• In addition to industrial wastewater discharges, NPDES also applies to stormwater discharges from industrial facilities.

In addition to industrial wastewater discharges, the National Pollutant Discharge Elimination System (NPDES) also applies to stormwater discharges from industrial facilities. Facilities with the following types of stormwater discharges, among others, must apply for a NPDES permit:

• A discharge associated with industrial activity, including construction activities;
• A discharge from a large or medium municipal storm sewer system; or
• A discharge which the Environmental Protection Agency (EPA) or the state determines to contribute to a violation of a water quality standard or is a significant contributor of pollutants to waters of the United States.

Across the nation, many waterbodies are listed as impaired because of pollutants found in stormwater. These pollutants include sediment, pathogens, nutrients, and metals. If a waterbody is impaired, the state or federal EPA must set a Total Maximum Daily Load (TMDL) for a pollutant which identifies the total pollutant load the waterbody can handle before it cannot meet its water quality standards. Stormwater TMDLs are implemented through the NPDES stormwater permitting system. The program covers most municipalities and most construction activities.

Watersheds are affected by construction activities because land development converts natural areas into “impervious cover.” Blacktopped parking lots, buildings, streets, and other impervious surfaces prevent water from soaking into the ground or being taken up by plants. The more impervious cover an area has, the more stormwater runoff will find its way into nearby waterbodies. The increase in volume and rate of runoff can erode stream channels and transport more pollutants into streams, lakes, and other bodies of water. Industries and construction companies must meet specific effluent limits for stormwater runoff in their NPDES permits.