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stable driving surface and to stabilize any areas that have eroded. <br />Following construction, these areas shall be restored to pre -construction <br />condition or better to prevent future erosion. <br />Perform street cleaning at the end of each day or more often if necessary. <br />BMP C120: Temporary and Permanent Seeding <br />Purpose Seeding reduces erosion by stabilizing exposed soils. A well -established <br />vegetative cover is one of the most effective methods of reducing erosion. <br />Conditions of Use Use seeding throughout the project on disturbed areas that have reached <br />final grade or that will remain unworked for more than 30 days. <br />The optimum seeding windows for western Washington are April 1 <br />through June 30 and September 1 through October 1. <br />Between July 1 and August 30 seeding requires irrigation until 75 percent <br />grass cover is established. <br />Between October 1 and March 30 seeding requires a cover of mulch with <br />straw or an erosion control blanket until 75 percent grass cover is <br />established. <br />Review all disturbed areas in late August to early September and complete <br />all seeding by the end of September. Otherwise, vegetation will not <br />establish itself enough to provide more than average protection. <br />• Mulch is required at all times for seeding because it protects seeds <br />from heat, moisture loss, and transport due to runoff. Mulch can be <br />applied on top of the seed or simultaneously by hydroseeding. See <br />BMP C121: Mulching for specifications. <br />Seed and mulch, all disturbed areas not otherwise vegetated at final <br />site stabilization. Final stabilization means the completion of all soil <br />disturbing activities at the site and the establishment of a permanent <br />vegetative cover, or equivalent permanent stabilization measures (such <br />as pavement, riprap, gabions, or geotextiles) which will prevent <br />erosion. <br />Design and Seed retention/detention ponds as required. <br />Installation Install channels intended for vegetation before starting major <br />Specifications earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated <br />channels that will have high flows, install erosion control blankets <br />over hydroseed. Before allowing water to flow in vegetated <br />channels, establish 75 percent vegetation cover. If vegetated <br />channels cannot be established by seed before water flow; install sod <br />in the channel bottom —over hydromulch and erosion control <br />blankets. <br />Volume 11— Construction Stormwater Pollution Prevention - December 2014 <br />4-13 <br />