This image shows a person collecting a water sample from an outfall
Image of a person collecting a water sample from an outfall


Our storm sewer systems carry water directly to our lakes, rivers, and wetlands without additional treatment, so to prevent pollution from entering our surface water, only clean stormwater should enter a storm sewer system. If any other discharge enters the system, it is usually an illicit discharge. Minimum Control Measure (MCM) 3 of the MS4 General Permit requires permittees to develop and implement a program to detect and eliminate illicit discharges within their storm sewer system.

MS4 General Permit requirements for MCM 3

The illicit discharge detection and elimination (IDDE) program must include:

  • A map of the MS4 that includes all pipes 12 inches or greater and their flow direction; outfalls, including the unique identifier and geographic coordinates; municipally owned or operated structural stormwater best management practices (BMPs); and all receiving waters.
  • A regulatory mechanism to prohibit illicit discharges.
  • The incorporation of illicit discharge detection into all municipal operation inspection and maintenance activities, such as those conducted on ponds, outfalls, and other structural stormwater BMPs. These inspections should be conducted during dry weather, when possible.
  • Detecting and tracking the source of illicit discharges using visual inspections.
  • Training of all field staff on illicit discharge recognition.
  • Identifying priority areas likely to have illicit discharges by evaluating land uses associated with business and industrial activities, areas where illicit discharges have been observed in the past, areas with storage of large quantities of materials that could result in an illicit discharge. These locations should have additional illicit discharge inspections.
  • Procedures for investigating, locating, and eliminating the source of illicit discharges.
  • Spill response procedures. These procedures must include the requirement to notify the Minnesota Duty Officer.
  • Enforcement Response Procedures to compel compliance with the illicit discharge prohibition regulatory mechanism.
  • Documentation as required here.


Click on the blue links above in the "MS4 General Permit requirements" section to get more information and resources specific to those permit requirements. In addition, all resources related to MCM 3 are below.

Fact sheets and guidance documents

Model language

Documentation and tracking templates

Example procedures

Training tools