Municipal Separate Storm Sewer System (MS4) boundaries in Minnesota

In general terms, MS4s are publicly owned or operated stormwater infrastructure, used solely for stormwater, and which are not part of a publicly owned wastewater treatment system. Examples of stormwater infrastructure include curbs, ditches, culverts, stormwater ponds and storm sewer pipes. <br/><br/>By federal rule, stormwater systems in urban areas are labeled Mandatory MS4s. By state rule, permit applicability is based on urbanized area as defined by the latest decennial census, population, and proximity to special receiving waters (e.g., trout streams, Outstanding Resource Value Waters, and impaired waters). In addition, Minnesota requires MS4s located at least partially within an urbanized area that have resident capacity, bed count, or average daily user population of 1,000 or more to obtain a permit. These are referred to as non-traditional MS4s. <br/><br/>MS4 owners must establish stormwater pollution prevention programs that include public education and involvement, illicit discharge elimination, construction-site runoff controls, and stormwater best management practices.<br/>