Renton, WA Environmental Rules: Stormwater Management (2026)

Renton Municipal Code 4-6-030 adopts the King County Surface Water Design Manual (SWDM) and the city Amendments as its stormwater standard under its NPDES Phase II permit issued by Washington Department of Ecology. Any development project that creates or replaces 2,000 square feet or more of impervious surface, clears more than 7,000 square feet of vegetation, or disturbs more than 1 acre must comply with SWDM Core Requirements including on-site stormwater BMPs, flow control, water quality treatment, erosion control, and operation and maintenance plans. Single-family residential projects often fall under Small Project drainage review with simpler BMPs such as full dispersion, rain gardens, or permeable pavement. Larger projects require full drainage review and detention facilities. Illicit discharge to storm drains is prohibited under RMC 4-6-030, including car wash water, paint, concrete wash, and other pollutants that could reach the Cedar River or Lake Washington. Properties within the Cedar River shoreline, Black River Riparian Forest, or wetland buffers face heightened stormwater review. Report spills to the city at (425) 430-7400.