MCM 3: Illicit Discharge Detection & Elimination (IDDE)

Federal regulations define an illicit discharge as “any discharge to an MS4 that is not composed entirely of stormwater…” with some exceptions. Illicit discharges are considered “illicit” because MS4s are not designed to accept, treat, or discharge such non-stormwater wastes.

Sources of Illicit Discharges

Illicit discharges enter the system through either direct connections (e.g., wastewater piping either mistakenly or deliberately connected to the storm drains) or indirect connections (e.g., infiltration into the MS4 from leaking sanitary systems, spills collected by drain inlets, or paint or used oil dumped directly into a drain). Once an illicit discharge is identified and/or detected, the source should be eliminated.

Untreated discharges may contribute high levels of pollutants, including heavy metals, toxins, oil and grease, solvents, nutrients, viruses, and bacteria, to receiving water bodies.

Illegal Dumping Activities

Illegal dumping is a major cause of stormwater pollution. Public witness complaints provide the most immediate source of information. The following are indicators of possible illegal dumping or illicit discharges:

• Unusual color or cloudiness
• Algae
• Strong pungent or musty odor
• Dead vegetation or inhibited growth
• Floating debris
• Pipe corrosion
• Surface scum or foam
• Stains on channel bottom or sides
• Oil sheen
• Dead animals