The Clean Water Act of 1972 established a basic structure for regulating discharges of pollutants into the waters of the United States. It initiated a national commitment to restore and maintain the chemical, physical, and biological integrity of the nation's waters.

In Phase I of the Clean Water Act, the EPA focused mainly on the chemical aspect. At the beginning of the Act's implementation, efforts focused on regulating discharges from industrial facilities. Many of those issues have mechanisms in place to protect our nation’s water. However, even after over 30 years of regulation, water pollution is still a problem in the U.S.

In addition, Phase I established rules for the National Pollutant Discharge Elimination System (NPDES). During this phase, operators of medium or large Municipal Separate Storm Sewer Systems (MS4s) were required to implement a Stormwater management program. Later the Stormwater Phase II Rule extended this coverage to small MS4s.

During the past decade, the emphasis of the Clean Water Act has been directed to physical and biological integrity. This includes more attention being paid to nonpoint source pollution (NPS). NPS pollution comes from diffuse sources such as rainfall or snowmelt. This water is commonly referred to as Stormwater. As water runs over the ground, paved streets, parking lots, rooftops, and constructions sites, it picks up pollutants such as sediment, debris, and chemicals. Common pollutants include Sediment, Excess Nutrients, Oil and Grease, Heavy Metals, Bacteria, Toxic Substances, Organic Matter, and Litter.

Stormwater containing one or more of the above contaminants seeps into the ground and/or drains into storm sewers. Many people do not understand that the water that enters a storm drain does not go to a water treatment facility. Polluted Stormwater runoff is ultimately discharged into local rivers and streams without treatment.

The EPA’s Stormwater Phase II Rule establishes an MS4 Stormwater Management Practices (SWMP) 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. When deposited into nearby waterways through discharges, these pollutants impair waterways, contaminate drinking water supplies; interfere with the habitat for fish, aquatic organisms, and wildlife; thereby discouraging recreational use of this water resource.