Polluted storm water runoff is often transported to municipal separate storm sewer systems (MS4s) and ultimately discharged into local rivers and streams without treatment. The Environmental Protection Agency (EPA) Storm Water Phase II Rule establishes an MS4 Storm Water management program that is intended to improve the Nation’s waterways by reducing the quantity of pollutants that Storm Water 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
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.
National Pollutant Discharge Elimination System
In 1990, EPA promulgated rules establishing Phase I of the National Pollutant Discharge Elimination System (NPDES) Storm Water program. The Phase I program for MS4s requires operators of “medium” and “large” MS4s, that is, those that generally serve populations of 100,000 or greater, to implement a Storm Water management program as a means to control polluted discharges from these MS4s. The Storm Water Phase II Rule extends coverage of the NPDES Storm Water program to certain “small” MS4s but takes a slightly different approach to how the Storm Water management program is developed and implemented.