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Illicit Discharge

Steam cascading over rocks.
Department of Transportation

Illicit Discharge

As part of MDOT's Illicit Discharge Elimination Program (IDEP), employees are trained and educated to identify illicit connections or discharges to department's drainage system. The most common warning signs of illicit discharges are dry weather flow, suds, sewage, oil and gas. In addition, MDOT field crews investigate point source discharges (PSDs) as part of their dry weather screening component of IDEP. A PSD is an outfall from a drainage system to waters of the state, or a point where a stormwater drainage system discharges into a system operated by another public body.

IDEP Protocol Manual


Illicit discharge is any discharge (or seepage) to the separate stormwater drainage system that is not composed entirely of stormwater or uncontaminated groundwater.

Illicit connection is any direct or indirect connection to the MDOT drainage system that is not entirely composed of stormwater and/or not permitted by MDOT.

Illicit Discharge Warning Signs

Usually recognized as a sheen on the water. Natural sheens are differentiated from oil & gas sheens by swirling the sheen around in the water. If it re-attaches, the sheen is oil and/or gas. Natural sheens will remain separated. Oil & gas enters waterbodies via stormwater runoff and illegal dumping.

Sanitary sewage may be present if there is black staining inside the drainage pipe or visible evidence of sanitary waste such as toilet paper or gray water.  Sewage may originate from septic tank overflow pipes or improperly dumped travel trailer waste. In some cases, a whiting event can be confused with an illicit sanitary discharge.

Foam in water can indicate pollution or be naturally occurring. Foam from illicit discharges can deplete oxygen levels in water. Improperly connected car washes or washing machines often result in foam at an outlet.

Dry weather flow is noted when it has not rained for at least 72 hours and the storm drain has flow or the drain shows signs of intermittent flow (staining, odor).

Report suspected illicit discharge* anonymously to the Pollution Emergency Alerting System (PEAS) hotline at:


Protect the quality of streams and public health, report illicit discharges.

*This includes dumping of waste/oil or other vehicle fluids and suspicious pipes outletting to ditches.