Stormwater runoff is a leading source of water pollution. Common pollutants in runoff include sediment, pathogens, salt, fertilizers, metals, oils, pesticides and litter. Increased stormwater runoff can impact surface waters such as rivers, lakes and streams through water level fluctuations, erosion of banks and vegetation changes, which in may turn cause or contribute to poor water quality.
Polluted stormwater contributes to beach closings, fish-eating advisories, excess algae growth and poor water clarity, especially in urban lakes.
Municipal Separate Storm Sewer System (MS4)
A municipal separate storm sewer system (MS4) is a system of conveyances (roads with drainage systems, municipal streets, curbs, gutters, ditches, man-made channels, storm drains) that is owned or operated by a public body, such as a county, city, or township. A storm sewer system is not connected with a wastewater treatment system. Stormwater, and the pollutants traveling with it, go directly through the storm sewer into nearby surface water.
The Minnesota Pollution Control Agency implements a stormwater program for municipal separate storm sewer systems (MS4s). The purpose of the stormwater program is to reduce the amount of sediment and pollution that enters surface water from storm sewer systems to the maximum extent practicable. Stormwater discharges associated with these storm sewer systems are regulated through a National Pollutant Discharge Elimination System Permit (NPDES). The primary goal of the permit is to improve water quality by reducing pollutants in stormwater discharges.
Dakota County holds a National Pollutant Discharge Elimination System Permit (NPDES) as a municipal separate storm sewer system. The permit requires Dakota County to develop a stormwater pollution prevention program that incorporates best management practices. The permit also gives Dakota County approval to discharge stormwater to lakes, rivers and wetlands in Minnesota. As a permit-holder, Dakota County ensures proper management of stormwater discharges from County-owned or operated facilities and conveyances into waters of the state.