The Federal Water Pollution Control Act, more commonly called the Clean Water Act, prohibits the discharge of pollutants from a point source to waters of the United States without a National Pollution Discharge Elimination System (NPDES) permit. In 1990 the U.S. Environmental Protection Agency (EPA) specifically applied the NPDES permit requirement to stormwater discharges from 11 industrial sectors. There are two types of NPDES permits: general and individual. A general permit imposes nearly identical requirements on permit holders and the application process is nearly automatic.
The EPA has delegated permitting authority to most states, thus EPA only issues NPDES permits in states that do not have authority to administer the NPDES program (Idaho, Massachusetts, New Hampshire and New Mexico). EPA regulates industrial stormwater discharges under its Multi-Sector General Permit (MSGP). Many states similarly permit industrial stormwater under one general permit, though some states issue industry sector-specific general permits. Industrial facilities rarely apply for individual permits for stormwater discharges, but the permitting authority may elect to transfer a facility to an individual permit to increase regulatory oversight.
While the specific components of general permits vary from state to state, there are some important common features. General industrial permits require the facility owner or operator submit and implement a Stormwater Pollution Prevention Plan (SWPPP) that describes operational, structural and treatment best management practices (BMPs) that minimize stormwater pollution. Many industrial permits also set forth numeric “benchmark” water quality concentrations to help facilities measure their BMPs’ efficacy, and require facilities to monitor and report effluent pollutant concentrations. While benchmarks are not enforceable effluent limits, some permits do require active responses to benchmark excursions. EPA has established additional enforceable, technology-based effluent limitations for stormwater associated with certain industrial activities.