Storm Water regulations define an “illicit discharge” as “any discharge to a Municipal Separate Storm Sewer (MS4) that is not composed entirely of storm water” (except exempted discharges). Common sources of non-storm water, dry weather discharges in urban areas include:
- Apartments and homes
- Car washes
- Gas stations
These so-called “generating sites” may potentially discharge sanitary waste water, septic system effluent, vehicle wash water, wash down from grease traps, motor oil, antifreeze, gasoline and fuel spills, among other substances. Although these illicit discharges can enter the storm drain system in various ways, they generally result from either direct connections or indirect connections.
Studies indicate that dry weather discharges contribute significant pollutants to receiving waters. The detection and elimination of illicit discharges are important to protect and restore urban waterways.This minimum control measure of the Storm Water Management Program is designed to reduce pollutants in storm water runoff to receiving waters. It requires the development and implementation of a program to identify and eliminate sources of illicit discharge and illegal dumping.
You can learn more about illicit discharges from this fact sheet published by the EPA.