Minimum erosion and sediment control Best Management Practices (BMPs) for construction sites in King County
DDES is committed to an effective erosion and sediment control program to protect our streams, lakes, wetlands and the aquatic species that inhabit them. We look forward to working with our customers to meet this goal.
With the listing of the Chinook Salmon and the Bull Trout onto the federal Endangered Species List, erosion and sediment control (ESC) is critical. Section 4(d) of the Endangered Species Act (ESA) actually restricts construction activity from damaging fisheries habitat.
Additional technical assistance in the area of erosion control during the construction of your project is available. DDES inspection staff will offer suggestions to help you stay in compliance with County Code and permit conditions.
At the same time, it is your responsibility to implement and maintain controls on the job site. This needs to be done in a manner that will prevent any silt laden water from leaving the project site or from entering streams, wetlands, and/or off-site drainage systems. Discharge into these areas, along with non-compliance of County standards for ESC, will result in code enforcement action taken on your project.
The 'wet season' occurs from October 1st through April 30th. A guideline of minimum requirements that will help keep your site in compliance is provided below. A complete interpretation of these requirements may be found in Appendix D of the King County Surface Water Design Manual, online at http://your.kingcounty.gov/dnrp/library/water-and-land/stormwater/surface-water-design-manual/appendix-d.pdf (PDF*, 3.1MB). This manual is available at all King County libraries and also may be purchased at King County DDES by calling 206-296-6600.
Keep the ground covered
- Minimize the amount of existing vegetation that you must disturb for construction. Keep out of critical areas and their buffers.
- All disturbed areas shall be covered and/or mulched within 12 hours, if they are to remain unworked for more than 2 days. (7 days from May 1 to Sept. 30)
- Areas not being worked for 30 days or more shall be vegetated, unless the County determines that winter weather makes vegetation establishment infeasible. If this is the case, it must still be more permanently stabilized, using methods such as bonded fiber matrix, or other more stable BMPs.
- Slopes and stockpiles 3H:1V or steeper and more than 10 feet of vertical relief shall be covered if they are unworked for more than 12 hours.
- All areas not being worked prior to October 1, and are being seeded, shall be seeded by September 23. Mulching is required to protect all seeded areas until an adequate growth is established.
- Areas that are being hydroseeded shall have a tackifier mixed into the hydroseed to help stabilize mixture onto the soil.
- Enough cover material to sufficiently protect all disturbed areas shall be stockpiled on the site at the beginning of the wet season.
Perimeter protection
- Perimeter protection to filter sediment for sheetwash shall be located downslope of all disturbed areas and properly installed prior to upslope grading.
- 50 linear feet of silt fence per acre and the necessary stakes to hold the fence in place shall be stockpiled on-site.
- Phasing and more conservative Best Management Practices must be evaluated for construction activities near surface waters.
- Surface water controls are required unless no off-site discharge is anticipated for the specified design flow.
- Unsurfaced driveway entrances, access roads and parking areas used by construction traffic will be stabilized to minimize erosion and prevent tracking mud.
- Stabilized construction entrances will be installed as the first step of clearing and grading.
- Construction entrances will be set up so that all traffic leaving a job site is required to travel the entire length of entrance.
- Roads and parking areas will be stabilized immediately after the initial grading.
- Construction entrances will 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.
- Any sediment that is tracked onto pavement will be removed immediately by sweeping. The sediment collected by sweeping shall be removed or stabilized on-site.
- If non-vactor type sweepers are used, the deposition of these sweepers must be removed from sidewalks and gutters. The sediment collected by sweeping shall be removed or stabilized on-site.
- The pavement shall not be cleaned by washing/flushing streets.
- Sediment retention is required unless no off-site discharge is anticipated for the specified design flow.
- Sediment retention facilities will be installed before grading.
- If sediment retention facilities need to be removed for grading, additional ponds/traps/systems to accommodate storage capacity need to be installed on site. This will be done prior to removal of existing facility.
- Catch basin inserts are to be used to prevent sediments from entering drainage system. Inserts are to be inspected and cleaned weekly and after each rainfall event.
- Catch basins need to be checked for build up of sediments. If dead-storage (area between pipe invert and bottom of basin) is 1/3 or more filled with sediments, they are to be cleaned out and sediments removed or stabilized on-site.
- Dust is to be controlled on construction site.
- If water truck is used to to control dust on dirt/graded areas only.
- Water truck will only drop enough water to control the dust or reach the optimum moisture content of the soil for compaction. No run-off is to be generated.
- Controlling dust on paved roadways will be done by use of sweeper with water-jet sprayers. Only enough water should be applied to control dust while sweeping, while not generating run-off from sprayers that runs into catchbasins.
- All large projects will have a designated ESC supervisor who will be responsible for ESC review, maintenance and compliance.
- ESC will be inspected a minimum of once a week during the wet season and within 24 hours of significant storms (.5 inches/24 hour, or where run-off is generated).
- The ESC supervisor must be available, 24 hours, for rapid response to ESC problems and emergencies.
- A 24-hour phone number for the ESC Supervisor will be posted in a clearly visible location on the project site.
See Final Stabilization Standards (PDF*, 16KB).
Prior to final construction approval, the following conditions must be met:
- All disturbed areas of the site will be vegetated or otherwise permanently stabilized.
- Structural measures such as silt fence, slope drains, etc. will be removed from site.
- All permanent surface water facilities including catch basins, pipes, etc. will be cleaned.
- Any off-site catch basins that required protection will also be cleaned.
- If only the infrastructure of the site has been developed such as short plats and subdivisions, with building construction to occur under a different permit, then the critical area buffers, tracts, and setbacks will be clearly marked.
DDES inspection staff are available to answer any questions you may have about erosion and sediment control and wet season stabilization measures for permitted activities in unincorporated King County. For more information, please contact DDES customer service at 206-296-6600 and ask to speak with the inspector assigned to the specific project you're interested in.
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