![]() In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. ![]() The duff layer and native topsoil should be retained in an undisturbed state to the maximum extent practicable. Soil organic matter can be attained through numerous materials such as compost, composted woody material, biosolids, and forest product residuals.Establishing a minimum soil quality and depth will provide improved onsite management of stormwater flow and water quality.These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod. Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water infiltration nutrient, sediment, and pollutant adsorption sediment and pollutant biofiltration water interflow storage and transmission and pollutant decomposition.Key points of BMP T5.13, including the use of compost, are outlined below: TOPSOIL DEPTH PLANTING XSECTION SEATTLE MANUALSince its initial publication, local governments in western Washington (west of the Cascade Mountains) have been required to use this state manual to implement regulations that comply with state water quality goals/standards. This stormwater manual serves as the main reference document from which local jurisdictions must base amendments of their codes. “ BMP T5.13, Post-Construction Soil Quality and Depth,” found in Washington State Department of Ecology’s Stormwater Management Manual for Western Washington (Volume V: Runoff Treatment BMP’s, Chapter 5, BMP T5.13) is the guideline driving soil policy change. Recognizing the connection between degraded watersheds and soil health, the state of Washington adopted BMPs suggested by Soils for Salmon in the early 2000s. ![]() Such methods, like amending soil with compost, help restore soil ecosystems and maintain microbiological life that are integral components to the region’s economic and environmental well-being. The program drives landscapers, builders, developers, and citizens to use low impact development (LID) BMPs, that reduce stormwater runoff and pollution, while limiting water usage demands. Developed by the Washington Organic Recycling Council (WORC), the program was founded in 1999 to protect Western Washington’s Puget Sound by educating the public about the soil to water connection. Soils for Salmon is an initiative established to promote guidelines, best management practices (BMPs), and policy change in an effort to preserve the overall environmental health of waterways in Washington State. ![]()
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