HomeMy WebLinkAboutErosion Control Wet Season Requirements.pdf
EROSION CONTROL WET SEASON REQUIREMENTS
Sites with exposed soils during the WET SEASON (October 1 to April 30) shall be subject to special erosion control
provisions. These special provisions are required in addition to the standard TESC cover measures. All projects that clear,
grade or otherwise disturb the site, must provide erosion and sediment controls to the maximum extent possible, to
prevent the transport of sediment from the project site to downstream drainage facilities, water resources, and adjacent
properties.
The following provisions for wet season construction are detailed in Appendix D of the 2009 King County Surface Water
Manual. Please ensure your site is protected and complies with the special provisions outlined below. The basic
requirements are:
1. The allowed time that a disturbed area can remain unworked without cover measures is reduced to two (2) days,
rather than seven (7) days.
2. Stockpiles, steep cut, and fill slopes are to be covered or protected with mulch, sod, plastic covering, jute mat etc. if
left unworked for more than 12 hours.
3. Cover materials (plastic, matting, etc.) sufficient to cover all disturbed areas, shall be stockpiled and available on site.
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. Seeded should be completed by September 23.
5. Mulch is required to protect all seeded areas.
6. Fifty linear feet of silt fence (and the necessary stakes) per disturbed acre must be stockpiled on site.
7. Properly installed silt fencing is mandatory along the downslope of all disturbed areas of the site. Perimeter
protection filters runoff and reduces the amount of sediment that may leave the site.
8. Sediment retention is required unless no offsite discharge is anticipated for the specified design flow.
9. Construction road and parking lot stabilization are required for all sites unless the site is underlain by coarse-grained
soil.
10. Surface water controls are required unless no offsite discharge is anticipated for the specified design flow.
11. Phasing and more conservative BMPs must be evaluated for construction activity near surface waters.
12. Any runoff generated by dewatering shall be treated through construction of a sediment trap 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. A straw bale filter shall be placed around the discharge from the dewatering pump. If
there is not space for a sediment trap or 25 feet of suitable vegetation, other filtration methods shall be required.
13. The frequency of maintenance review should be increased from weekly to daily where warranted.