Phase 1 of the U.S. Environmental Protection Agency's (EPA) stormwater program was promulgated in 1990 under the Clean Water Act (CWA). Phase 1 relies on National Pollutant Discharge Elimination System (NPDES) permit coverage to address stormwater runoff from incorporated places with a population of 100,000 or greater on the 1990 U.S. census, construction sites larger than five acres and certain industrial sectors.
The Stormwater Phase 2 Final Rule is the next step in EPA's effort to preserve, protect and improve the nation's water resources from polluted stormwater runoff. The Phase 2 program expands the Phase 1 program by requiring additional operators of Municipal Separate Storm Sewer Systems (MS4s) in urbanized areas and operators of small construction sites, through the use of NPDES permits, to implement programs and practices to control polluted stormwater runoff. Phase 2 is intended to further reduce adverse impacts to water quality and aquatic habitat by instituting the use of controls on the unregulated sources of stormwater discharges that have the greatest likelihood of causing continued environmental degradation.
Stormwater discharges from MS4s in urbanized areas are a concern because of the high concentration of pollutants found in these discharges. Concentrated development in urbanized areas substantially increase 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. When left uncontrolled, these discharges can result in fish kills, the destruction of spawning and wildlife habitats, a loss in aesthetic value and contamination of drinking water supplies and recreational waterways that can threaten public health.
Polluted storm water runoff is often transported to MS4s and ultimately discharged into local rivers and streams without treatment. EPA's Stormwater Phase 2 Rule establishes a MS4 stormwater management program that is intended to improve the Nation's waterways by reducing the quantity of pollutants that stormwater picks up and carries into storm sewer systems during storm events. Common pollutants include oil and grease from roadways, pesticides from lawns, sediment from construction sites and carelessly discarded trash, such as cigarette butts, paper wrappers and plastic bottles. When deposited into nearby waterways through MS4 discharges, these pollutants can impair the waterways, thereby discouraging recreational use of the resource, contaminating drinking water supplies and interfering with the habitat for fish, other aquatic organisms and wildlife.