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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.


Urbanized Area Outfall Maps

Under the NPDES Phase II Permit, MDOT is required to develop maps identifying the locations of their known outfalls. While this is an ongoing effort, MDOT initially used two methodologies to locate outfalls in urbanized areas:

  • Using existing survey data to estimate outfall locations
  • Using Illicit Discharge Elimination Program investigations to estimate outfall locations.


Maps by MDOT Region

Bay Region Outfall Maps 
Grand Region Outfall Maps 
Metro Region Outfall Maps 
North Region Outfall Maps
Southwest Region Outfall Maps 
Superior Region Outfall Maps 
University Region Outfall Maps 
Dry Weather Screening Investigation Maps



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 or receiving water body that is not entirely composed of stormwater and/or not permitted by MDOT.

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.


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 (spills while topping off at gas stations, oil leaks on pavement, etc.) 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.

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).

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.