. Any means of water treatment to reduce pH will require an
NPDES discharge permit from Ecology. Permit would only be
granted after bench testing performed by an independent
qualified party.
C. Active mixing will cease if the residual retention water volume
falls below the ability to treat and properly dispose of contact
storm water.
D. Discharge would only occur after the approval of Ecology,
following bench testing and consultation with Ecology.
E. All materials for chemical treatment will be on site and
property stored, during all phases of CTB/CKD treatment.
9. Water
Quality
Monitoring
A. Turbidity and pH will be monitored on a twice-daily basis,
prior to operations and immediately upon ceasing operations,
and these measurements will be recorded. Monitoring will also
occur immediately after any storm event of ½ inch in 24 hours,
or water migration to the retention pond(s), and the
measurements recorded. If the pH approaches 8.0, monitoring
frequency will increase.
B. Turbidity and pH monitoring will occur in all treatment
facilities, stormwater detention facilities, infiltration areas (if
infiltration is used), and in all surface water areas adjacent to
site where stormwater potentially discharges. Additional
upstream surface water sites will be established to determine
background levels of turbidity and pH.
C. All water quality monitoring data will be conducted and
evaluated by an independent, qualified party and conducted
using professionally supportable test protocols and QA/QC
procedures.
10. Reporting
Ecology and
DPER
A. All water quality monitoring data will be included in weekly
DPER TESC reports to DPER, and in weekly NPDES reports
to Ecology.
B. All work, testing, and monitoring associated with the
application of CTB/CKD shall be observed by engineer. The
engineer shall prepare and submit a report to the assigned
DPER project inspector indicating BMPs were/were not being
met.
C. Copies of all reports and logs will be available on site during
the soil and surface runoff treatment activities.
4/24/2016 2016 Surface Water Design Manual – Appendix D D-102
D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
TABLE D.2.2.9.A CTB/CKD Soil Amendment BMPs
Category of
Action Specific Action CTB/CKD Best Management Practices
Other elements to consider:
. Water Quality –
Soils
Source Controls
A. There may be very small amounts of concrete washout
produced onsite as a result of construction of erosion control
measures during reclamation. Concrete washout, if any, would
be retained in a lined enclosure of at least 6-ml visqueen or
plastic sheeting, with no outlet. The washout retention
enclosure would be isolated and separate from any CTB/CKD
area runoff. Contents of the lined concrete washout enclosure
will be removed from the site via a vactor truck for disposal in
an approved off-site treatment or disposal facility in
accordance with all federal, state, and local laws and
regulations. Signed trip tickets, as proof of proper disposal,
will be provided to Ecology and DPER.
. Water Quality –
pH
Cover Measures
A. Areas amended with CTB/CKD for compaction after
CTB/CKD addition will be covered with plastic or visqueen
sheeting, or other impervious material by the end of each
working day.
B. Temporary cover will be maintained over all compacted areas
amended with CTB/CKD until testing confirms that pH levels
are stabilized to background measurements. [Note: Curing to
avoid pH effects has no relationship to the rate at which
material can be compacted in multiple lifts. Compaction will
commence immediately after application and mixing, and
multiple lifts will occur as quickly as each lift is compacted
and ready to accept the next.]
C. Should weather conditions prevent mixing, any unmixed
CTB/CKD remaining on site will be enclosed in a sealed
containment, such as portable silo, or removed from site.
Processing Requirements for Use of High pH Soil Amendments on Construction Sites 10
Purpose
This section establishes procedures for implementing BMPs when using high pH soil amendments on
construction sites. See Table D.2.2.9.A for a description of the BMPs. This section outlines an expedited
review process and typical approval conditions that will allow contractors and builders to use soil
amendments without impacting water quality. Additional BMPs may be required based upon site specific
conditions that may warrant more protection. This policy is limited to those amendments, defined below,
commonly known to add stability to sloppy soil conditions but which can alter water runoff quality.
10 Excerpted from the King County Stormwater Pollution Prevention Manual (SPPM), BMP Info Sheet #11
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-103
SECTION D.2.2 SWPPS MEASURES
Authority: KCC 9.12.025 prohibits discharges of polluted or contaminated water into surface or storm
water drainage systems. The purpose of this statute is to protect surface and ground water by regulating the
discharge of potentially contaminated surface water. If soil amendments are proposed with an initial
application, an environmental review is required, under SEPA, which assesses impacts, provides public
input and mitigated conditions for its use.
King County Road Design and Construction Standards, Sections 4.04 and 4.05 also require an engineered
design for use of a soil amendment on road surfaces or around drainage systems. The design may
incorporate a thorough assessment of soil composition and laboratory analysis. The Surface Water Design
Manual authorizes DPER to adopt BMPs for the control and protection of surface water. Currently, for all
sites, the BMPs established in this policy are the minimum standards that shall be applied.
Procedure
An applicant may apply for use of soil amendments allowed under this policy anytime during the permit
application review or after the permit has been issued and site construction is underway. After making a
submittal to DPER, the applicant may receive approval conditions. Conditions may vary from site to site,
but typically will include many of the BMPs included in this policy.
Applicants should identify any use of soil amendments as early in the process as possible to avoid delays
in obtaining approval for use during the construction phase. If a site has known soil and water conditions
that might make work during rainy periods difficult, they may want to plan to use soil amendments on
their site. Obviously, if this issue is addressed at the permit review phase, implementation in the field can
occur without delay. However, because of the potential risks of surface water pollution discharge and
required treatment, an environmental assessment will be necessary before conditions for use can be
established.
Limitations
This policy applies to the intended use of soil amendments in areas that will be covered by impervious
surfaces. For areas not covered by impervious surfaces, additional reviews, study, and BMPs may be
required. In addition, alterations to original approved use plans will require a resubmittal for approval.
Approval for the use of the soil amendments in unincorporated King County can only occur by strictly
following the procedures contained herein and not by any other approval obtained from DPER.
Submittal Requirements
To obtain approval for the use of soil amendments allowed under this policy, the applicant shall prepare a
submittal package to DPER that includes the following:
• Letter to DPER requesting use of soil amendments at a construction site allowed under this policy.
• Document or letter attachment that identifies source of materials and description of mixing and
laydown process, plan for disposal of treated contact water, sanitary sewer permits and/or BMPs, and
special precautions proposed to prevent the contamination of surface or stormwater drainage systems,
other than 'sealed' drainage systems.
• Site Plan: Show a site plan map which:
1) Shows overall grading plan showing existing and proposed contours.
2) Identifies sensitive areas and permanent or temporary drainage facilities.
3) Identifies areas that soil amendment is planned.
4) Shows depths of application and percent of amendment to be used.
5) Shows location of special wheel wash facility.
6) Shows location of collection and conveyance swales or pipes for contact water.
7) Shows location of sealed storage/treatment tanks or temporary ponds (fully lined).
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D.2.2.9 USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES
8) Identifies any discharge point from the site into natural drainage systems.
9) Includes soil log locations that identify seasonal high groundwater areas.
• Report and analysis of engineering mix design which includes depths of application and percent of
amendment usage.
• For proposals that use CKD and CKD additive, provide analysis of source material for soluble
contaminants. Include a description of fuel source.
• Monitoring criteria, including locations for pH and turbidity testing.
• Provide contingency plan should use of soil amendment and site and weather conditions result in
polluted or contact water entering natural drainage systems.
• Provide contact information or water quality specialist assigned to monitor application of soil
amendments and BMPs.
If the project is under construction, the applicant shall contact the DPER inspector assigned to the project
to initiate a review for compliance with the BMPs and requirements herein. Otherwise contact the planner
or engineer assigned to review the permit or land use application.
Review and Approval
Once the review has been completed, the applicant shall be notified by letter which stipulates the
conditions of approval. Prior to authorizing the use of soil amendments at the site, the applicant shall
provide a special restoration financial guarantee cash deposit in the amount as determined by the existing,
established processes. Note: It remains the applicant/contractor’s responsibility to comply with any other
applicable state or federal regulations such as use of NIOSH respiratory protection, safety goggles, gloves
and protective clothing whenever using hazardous materials.
Applicable Standards
Typically, all proposals using soil amendments in unincorporated King County shall have these conditions
as standard requirements:
1. Prior to any application of CKD/CTB, the general contract shall hold a preconstruction meeting with
the assigned DPER inspector at least 3 working days in advance.
2. CKD will not be permitted for use in areas adjacent to or in proximity to wetlands and streams areas.
CTB may or may not be permitted in these areas.
3. Areas not covered by impervious surfaces:
• CKD will not be permitted in areas that will not be covered by impervious surfaces.
• If CTB is proposed in these areas, an analysis of whether or not the soil amendment will change
the post-development runoff characteristics and the permanent stormwater facilities were sized
appropriately shall be submitted for review. Use of CTB in areas not permanently covered by
impervious surface may require re-sizing of the permanent stormwater facilities.
4. If CKD is proposed, the contractor shall provide mill certificates verifying the product composition.
The contractor/developer must be prepared to follow BMPs during and after soil treatment and be
prepared to treat runoff from the treatment area(s) immediately. All stormwater collection systems
must be in place and all equipment (pH meters, dry ice, etc.) must be onsite.
5. Collection of stormwater (see BMP #5 in Table D.2.2.9.A):
• Stormwater from the application area shall be kept separate from and prevented from comingling
with uncontaminated stormwater.
• During the application of CKD/CTB, stormwater runoff shall be collected in temporary collection
systems and shall not be allowed to enter the permanent facilities. Permanent drainage systems
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SECTION D.2.2 SWPPS MEASURES
shall be capped to prevent contact stormwater from entering the inlets of the catch basins.
Stormwater from the application area shall not be collected in the temporary/permanent detention
ponds, even if the underlying soils are 'impermeable'.
6. Treatment: If necessary, pH adjustment shall be done in the collection tanks or temporary ponds and
not in the permanent detention ponds.
7. Disposal options: The proposal to use CKD/CTB must contain a disposal plan that may include one or
a combination of sanitary sewer or approved offsite disposal. Treated contact water may be discharged
to the sanitary sewer if authorizations are obtained from the King County Industrial Waste Program
(206-263-3000) and the local sewer district. All discharge conditions (e.g. pH, settleable solids) must
be followed. If a sanitary sewer is not available at the site, contact water may be transported offsite to
an approved site for disposal and proof of proper disposal must be submitted to King County. All
authorizations for disposal shall be obtained prior to CKD/CTB application.
• Infiltration: Depending on the site conditions, pH-adjusted stormwater may be infiltrated. Prior to
infiltration, pH must be between 6.5 and 8.5.
• Surface Water: Contact water from the application area shall not be discharged to surface waters,
even if treatment has adjusted the pH.
8. Emergency backup plan: An emergency backup plan must be prepared and ready to implement to
handle large quantities of stormwater.
9. Monitoring shall be conducted to determine that contact stormwater is not leaving the site. Offsite
monitoring shall also be conducted to identify impacts to adjacent water bodies. Bonding may be
required to cover mitigation of impacts and restoration.
10. A soils specialist will establish the mixing percentage for onsite soils. Soil amendments will never
occur in excess of the ability of the onsite equipment and resources to meet all BMP requirements.
11. For sites one acre or larger, a National Pollutant Discharge Elimination System (NPDES)
Construction Stormwater permit must be obtained from Ecology. NPDES permits and 'Stormwater
Pollution Prevention Plans (SWPPPs) must be amended and the use of CKD/CTB must be approved
by Ecology prior to application.
The contractor/developer shall comply will all federal, state, and local regulations. A health and safety
plan may be required for the protection of King County inspectors.
Additional BMPs may be applicable depending on mix design, proximity of wetlands or streams (e.g.
within 300 feet of class/type I and 100 feet or less for other types) and site conditions.
D.2.2.10 MAINTAIN PROTECTIVE BMPS
Pollutant protection measures shall be maintained to assure continued performance of their intended
function. Reporting and documentation shall be kept current and made available to DPER as indicated.
Purpose: The purpose of maintaining protective BMPs is to provide effective pollutant protection when
and where required by the plan and the project, and to provide timely and relevant project information.
When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum,
continuously during operation, and promptly maintained to fully functioning condition as necessary to
assure continued performance of their intended function. Documentation shall be kept current per specific
BMP requirements.
Measures to Use:
1. Maintain and repair all pollutant control BMPs as needed to assure continued performance of their
intended function in accordance with BMP specifications.
2. Maintain and repair storage locations for equipment and materials associated with BMP processes.
Conduct materials disposal in compliance with County regulatory requirements.
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D.2.2.11 MANAGE THE PROJECT
3. As required, provide current reporting and performance documentation at an accessible location for
the site inspector and other DPER staff.
4. Remove all temporary pollutant control BMPs prior to final construction approval, or within 30 days
after achieving final site stabilization or after the temporary BMPs are no longer needed.
D.2.2.11 MANAGE THE PROJECT
SWPPP requirements shall be implemented and managed as part of the overall CSWPP plan. Concrete
construction and its impacts are primary among pollutant concerns on site development projects. Fueling
operations and materials containment of treatment chemicals and other project materials are also typical
pollutant concerns. Operations that produce these and other pollutants are often conducted by
subcontractors and their laborers, yet may require specific protective measures, documentation and
reporting. Protective measures and BMPs need to be made available prior to construction and suitable
oversight provided to assure inspection, monitoring and documentation requirements are met.
Projects shall assign a qualified CSWPP Supervisor (Section D.2.3.1) to be the primary contact for
SWPPP and ESC issues and reporting, coordination with subcontractors and implementation of the
CSWPP plan as a whole.
Measures to Use:
1. Phase development projects to the maximum degree practicable and take into account seasonal work
limits.
2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued
performance of their intended function. Conduct site inspections and monitoring in accordance with
the Construction Stormwater General Permit and King County requirements. Coordinate with
subcontractors and laborers to assure the SWPPP measures are followed.
3. Documentation and reporting: – Inspect, maintain, and repair all BMPs as needed to assure continued
performance of their intended function. Document site inspections and monitoring in accordance with
the Construction Stormwater General Permit, specific BMP conditions and King County
requirements. Log sheets provided in Reference Section 8 may be used if appropriate. Follow
reporting requirements and provide documentation as requested to DPER staff.
4. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in
accordance with the Construction Stormwater General Permit and King County requirements. Obtain
approval for specific SWPPP measures (e.g., chemical treatments of stormwater) well in advance of
need. Coordinate SWPPP plan updates with the site inspector (see Section D.2.4.1).
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SECTION D.2.3 CSWPP PERFORMANCE AND COMPLIANCE PROVISIONS
D.2.3 CSWPP PERFORMANCE AND COMPLIANCE PROVISIONS
The changing conditions typical of construction sites call for frequent field adjustments of existing ESC
and SWPPS measures or additional ESC and SWPPS measures in order to meet required performance. In
some cases, strict adherence to specified measures may not be necessary or practicable based on site
conditions or project type. In other cases, immediate action may be needed to avoid severe impacts.
Therefore, careful attention must be paid to ESC and SWPPS performance and compliance in accordance
with the provisions contained in this section.
D.2.3.1 CSWPP SUPERVISOR
For projects in Targeted, Full, or Large Project Drainage Review, or projects in Directed Drainage Review
as determined by the DPER permit reviewer, the applicant must designate an CSWPP supervisor who
shall be responsible for the performance, maintenance, and review of ESC and SWPPS measures and for
compliance with all permit conditions relating to CSWPP as described in the CSWPP Standards. The
applicant's selection of a CSWPP supervisor must be approved by King County. (County approval may be
rescinded for non-compliance, requiring the applicant to select another CSWPP supervisor and obtain
County approval prior to continuing work on the project site.)
For projects that disturb one acre or more of land, the CSWPP supervisor must be a Certified
Professional in Erosion and Sediment Control (see www.cpesc.net for more information) or a Certified
Erosion and Sediment Control Lead whose certification is recognized by King County.11 King County
may also require a certified ESC professional for sites smaller than one acre of disturbance if DPER
determines that onsite ESC measures are inadequately installed, located, or maintained.
For larger, more sensitive sites, King County may require a certified ESC professional with several years
of experience in construction supervision/inspection and a background in geology, soil science, or
agronomy. Typically, if a geotechnical consultant is already working on the project, the consultant may
also be a certified ESC professional designated as the CSWPP supervisor. The design engineer may also
be qualified for this position. This requirement shall only be used for sensitive sites that pose an unusually
high risk of impact to surface waters as determined by DPER. At a minimum, the project site must meet
all of the following conditions in order to require the applicant to designate as the CSWPP supervisor a
certified ESC professional with such expertise:
• Alderwood soils or other soils of Hydrologic Group C or D
• Five acres of disturbance
• Large areas (i.e., two or more acres) with slopes in excess of 10 percent.
Proximity to streams or wetlands or phosphorus-sensitive lakes, such as Lake Sammamish, shall also be a
factor in determining if such expertise in the CSWPP supervisor is warranted. However, proximity alone
shall not be a determining factor because even projects that are a considerable distance from surface
waters can result in significant impacts if there is a natural or constructed drainage system with direct
connections to surface waters.
The name, address, and phone number of the CSWPP supervisor shall be supplied to the County prior to
the start of construction. A sign shall be posted at all primary entrances to the site identifying the CSWPP
supervisor and his/her phone number. The requirement for a CSWPP supervisor does not relieve the
applicant of ultimate responsibility for the project and compliance with King County Code.
11 King County recognition of certification means that the individual has taken a King County-approved third party training
program and has passed the King County-approved test for that training program.
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D.2.3.3 ESC PERFORMANCE
D.2.3.2 MONITORING OF DISCHARGES
The CSWPP supervisor shall have a turbidity meter onsite and shall use it to monitor surface and storm
water discharges from the project site and into onsite wetlands, streams, or lakes whenever runoff occurs
from onsite activities and during storm events. The CSWPP supervisor shall keep a log of all turbidity
measurements taken onsite and make it available to DPER upon request. If the project site is subject to a
NPDES general permit for construction issued by the Washington State Department of Ecology (Ecology),
then the project must comply with the monitoring requirements of that permit.
The CSWPP supervisor shall also use the specific SWPPS BMP procedures for monitoring surface and
stormwater discharge for pollutants and acceptable discharge levels. The CSWPP supervisor shall keep
logs as required by the procedures of all measurements taken onsite and make them available to DPER on
request.
D.2.3.3 ESC PERFORMANCE
ESC measures shall be applied/installed and maintained so as to prevent, to the maximum extent
practicable, the transport of sediment from the project site to downstream drainage systems or surface
waters or into onsite wetlands, streams, or lakes or onto adjacent properties. This performance is intended
to be achieved through proper selection, installation, and operation of the above ESC measures as detailed
in the CSWPP Standards (detached Appendix D) and approved by the County. However, the CSWPP
supervisor designated per Section D.2.3.1 or the County may determine at any time during construction
that such approved measures are not sufficient and additional action is required based on one of the
following criteria:
1. IF a turbidity test of surface and storm water discharges leaving the project site is greater than the
benchmark value of 25 NTU (nephelometric turbidity units) set by the Washington State Department of
Ecology, but less than 250 NTU, the CSWPP Supervisor shall do all of the following:
a) Review the ESC plan for compliance and make appropriate revisions within 7 days of the
discharge that exceeded the benchmark of 25 NTU, AND
b) Fully implement and maintain appropriate ESC measures as soon as possible but no later than 10
days after the discharge that exceeded the benchmark, AND
c) Document ESC implementation and maintenance in the site log book.
2. IF a turbidity test of surface or storm water entering onsite wetlands, streams, or lakes indicates a
turbidity level greater than 5 NTU above background when the background turbidity is 50 NTU or
less, or 10% above background when the background turbidity is greater than 50 NTU, then corrective
actions and/or additional measures beyond those specified in SWDM Section 1.2.5.1 shall be
implemented as deemed necessary by the County inspector or onsite CSWPP supervisor.
3. IF discharge turbidity is 250 NTU or greater, the CSWPP Supervisor shall do all of the following:
a) Notify the County by telephone, AND
b) Review the ESC plan for compliance and make appropriate revisions within 7 days of the
discharge that exceeded the benchmark of 25 NTU, AND
c) Fully implement and maintain appropriate ESC measures as soon as possible but no later than 10
days after the discharge that exceeded the benchmark, AND
d) Document ESC implementation and maintenance in the site log book. AND
e) Continue to sample discharges until turbidity is 25 NTU or lower, or the turbidity is no more than
10% over background turbidity.
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SECTION D.2.3 CSWPP PERFORMANCE AND COMPLIANCE PROVISIONS
4. IF the County determines that the condition of the construction site poses a hazard to adjacent
property or may adversely impact drainage facilities or water resources, THEN additional
measures beyond those specified in SWDM Section 1.2.5.1 may be required by the County.
D.2.3.4 SWPPS PERFORMANCE
SWPPS measures shall be applied/installed and maintained so as to prevent, reduce, or eliminate the
discharge of pollutants to onsite or adjacent stormwater systems or watercourses or onto adjacent
properties. This performance is intended to be achieved through proper selection, installation, and
operation of the above SWPPS measures as detailed in the CSWPP Standards (detached Appendix D) and
approved by the County. However, the CSWPP supervisor designated per Section D.2.3.1 or the County
may determine at any time during construction that such approved measures are not sufficient and
additional action is required based on the criteria described in the specific SWPPS BMP standard and/or
conditions of an approved adjustment.
D.2.3.5 FLEXIBLE COMPLIANCE
Some projects may meet the intent of Core Requirement #5 while varying from specific CSWPP
requirements in this appendix. If a project is designed and constructed such that it meets the intent of core
requirement, the County may determine that strict adherence to a specific ESC requirement is unnecessary;
an approved adjustment (see Section 1.4) from the SWDM is not required in these circumstances. Certain
types of projects are particularly likely to warrant this greater level of flexibility; for instance, projects on
relatively flat, well drained soils, projects that are constructed in closed depressions, or projects that only
disturb a small percentage of a forested site may meet the intent of this requirement with very few ESC
measures. Note, however, that SWPPS requirements may actually be emphasized on well-drained soils,
particularly in groundwater protection or well-protection areas, or in close proximity to water bodies.
D.2.3.6 ROADS AND UTILITIES COMPLIANCE
Road and utility projects often pose difficult erosion control challenges because they frequently cross
surface waters and because narrow right-of-way constrains areas available to store and treat sediment-
laden water. In most cases, the standards of this appendix may be applied to such linear projects without
modification. For instance, the ability to use perimeter control rather than a sediment retention facility for
small drainage areas (see Section D.2.1.3) will apply to many of these projects.
However, there may be some projects that cannot reasonably meet the standards of Core Requirement #5
and this appendix. In these cases, other measures may be proposed that will provide reasonable
protection. An adjustment is not required for such projects, unless the County determines that measures
proposed by the applicant fail to meet the intent of Core Requirement #5 and this appendix, and that
significant adverse impacts to surface water may result. Examples of other measures that may be taken in
lieu of the standards of this appendix are:
1. Phasing the project so that the site is worked progressively from end to end, rather than clearing and
grubbing the entire length of the project. This results in smaller exposed areas for shorter durations,
thus reducing the erosion risk. It is recommended that there be no more than 500 feet of open trench
during any phase of construction.
2. Placement of excavated materials from utility trenches on the upslope side of the excavation, to
minimize transport of sediment outside of the project area.
3. Mulching and vegetating cut and fill slopes as soon as they are graded. Frequently, this is done at the
end of construction when paving or utility installation is complete. Vegetating these areas at the start
of the project stabilizes those areas most susceptible to erosion.
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D.2.3.7 ALTERNATIVE AND EXPERIMENTAL MEASURES
4. Protecting all catch basin inlets with catch basin inserts or other inlet protection when these do not
drain to ponds or traps. This will not provide the same level of protection as a sediment pond or trap,
but can remove most of the sand-sized material entrained in the runoff.
5. Phasing the project so that all clearing and grading in critical area buffers occurs in the dry season.
This substantially reduces the chance of erosion and allows for rapid revegetation in the late summer
and early fall.
6. Using approved flocculent or other chemical treatment approved by King County to reduce the
turbidity of water released from sediment ponds.
7. Hiring a private consultant with expertise in ESC to review and monitor the site.
8. Limiting employee/contractor parking and overnight/weekend parking of construction vehicles to
dedicated and controlled areas prepared for drip and spill control. Options in the right-of-way for
such areas can be limited.
If alternatives are used, it may be appropriate to develop a monitoring program that would monitor
compliance with the performance standard of Core Requirement #5 and/or impacts to nearby water
resources. Of particular concern are impacts to salmonid spawning gravels. McNeil sampling is a
possible method of sampling to determine impacts to spawning gravels (see Section D.2.4.3).
D.2.3.7 ALTERNATIVE AND EXPERIMENTAL MEASURES
In general, the King County Surface Water Design Manual only contains those BMPs that are standards of
the local industry. There are a variety of other BMPs available that may also be used, even though they
are not included in this appendix. Such alternatives may be approved without an adjustment if the
alternative will produce a compensating or comparable result with the measures in this appendix.
Variations on or modifications of the BMPs in this appendix may also be granted based on the same
criteria. Technical support will be provided by WLRD when requested by DPER.
An adjustment is only required for those products or techniques that are so new and untested as to be
experimental. If the County determines that a proposed alternative is experimental, then an experimental
adjustment must be obtained (see Section 1.4.4 of the SWDM). In addition, the new product or technique
must be approved through the state Department of Ecology's CTAPE program.12 The intent of this
requirement is not to discourage new techniques, but to insure that new techniques are monitored and
documented for adequacy and possible inclusion in subsequent versions of the SWDM. An example of a
product that would have required an experimental adjustment prior to this version of the manual is the
catch basin insert (see Section D.2.1.5.3) because it was not equivalent to any existing measure.
12 CTAPE stands for Chemical Technology Assessment Protocol – Ecology. For more information, see Ecology's website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/tape_ctape.html .
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SECTION D.2.4 CSWPP IMPLEMENTATION REQUIREMENTS
D.2.4 CSWPP IMPLEMENTATION REQUIREMENTS
This section describes the CSWPP implementation requirements that are required at each construction site.
The measures and practices correspond to the implementation requirements in Core Requirement #5.
Three of the sections (the CSWPP report (Section D.2.4.1, below), CSWPP maintenance requirements
(Section D.2.4.4, p. D-114), and final site stabilization (Section D.2.4.5, p. D-115)) are required of every
project. The rest of the sections are special requirements that may apply to the project depending on site
conditions and project type. The introductory paragraphs at the beginning of most sections present the
purpose of the measures and when they should be applied to the site. Compliance with the implementation
requirements (as appropriate for the site) ensures compliance with the CSWPP measures. Note, however,
that additional measures shall be required by the County if the existing standards are insufficient to protect
adjacent properties, drainage facilities, or water resources.
D.2.4.1 CSWPP PLAN
A CSWPP plan, containing the ESC plan and the SWPPS plan, and showing the location and details of
ESC and SWPPS measures, is required for all proposed projects. It shall include a CSWPP report, which
includes supporting information for providing ESC and SWPPS measures and meeting CSWPP
implementation requirements. A copy of the CSWPP plan with CSWPP report shall be kept at the project
site throughout all phases of construction. All of the materials required for the CSWPP report are standard
parts of engineering plan submittals for projects requiring drainage review. The simplest approach to
preparing this report is to compile the pieces during preparation for submittal and include the report as a
separate part of the CSWPP plan submittal package. The CSWPP report shall include the following:
1. A detailed construction sequence, as proposed by the design engineer or erosion control specialist,
identifying required ESC measures and implementation requirements;
2. A technical information report (TIR) and ESC and SWPPS plans for King County review in
accordance with Sections 2.3.1 and 2.3.3 of the King County Surface Water Design Manual (SWDM).
Incorporate any King County review comments as necessary to comply with Core Requirement #5 of
the SWDM (Section 1.2.5) and the Construction Stormwater Pollution Prevention Standards in this
appendix;
3. Any calculations or information necessary to size ESC measures and demonstrate compliance with
Core Requirement #5;
4. Descriptions and any supporting documentation, operating procedures, precautions, logging and
reporting requirements etc. for the project’s SWPPS BMPs,
5. An inspection and maintenance program in accordance with Section D.2.4.4 (p. D-114) that
includes the designation of a certified CSWPP supervisor as point of contact; and
6. Anticipated changes or additions necessary during construction to ensure that ESC and SWPPS
measures perform in accordance with Core Requirement #5 and Sections D.2.1 (p. D-10) and D.2.2
(p. D-74).
While the CSWPP plan focuses on the initial measures to be applied to the site, any changes or additions
necessary during construction to ensure that ESC and SWPPS measures perform in accordance with Core
Requirement #5 and Sections D.2.1, D.2.2 and D.2.4 must be identified in the CSWPP report. The
County may require large, complex projects to phase construction and submit multiple ESC plans for
different stages of construction. Development of new CSWPP plans is not required for changes that are
necessary during construction.
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D.2.4.2 WET SEASON REQUIREMENTS
D.2.4.2 WET SEASON REQUIREMENTS
Any site with exposed soils during the wet season (October 1 to April 30) shall be subject to the special
provisions below. In addition to the ESC cover measures (see Section D.2.1.2, p. D-12), these provisions
include covering any newly seeded areas with mulch and identifying and seeding as much disturbed area
as possible prior to September 23 in order to provide grass cover for the wet season. A "wet season ESC
plan" must be submitted and approved by the County before work proceeds or continues.
Wet Season Special Provisions
All of the following provisions for wet season construction are detailed in the referenced sections. These
requirements are listed here for the convenience of the designer and the reviewer.
1. The allowed time that a disturbed area may remain unworked without cover measures is reduced to
two consecutive working days, rather than seven (Section D.2.1.2).
2. Stockpiles and steep cut and fill slopes are to be protected if unworked for more than 12 hours
(Section D.2.1.2).
3. Cover materials sufficient to cover all disturbed areas shall be stockpiled on site (Section D.2.1.2).
4. All areas that are to be unworked during the wet season shall be seeded within one week of the
beginning of the wet season (Section D.2.1.2.6).
5. Mulch is required to protect all seeded areas (Section D.2.1.2.2).
6. Fifty linear feet of silt fence (and the necessary stakes) per acre of disturbance must be stockpiled on
site (Section D.2.1.3.1).
7. Construction road and parking lot stabilization are required for all sites unless the site is underlain by
coarse-grained soil (Section D.2.1.4.2).
8. Sediment retention is required unless no offsite discharge is anticipated for the specified design flow
(Section D.2.1.5).
9. Surface water controls are required unless no offsite discharge is anticipated for the specified design
flow (Section D.2.1.6).
10. Phasing and more conservative BMPs must be evaluated for construction activity near surface waters
(Section D.2.4.3).
11. Any runoff generated by dewatering may be required to discharge to the sanitary sewer (with
appropriate discharge authorization), portable sand filter systems, or holding tanks (Section D.2.2).
D.2.4.3 CRITICAL AREAS RESTRICTIONS
Any construction that will result in disturbed areas on or within a stream or associated buffer, a wetland or
associated buffer, or within 50 feet of a lake shall be subject to the special provisions below. These
provisions include, whenever possible, phasing the project so that construction in these areas is limited to
the dry season. The County may require more conservative BMPs, including more stringent cover
requirements, in order to protect surface water quality. Any project proposing work within 50 feet of a
steep slope hazard area shall evaluate the need for diverting runoff that might flow over the top of the
slope.
Critical Areas Special Provisions
Any project that disturbs areas on or within a stream or associated buffer, wetland or associated buffer, or
within 50 feet of a lake has the potential to seriously damage water resources, even if the project is
relatively small. While it is difficult to require specific measures for such projects because the CSWPP
2016 Surface Water Design Manual – Appendix D 4/24/2016 D-113
SECTION D.2.4 CSWPP IMPLEMENTATION REQUIREMENTS
plan must be very site specific, the following recommendations shall be incorporated into the plan where
appropriate:
1. Whenever possible, phase all or part of the project so that it occurs during the dry season. If this is
impossible, November through February shall be avoided since this is the most likely period for large,
high-intensity storms.
2. All projects shall be completed and stabilized as quickly as possible. Limiting the size and duration of
a project is probably the most effective form of erosion control.
3. Where appropriate, sandbags or an equivalent barrier shall be constructed between the project area
and the surface water in order to isolate the construction area from high water that might result due to
precipitation.
4. Additional perimeter protection shall be considered to reduce the likelihood of sediment entering the
surface waters. Such protection might include multiple silt fences, silt fences with a higher AOS,
construction of a berm, or a thick layer of organic mulch upslope of a silt fence.
5. If work is to occur within the ordinary high water mark of a stream, most projects must isolate the
work area from the stream by diverting the stream or constructing a cofferdam. Certain small projects
that propose only a small amount of grading may not require isolation since diversions typically result
in disturbance and the release of some sediment to the stream. For such small projects, the potential
impacts from construction with and without a diversion must be weighed.
6. If a stream must be crossed, a temporary bridge shall be considered rather than allowing equipment to
utilize the streambed for a crossing.
For projects in or near a salmonid stream, it may be appropriate to monitor the composition of any
spawning gravels within a quarter-mile of the site with a McNeil sampler or similar method approved by
King County before, during, and after construction. The purpose of such monitoring would be to
determine if the fine content of the gravels increases as a result of construction impacts. Monitoring
results could be used to guide erosion control efforts during construction and as a threshold for replacing
spawning gravels if the fine content rises significantly.
D.2.4.4 MAINTENANCE REQUIREMENTS
All ESC and SWPPS measures shall be maintained and reviewed on a regular basis as prescribed in the
maintenance requirements for each BMP and in this section. The CSWPP supervisor shall review the site
for ESC and SWPPS at least weekly and within 24 hours of significant storms. The CWSPP supervisor
shall also review the site for ESC and SWPPS during periods of active construction where maintenance
conditions change with construction activity (e.g., site grading operations, or concrete construction and
dewatering operations for a detention vault). The County requires a written record of these reviews be
kept on site with copies submitted to DPER within 48 hours.
Documentation
If DPER requires that a written record be maintained, standard ESC and SWPPS Maintenance Reports
forms, included in Section D.4.1 (p. D-137), may be used. A copy of all the required maintenance reports
shall be kept on site throughout the duration of construction. Detailed maintenance requirements for each
ESC measure are provided in Section D.2.1. Maintenance requirements for SWPPS BMPs are specified
in Section D.2.2 (as in the case of BMPs related to concrete handling or material containment) or may be
specified as part of a treatment or monitoring program, often accompanied with adjustment conditions of
approval.
Review Timing
Weekly reviews shall be carried out every 6 to 8 calendar days. Reviews shall also take place within 24
hours of significant storms. In general, a significant storm is one with more than 0.5 inches of rain in 24
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D.2.4.5 FINAL STABILIZATION
hours or less. Other indications that a storm is "significant" are if the sediment ponds or traps are filled
with water, or if gullies form as a result of the runoff.
Note: The site is to be in compliance with the regulations of this appendix at all times. The requirement
for periodic reviews does not remove the applicant's responsibility for having the site constantly in
compliance with Core Requirement #5 and the requirements of this appendix. The reviews are a
mechanism to ensure that all measures are thoroughly checked on a regular basis and that there is
documentation of compliance. The requirement for these reviews does not mean that CSWPP is to be
ignored in between.
D.2.4.5 FINAL STABILIZATION
Prior to obtaining final construction approval, the site shall be stabilized, the structural ESC and SWPPS
measures (such as silt fences, sediment traps, and concrete waste collection pits) removed, and drainage
facilities cleaned. The removal of ESC and SWPPS measures is not required for those projects, such as
plats, that will be followed by additional construction under a different permit. In these circumstances, the
need for removing or retaining the measures must be evaluated on a site-specific basis.
To obtain final construction approval, the following conditions must be met:
1. All disturbed areas of the site shall be vegetated or otherwise permanently stabilized. At a
minimum, disturbed areas shall be seeded and mulched (see Section D.2.1.2.6) with a high likelihood
that sufficient cover will develop shortly after final approval. Mulch without seeding is not adequate
to allow final approval of the permit, except for small areas of mulch used for landscaping. The only
exceptions to these requirements are lots within a plat that are to be developed under an approved
residential permit immediately following plat approval. In these cases, mulch and/or temporary
seeding are adequate for cover.
2. Structural measures such as, but not limited to, silt fences, pipe slope drains, construction entrances,
storm drain inlet protection, sediment traps and ponds, concrete washout and collection pits, and
pollutant storage shall be removed from the site. Measures that will quickly decompose, such as brush
barriers and organic mulches, may be left in place. In the case of silt fences, it may be best to remove
fences in conjunction with the seeding, since it may be necessary to bring machinery back in to
remove them. This will result in disturbed soils that will again require protection. The DPER
inspector must approve an applicant's proposal to remove fencing prior to the establishment of
vegetation. In some cases, such as residential building following plat development, it shall be
appropriate to leave some or all ESC measures for use during subsequent development. This shall be
determined on a site-specific basis.
3. All permanent surface water facilities, including catch basins, manholes, pipes, ditches, channels, flow
control facilities, and water quality facilities, shall be cleaned. Existing and newly constructed flow
control BMP facilities shall be cleaned and/or mitigated as necessary to restore functionality. Any
offsite catch basin that required protection during construction (see Section D.2.1.5.3) shall also be
cleaned.
4. If only the infrastructure of the site has been developed (e.g., subdivisions and short plats) with
building construction to occur under a different permit, then the critical area buffers, Critical Area
Tracts, or Critical Area Setback Areas shall be clearly marked as described in Section D.2.1.1 (p. D-
11) in order to alert future buyers and builders.
D.2.4.6 NPDES REQUIREMENTS
As part of the implementation of the National Pollutant Discharge Elimination System (NPDES), projects
that will disturb one or more acres for purposes of constructing or allowing for construction of a
development, or projects disturbing less than one acre that are part of a larger common plan of
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SECTION D.2.4 CSWPP IMPLEMENTATION REQUIREMENTS
development or sale 13 that will ultimately disturb one or more acres, must apply for coverage under the
Washington State Department of Ecology's (Ecology) Construction Stormwater General Permit. In
general, the construction stormwater pollution prevention plan required by the King County Surface Water
Design Manual is equivalent to that required by the State through the Stormwater Management Manual
for Western Washington (Ecology, 2014). The Ecology stormwater permit application requires the filing
of a Notice of Intent (NOI) at least 30 days prior to the start of construction. The only major requirement
of the stormwater permit that is not included in the SWDM is a public notice requirement. Note that this
public notice for Ecology's stormwater permit may be published concurrently with other public notices
required for permits or SEPA. Contact Ecology at (360) 407-7156 for complete information on permit
thresholds, applications, and requirements.
13 Common plan of development or sale means a site where multiple separate and distinct construction activities may take
place at different times or on different schedules, but still under a single plan. Examples include: 1) phased projects and
projects with multiple filings or lots, even if the separate phases or filings/lots will be constructed under separate contract or by
separate owners (e.g. a development where lots are sold to separate builders); 2) a development plan that may be phased
over multiple years, but is still under a consistent plan for long-term development; and 3) projects in a contiguous area that
may be unrelated but still under the same contract, such as construction of a building extension and a new parking lot at the
same facility.
D.2.4.7 FOREST PRACTICE PERMIT REQUIREMENTS
Projects that will clear more than two acres of forest or 5,000 board feet of timber must apply for a Class
IV Special Forest Practice permit from the Washington State Department of Natural Resources (WSDNR).
All such clearing is also subject to the State Environmental Policy Act (RCW 43.21C) and will require
SEPA review. King County assumes lead agency status for Class IV permits and the application may be
consolidated with the associated King County development permit or approval. The permit must be
initiated with WSDNR, but will then be transferred over to King County to conduct the SEPA review and
grant the permit. Contact the WSDNR for complete information on permit thresholds, applications, and
requirements.
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D.2.5.1 ESC PLAN
D.2.5 CONSTRUCTION STORMWATER POLLUTION PREVENTION
PLANS
This section details the specifications and contents for construction stormwater pollution prevention
(CSWPP) plans, containing erosion and sediment control (ESC) plans and stormwater pollution
prevention and spill control (SWPPS) plans. A CSWPP plan includes the plan's drawings plus a CSWPP
report, which provides all supporting information and any additional direction necessary for implementing
ESC and SWPPS measures and meeting CSWPP implementation requirements. The CSWPP plan must
be submitted to DPER as part of a complete engineering plan to facilitate proper drainage review. A copy
of the approved CSWPP plan (with CSWPP report) must be kept on the project site (see Section D.2.4.1,
p. D-112) at all times during the construction phase.
D.2.5.1 ESC PLAN
ESC Plan General Specifications
The site improvement plan shall be used as the base of the ESC plan. Certain detailed information (e.g.,
pipe catch basin size, stub-out locations, etc.) that is not relevant may be omitted to make the ESC plan
easier to comprehend. At a minimum, the ESC plan shall include all of the information required for the
base map of a site improvement plan (see Table 2.3.1A of the King County Surface Water Design
Manual), as well as existing and proposed roads, driveways, parking areas, buildings and drainage
facilities (including existing and proposed flow control BMPs), utility corridors not associated with
roadways, relevant critical areas 14 and associated buffers, and proposed final topography. A smaller scale
may be used to provide better comprehension and understanding.
The ESC plan shall generally be designed for proposed topography, not existing topography, since rough
grading is usually the first step in site disturbance. The ESC plan shall address all phases of
construction (e.g., clearing, grading, installation of utilities, surfacing, and final stabilization). The
County may require large, complex projects to phase construction and submit multiple ESC plans for
different stages of construction.
The ESC plan outlines the minimum requirements for anticipated site conditions. During construction,
ESC plans shall be revised as necessary by the CSWPP supervisor or as directed by King County to
address changing site conditions, unexpected storm events, or non-compliance with the ESC performance
criteria in Section D.2.3.3 (p. D-109). If non-compliance with the ESC performance criteria occurs, the
plan must be updated within 7 days of inspections or investigations. Implementation of the onsite changes
must occur within 10 days.
The following list provides the basic information requirements for the ESC plan and its supporting
documentation. This information shall be consistent with that in Section 8 of the plan’s technical
information report (TIR) required in the engineering plan submittal (see Section 2.3.1 of the SWDM).
Note that the ESC plan's drawings may be simplified by the use of the symbols and codes provided for
each ESC measure in Section D.2.1. In general, the ESC plan's drawings shall be submitted as a separate
plan sheet(s). However, there may be some relatively simple projects where providing a separate grading
and ESC plan drawing is unnecessary.
1. Identify areas with a high susceptibility to erosion.
2. Provide all details necessary to clearly illustrate the intent of the ESC design.
3. Include ESC measures for all on- and offsite utility construction included in the permit.
14 Relevant critical areas, for the purposes of drainage review, include aquatic areas, wetlands, flood hazard areas, erosion
hazard areas, landslide hazard areas, steep slope hazard areas, and critical aquifer recharge areas.
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SECTION D.2.5 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLANS
4. Specify the construction sequence. The construction sequence shall be specifically written for the
proposed project. An example construction sequence is provided in Reference Section D.4.2 (p. D-
139).
5. Include standard ESC plan notes. Standard ESC and SWPPS Notes are provided in Reference
Section D.4.1 (p. D-137).
6. Include an inspection and maintenance program for ESC measures, including designation of a
certified ESC supervisor and identification of phone numbers for 24-hour contact.
7. Include the basis and calculations for selection and sizing of ESC measures.
8. Include documentation, conditions of approval and discussion of approvals from other agencies for
alternative treatment and/or disposal methods.
ESC Plan Measure-Specific Information
The ESC plan must include the following information specific to applicable ESC measures and
implementation requirements. As noted above, this information may need to be updated or revised during
the life of the project by the CSWPP supervisor or as directed by King County.
Clearing Limits
1. Delineate clearing limits (areas to remain uncleared) and flow control BMP area protection limits.
2. Provide details sufficient for installation of markings for maintenance of clearing limits and protection
limits.
Cover Measures
1. Specify the type and location of temporary cover measures to be used on site.
2. If more than one type of cover measure is to be used on site, indicate the areas where the different
measures shall be used, including steep cut and fill slopes.
3. If the type of cover measures to be used will vary depending on the time of year, soil type, gradient, or
some other factor, specify the conditions that control the use of the different measures.
4. Specify the nature and location of permanent cover measures. If a landscaping plan is prepared, this
may not be necessary.
5. Specify the approximate amount of cover measures necessary to cover all disturbed areas.
6. If netting, blankets, or plastic sheeting are specified, provide typical details sufficient for installation
and maintenance.
7. Specify the mulch types, seed mixes, fertilizers, and soil amendments to be used, as well as the
application rate for each item. (Also include fertilizer and application rate information in the SWPPS
documents)
8. For surface roughening, describe methods, equipment and areas where surface roughening will be
use.
9. If PAM is used on a site, show location(s) and describe application method.
10. When compost blankets are used, show site location, application rates, and the name of the supplier
to document that compost meets quality specifications per SWDM Reference 11-C.
Perimeter Protection
1. Specify the location and type of perimeter protection to be used.
2. Provide typical details sufficient for installation and maintenance of perimeter protection.
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D.2.5.1 ESC PLAN
3. If a silt fence is to be used, specify the type of fabric.
4. If compost berms or socks are used, documentation must be provide to assure the supplier meets
quality specifications per SWDM Reference 11-C.
Traffic Area Stabilization
1. Locate the construction entrance(s).
2. Provide typical details sufficient for installation and maintenance of the construction entrance.
3. Locate the construction roads and parking areas.
4. Specify the measure(s) that will be used to create stabilized construction roads and parking areas.
Provide sufficient detail to install and maintain.
5. If a wheel wash or tire bath system will be installed, provide location, typical details for installation
and maintenance.
6. Provide a list of dust control products that will be used onsite and the location of potential application
areas.
Sediment Retention
1. Show the locations of all sedimentation ponds and traps.
2. Dimension pond berm widths and all inside and outside pond slopes.
3. Indicate the trap/pond storage required and the depth, length, and width dimensions.
4. Provide typical section views throughout the pond and outlet structure.
5. If chemical or electrocoagulation treatment of sediment-laden waters will be used, approval
documentation from Ecology must be included.
6. Provide details for disposal of contaminated or chemically treated waters (e.g., where Chitosan or
CO2 have been used).
7. Include here and in the SWPPS plan appropriate approval documentation from local sewer
districts if contaminated or chemically treated water will be discharged to the sanitary sewer.
8. Provide typical details of the control structure and dewatering mechanism.
9. Detail stabilization techniques for the outlet/inlet protection.
10. Provide details sufficient to install cell dividers.
11. Specify mulch and/or recommended cover of berms and slopes.
12. Indicate the required depth gage with a prominent mark at 1-foot depth for sediment removal.
13. Indicate catch basins that are to be protected.
14. Indicate existing and proposed flow control BMP areas that are to be protected.
15. Provide details of the catch basin and flow control BMP protection sufficient to install and
maintain.
Surface Water Control
1. Locate all pipes, ditches, and interceptor ditches, dikes, and swales that will be used to convey
stormwater.
2. Provide details sufficient to install and maintain all conveyances.
3. Indicate locations of outlet protection and provide detail of protections.
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SECTION D.2.5 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLANS
4. Indicate locations and outlets of any possible dewatering systems. Provide details of alternative
discharge methods from dewatering systems if adequate infiltration rates cannot be achieved.
Alternative dewatering systems may also require documentation per the SWPPS plan.
5. Indicate the location of any level spreaders and provide details sufficient to install and maintain.
6. Provide all temporary pipe inverts.
7. Provide location and specifications for the interception of runoff from disturbed areas and the
conveyance of the runoff to a non-erosive discharge point.
8. Provide locations of rock check dams.
9. Provide details, including front and side sections, of typical rock check dams.
Wet Season Requirements
1. Provide a list of all applicable wet season requirements.
2. Clearly identify that from October 1st through April 30th, no soils shall be exposed for more than two
consecutive working days. Also note that this two-day requirement may be applied at other times of
the year if storm events warrant more conservative measures.
3. Clearly identify that exposed soils shall be stabilized at the end of the workday prior to a weekend,
holiday, or predicted rain event.
Critical Areas Restrictions
1. Delineate and label the following critical areas, and any applicable buffers, that are on or adjacent
to the project site: aquatic areas, wetlands, flood hazard areas, erosion hazard areas, landslide hazard
areas, steep slope hazard areas, and critical aquifer recharge areas.
2. If construction creates disturbed areas within any of the above listed critical areas or associated
buffers, specify the type, locations, and details of any measures or other provisions necessary to
comply with the critical area restrictions in Appendix D and protect surface waters and steep
slopes.
D.2.5.2 SWPPS PLAN
SWPPS Plan General Specifications
The SWPPS plan, together with the ESC plan, comprise the construction stormwater pollution prevention
plan (CSWPP) that must be submitted as part of the engineering plans required for drainage review.
The SWPPS plan shall address all phases of construction (e.g., clearing, grading, installation of utilities,
surfacing, and final stabilization). The County may require large, complex projects to phase construction
and submit multiple SWPPS plans for different stages of construction.
The SWPPS plan outlines the minimum requirements for anticipated site conditions and construction
activity. During construction, SWPPS plan shall be revised as necessary by the CSWPP supervisor or
as directed by King County to address changing site conditions or construction activity, unexpected storm
events, or non-compliance with the SWPPS performance criteria in Section D.2.3.4 (p. D-110 ). If non-
compliance with the SWPPS performance criteria occurs (e.g., a pollutant spill), immediate action may be
necessary to address the occurrence; otherwise, the plan must be updated within 7 days of inspections or
investigations. Implementation of the onsite changes must occur within 10 days.
The SWPPS plan must be kept on site during all phases of construction and shall address the
construction-related pollution-generating activities outlined in Subsection A below. The plan must
include a description of the methods the general contractor will use to ensure sub-contractors are aware of
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D.2.5.2 SWPPS PLAN
the SWPPS plan. A form or record must be provided that states all sub-contractors have read and agree
to the SWPPS plan.
A SWPPS plan consists of the following three elements, which are further described in Subsections B, C,
and D below:
1. A site plan with supporting documentation, showing the location and description of BMPs required to
prevent pollution and control spills from construction activities and from chemicals and other
materials used and stored on the construction site. Supporting documentation (see the TIR Section
8 discussion in Section 2.3.1.1 of the KCSWDM) shall include:
• all details necessary to clearly illustrate the intent of the SWPPS design;
• the basis, supporting documentation and approvals, and any calculations for selection and sizing
of SWPPS measures; and
• an inspection and maintenance program for SWPPS measures, including designation of a certified
ESC professional and CSWPP supervisor and identification of phone numbers for 24-hour
contact.
• documentation, conditions of approval and discussion of approvals from other agencies for
treatment and/or disposal methods (e.g., discharge to sanitary sewer, Ecology-approved chemical
treatments)
• The SWPPS plan shall also discuss the receiving waters, especially if the receiving water body
is listed on the 303d list. Information must be provided that shows the plan meets TMDL
requirements. Discuss the 303(d) listed pollutant generated or used onsite and any special
handling requirements or BMPs.
See Subsection B below for more specifics on the SWPPS site plan.
2. A pollution prevention report listing the potential sources of pollution and identifying the
operational, source control, and treatment BMPs necessary to prevent/mitigate pollution from these
sources. See Subsection C below for more specifics on the SWPPS pollution prevention report.
3. A spill prevention and cleanup report describing the procedures and BMPs for spill prevention and
including provisions for cleanup of spills should they occur. See Subsection D below for more
specifics on the SWPPS spill prevention and cleanup report.
A. ACTIVITY-SPECIFIC INFORMATION REQUIRED
At a minimum, the SWPPS plan shall address, if applicable, the following pollution-generating activities
typically associated with construction and include the information specified below for each activity. If
other pollution-generating activities associated with construction of the proposed project are identified, the
SWPPS plan must address those activities in a similar manner.
Storage and Handling of Liquids
1. Identify liquids that will be handled or stored onsite, including but not limited to petroleum products,
fuel, solvents, detergents, paint, pesticides, concrete admixtures, and form oils.
2. Specify types and sizes of containers of liquids that will be stored/handled onsite. Show locations on
the SWPPS site plan.
3. Describe secondary containment methods adequately sized to provide containment for all liquids
stored onsite. Show the locations of containment areas on the SWPPS site plan.
Storage and Stockpiling of Construction Materials and Wastes
1. Identify construction materials and wastes that may be generated or stockpiled onsite. Show the
locations where these materials and wastes will be generated and stockpiled on the SWPPS site plan.
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SECTION D.2.5 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLANS
2. Specify type of cover measures to be used to keep rainwater from contacting construction materials
and wastes that can contribute pollutants to storm, surface, and ground water.
3. If wastes are kept in containers, describe how rainwater will be kept out of the containers.
Fueling
1. Specify method of onsite fueling for construction equipment (i.e. stationary tanks, truck mounted
tanks, wet hosing, etc.). If stationary tanks will be used, show their location on the SWPPS site plan.
2. Describe type and size of tanks.
3. Describe containment methods for fuel spills and make reference to the SWPPS site plan for
location information.
4. If fueling occurs during evening hours, describe lighting and signage plan. Make reference to the
SWPPS site plan for location information.
Maintenance, Repairs, and Storage of Vehicles and Equipment
1. Identify maintenance and repair areas and show their locations on the SWPPS site plan. Use of
drip pans or plastic beneath vehicles is required. A note to this effect must be shown on the SWPPS
site plan.
2. Describe method for collection, storage, and disposal of vehicle fluids.
3. If an area is designated for vehicle maintenance, signs must be posted that state no vehicle washing
may occur in the area. A note to this effect must be shown on the SWPPS site plan.
Concrete Saw Cutting, Slurry, and Washwater Disposal
1. Identify truck washout areas to assure such areas are not within a critical aquifer recharge area. If
they are, the washout area must be lined with an impervious membrane. Show location information
on the SWPPS site plan.
2. Specify size of sumps needed to collect and contain slurry and washwater. Show location information
on the SWPPS site plan.
3. Identify areas for rinsing hand tools including but not limited to screeds, shovels, rakes, floats and
trowels. Show the locations of these areas on the SWPPS site plan.
4. Describe methods for collecting, treating, and disposal of waste water from exposed aggregate
processes, concrete grinding and saw cutting, and new concrete washing and curing water. Do not use
upland land applications for discharging wastewater from concrete washout areas.
Handling of pH Elevated Water
New concrete vaults/structures may cause collected water to have an elevated pH. This water cannot be
discharged to storm or surface water until neutralized.
1. Provide details on treating/neutralizing water when pH is not within neutral parameters.
2. Provide details on disposal of water with elevated pH or of the treated water.
3. If approvals from other agencies for treatment and/or disposal methods (e.g., discharge to
sanitary sewer, Ecology-approved chemical treatments) have been obtained, indicate such approvals
on the plan.
Application of Chemicals including Pesticides and Fertilizers
1. Provide a list of chemicals that may be used on the project site and the application rates.
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D.2.5.2 SWPPS PLAN
2. Describe where and how chemicals will be applied. Show location information on the SWPPS site
plan.
3. Describe where and how chemicals will be stored. Show location information on the SWPPS site
plan.
B. SWPPS SITE PLAN
The site plan element of the SWPPS plan shall include all of the information required for the base map
(see SWDM Table 2.3.1.A), as well as existing and proposed roads, driveways, parking areas, buildings,
drainage facilities, utility corridors not associated with roadways, relevant critical areas 15 and associated
buffers, and proposed final topography. A smaller scale may be used to provide more comprehensive
details on specific locations of each activity and specific prevention measure. In addition to this
information, the following items, at a minimum, shall be provided as applicable:
1. Include SWPPS measures for all on- and offsite utility and roadway construction included in the
permit.
2. Specify the construction sequence. The construction sequence shall be specifically written for the
proposed project. An example construction sequence is provided in Reference Section D.4.2 (p. D-
139).
3. Append to the standard ESC plan notes any site specific SWPPS notes (see ESC Plans General
Specifications above) and specify the construction sequence, including offsite roadway/utility
construction and periods of concentrated construction of concrete structures (e.g., detention vaults).
Standard ESC and SWPPS Notes are provided in the Reference Section. D.4.1 (p. D-137).
4. Identify locations where liquids will be stored and delineate secondary containment areas that will be
provided. (Secondary containment means placing tanks or containers within an impervious structure
capable of containing 110% of the volume contained in the largest tank within the containment
structure. Double-walled tanks do not require additional secondary containment.)
5. Identify locations where construction materials and wastes will be generated and stockpiled.
6. Identify location of fueling for vehicles and equipment if stationary tanks will be used.
7. Delineate containment areas for fuel spills.
8. Show location of lighting and signage for fueling during evening hours.
9. Delineate maintenance and repair areas and clearly note that drip pans or plastic shall be used
beneath vehicles. Also, clearly note that signs must be posted that state no vehicle washing may
occur in the area.
10. Delineate truck washout areas and identify the location of slurry/washwater sumps and rinsing
areas for tools. To assure the wheel wash/tire bath from the ESC plan and the concrete washout areas
are at separate locations, show the location of the wheel wash or tire bath per the ESC plan. (ESC
wheel wash or tire bath wastewater shall not include wastewater from concrete washout areas.)
11. Delineate where chemicals will be applied and identify where they will be stored.
12. Identify where spill response materials will be stored.
13. Indicate whether written approval from Ecology has been obtained for the use of chemical treatment
other than CO2 or dry ice to adjust pH, and provide necessary details and conditions.
15 Relevant critical areas, for the purposes of drainage review, include aquatic areas, wetlands, flood hazard areas, erosion
hazard areas, landslide hazard areas, steep slope hazard areas, and critical aquifer recharge areas.
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SECTION D.2.5 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLANS
C. POLLUTION PREVENTION REPORT
This report provides the specifics on pollution prevention and must include the following information in
addition to the activity-specific information specified in Subsection A above:
1. List the possible sources of pollution per Subsection A above and identify the BMPs to be used for
each source to prevent pollution. Include any supporting information (site conditions, calculations,
etc.) for the selection and sizing of pollution prevention BMPs.
2. Identify the personnel responsible for pollution prevention and clearly list the responsibilities of each
person identified. Contact information for these personnel must be clearly identified in the report
and on the SWPPS site plan.
3. Describe the procedures to be used for monitoring pollution prevention BMPs and for responding to
a BMP that needs attention, including keeping records/reports of all inspections of pollution prevent
BMPs (see Reference Section 4.3 in this appendix) for examples of worksheets that may be used).
D. SPILL PREVENTION AND CLEANUP REPORT
This report provides the specifics on spill prevention and cleanup and must include the following
information in addition to any activity-specific information in Subsection A above related to spill
prevention:
1. List the possible sources of a spill and identify the BMPs to be used for each source to prevent a spill.
2. Identify personnel responsible for spill prevention and cleanup and clearly list the responsibilities of
each person identified. Contact information for these personnel must be clearly identified in the
report and on the SWPPS site plan.
3. Describe the procedures to be used for monitoring spill prevention BMPs and for responding to a
spill incident, including keeping records/reports of all inspections and spills (see Reference Section
4.3 for examples of worksheets that may be used).
4. Identify where spill response materials will be stored. Make reference to the SWPPS site plan for
location information.
5. Identify disposal methods for contaminated water and soil after a spill.
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