Washington County, WI Environmental Rules: Stormwater Management (2026)

Section 238-8 of the Code of Washington County sets the performance standards a stormwater management plan must meet before a qualifying land development project can proceed. Under § 238-6B, the stormwater management requirements apply to activities such as subdivision plats, new public or private roadway construction, projects adding 20,000 square feet or more of new impervious surface, or any activity disturbing one acre or more of land.

The plan's peak-discharge standard, § 238-8A(1)(b), requires that calculated post-development peak stormwater discharge rates not exceed calculated predevelopment rates for the one-, two-, ten-, and 100-year, twenty-four-hour design storms, protecting downstream channels and conveyance systems from increased flows. The water-quality standard, § 238-8A(1)(c), requires new land development and infill projects to cut total suspended solids by 80% compared to no controls, while redevelopment projects need only a 40% reduction from parking areas and roads; agricultural production areas are exempt. The chapter also sets infiltration performance standards keyed to a site's percentage of connected impervious surface, and requires protective areas next to lakes, streams and wetlands, generally 50 to 75 feet wide, to be kept free of impervious surfaces except for structures authorized under shoreland or floodplain zoning.

The Land Conservation Committee, acting through the Land and Water Conservation Division of the Planning and Parks Department, reviews plans and issues permits under § 238-9, and enforces the chapter under § 238-15 with forfeitures, stop-work orders, permit revocation and emergency action.