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King County has updated the Surface Water Design Manual (SWDM) and the Stormwater Pollution Prevention Manual (SPPM) to improve the clarity and effectiveness of the requirements and to comply with King County’s Phase 1 NPDES Permit which requires equivalency with the State’s 2019 Stormwater Management Manual for Western Washington. The SWDM contains the King County surface water and stormwater design and analysis requirements, procedures, and guidance for development applications in unincorporated King County. The SPPM presents source control best management practices for pollution prevention, as they are widely recognized as the least costly and most efficient and effective means of protecting and improving the quality and beneficial uses of water resources.