Illicit discharges are generally any discharge into a storm drain system that is not composed entirely of stormwater. The exceptions include water from fire fighting activities and discharges from facilities already under an NPDES permit. Illicit discharges are a problem because, unlike wastewater which flows to a wastewater treatment plant, stormwater generally flows to waterways without any additional treatment. Illicit discharges often include pathogens, nutrients, surfactants, and various toxic pollutants.
Phase II MS4 entities are required to develop programs to detect and eliminate illicit discharges. This primarily includes developing:
An effective illicit discharge program needs to be both reactive and proactive. The programs are reactive in addressing spills and other illicit discharges to the storm drain system that are found. These programs must also be proactive in preventing and eliminating illicit discharges through education, training and enforcement.