Since the passage of the Clean Water Act (CWA) in 1972, the quality of our Nation’s waters has improved dramatically. Despite this progress, however, degraded waterbodies still exist. According to the 2000 National Water Quality Inventory, a biennial summary of State surveys of water quality, approximately 40 percent of surveyed U.S. waterbodies (waters of the United States) are impaired by pollution and did not meet water quality standards. A leading source of this impairment is polluted stormwater runoff from urban and suburban areas.
Concentrated development in urbanized areas substantially increases impervious surfaces, such as city streets, driveways, parking lots, and sidewalks, on which pollutants from concentrated human activities settle and remain until a storm event washes them into nearby storm drains. Common pollutants include pesticides, fertilizers, oils, salt, litter and other debris, and sediment. Another concern is the possible illicit connections of sanitary sewers, which can result in fecal coliform bacteria entering the storm sewer system. Stormwater runoff picks up and transports these and other harmful pollutants then discharges them – untreated – to waterways via storm sewer systems.
In 1987, Congress directed the Environmental Protection Agency (EPA) to develop a regulatory program to address stormwater pollution. In response, EPA issued regulations in 1990 authorizing the creation of a permitting approach under the National Pollutant Discharge Elimination System (NPDES). Specific polluting sources were targeted by the EPA in a two-phase approach (Phase I and Phase II).
In December 2002, the State of Arizona's Department of Environmental Quality (ADEQ) took primacy of the NPDES program in Arizona (except for Indian Tribal lands) under the Arizona Discharge Elimination System (AZPDES) program.
Environmental Protection Agency: Storm Water Phase II Final Rule, an Overview, Fact Sheet Series, EPA 833-F-00-001, January 2000 (revised December 2005).