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    State of Washington (Western)

    Excerpt from Executive Summary of 2019 Revisions:

    "The Stormwater Management Manual for Western Washington (SWMMWW) provides guidance on the measures necessary to control the quantity and quality of stormwater. Local municipalities use this manual to set stormwater requirements for new development and redevelopment projects. Land developers and development engineers use this manual to design permanent stormwater control plans, create construction stormwater pollution prevention plans, and determine stormwater infrastructure. Businesses use this manual to help design their stormwater pollution prevention plans.

    The greatest use of the 2005 SWMMWW has been through National Pollutant Discharge Elimination System (NPDES) stormwater permits. The Municipal Stormwater General Permits for western Washington incorporate and reference the SWMMWW. The Industrial Stormwater General Permit, Construction Stormwater General Permit, Boatyard General Permit, and the Sand and Gravel General Permit reference the SWMMWW. Since 2005, Ecology has reissued or issued for the first time all of these NPDES stormwater permits. The 2012 revisions to the SWMMWW will help permittees comply with these permits.

    The method by which this manual controls the adverse impacts from quality and quantity of stormwater is primarily through the application of Best Management Practices. Ecology has revised many of the BMPs from the 2005 SWMMWW to improve their effectiveness for protecting water quality and to meet the intent of the anti-degradation provisions of the water quality standards.

    In addition, Ecology revised this manual to include low impact development (LID) related definitions, requirements, and an LID performance standard. Ecology made the LID revisions based on rulings by the Pollution Control Hearings Board, after consulting with LID advisory committees, and after providing opportunities for public input. The manual update also supports the new LID requirements in the Western Washington Municipal Stormwater Permits.

    Other major changes include revised guidelines on protecting wetlands and designing infiltration facilities, and numerous minor revisions for clarity."


    Stormwater Management Manual for Western Washington (2019)


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