According to EPA’s National Water Quality Inventory: 2000 Report, prepared under Section 305(b) of the Clean Water Act, urban storm water runoff and discharges from storm sewers are a primary cause of impaired water quality in the United States. These sources contribute to 13 percent of impaired rivers and streams, 18 percent of impaired lakes, 55 percent of impaired ocean shorelines, and 32 percent of impaired estuaries.
Runoff from municipal areas contains a mixture of pollutants from parking lots, streets, rooftops, lawns, and other areas. These areas contribute heavy metals, pesticides, sediment, nutrients, bacteria, and oxygen-demanding organic waste. Although (MS4s) are efficient at conveying water to avoid flooding, they also transport polluted runoff directly into nearby lakes, rivers, and streams without the benefit of wastewater treatment or filtration by soil or vegetation.