Washington County, MN Environmental Rules: Erosion Control (2026)

Section 10.4 of the county's Development Code, Chapter Three (Subdivision Regulations), governs erosion control during construction in the unincorporated areas and townships the county regulates directly. Erosion control must follow the recommended practices of the Washington Conservation District and the applicable Watershed Management Organization, and all Best Management Practices must be consistent with the Minnesota Construction Site Erosion and Sediment Control Planning handbook.

The rules apply to construction activities producing runoff that leaves the site. Channelized runoff from adjacent areas passing through a site must be diverted around disturbed areas where practical; sheetflow runoff from adjacent areas over 10,000 square feet must be diverted unless shown to produce resultant runoff of less than 0.5 feet per second across the disturbed area for the one-year storm. Grading must proceed in a logical sequence to minimize exposed bare soil, and the limits of grading must be shown on the erosion control plan. Any disturbed ground left inactive 14 or more days must be stabilized by seeding or sodding (before September 15) or by mulching, covering, or an equivalent control measure.

Sites disturbing more than 10 acres at one time, or where a channel originates in the disturbed area, need one or more sedimentation basins with a surface area of at least 1 percent of the drainage area and at least 3 feet of depth, with sediment removed to maintain that 3-foot depth. Sites disturbing less than 10 acres at one time must instead use silt fences, straw bales, or equivalent measures along sideslope and downslope edges, with a required maintenance and inspection schedule. Soil storage piles holding more than 10 cubic yards must sit at least 25 feet from a roadway or drainage channel; piles remaining more than 7 days must be stabilized with mulch, vegetative cover, or tarps, while shorter-duration piles need straw bales or silt fence barriers. In-street utility repair or construction soil piles closer than 25 feet to a roadway or drainage channel must be tarped if exposed more than 7 days, and storm drain inlets must be protected with straw bales or comparable filtering barriers.