What is the National Pollutant Discharge Elimination System (NPDES) Storm Water Program?
Polluted storm water runoff is a leading cause of impairment to the nearly 40 percent of surveyed U.S. water bodies which do not meet water quality standards. Over land or via storm sewer systems, polluted runoff is discharged, often untreated, directly into local water bodies. When left uncontrolled, this water pollution can result in the destruction of fish, wildlife, and aquatic life habitats; a loss in aesthetic value; and threats to public health due to contaminated food, drinking water supplies, and recreational waterways.

Mandated by Congress under the Clean Water Act in 1987, the NPDES Storm Water Program is a comprehensive two-phased national program for addressing the non-agricultural sources of storm water discharges that adversely affect the quality of our nation's waters. The Program uses the National Pollutant Discharge Elimination System (NPDES) permitting mechanism to require the implementation of controls designed to prevent harmful pollutants from being washed by storm water runoff into local water bodies.

The Phase I Rule of the NPDES Program established in 1990, addressed priority pollutant sources, including cities with populations over 100,000, construction sites larger than 5 acres, and certain industrial sources.

In 1999, Phase II went into effect. It requires NPDES permit coverage for storm water discharges from cities with populations over 10,000 that are not in a metropolitan planning area and cities that are less than 10,000 if they are in a metropolitan planning area.