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Illicit Discharge Detection and Elimination Program Development

Minimum Measure: Illicit Discharge Detection and Elimination

Subcategory: Developing an IDDE Program

Photo Description: Illicit discharges are prevalent in urban areas, especially in industrial and commercial areas, such as this incident where mop water was dumped in a parking lot behind a motel.
Illicit discharges are prevalent in urban areas, especially in industrial and commercial areas, such as this incident where mop water was dumped in a parking lot behind a motel.

Stormwater regulations define an "illicit discharge" as "any discharge to a municipal separate storm sewer that is not composed entirely of stormwater" (except discharges resulting from fire fighting activities and a few other categories). Common sources of non-stormwater, dry weather discharges in urban areas include apartments and homes, car washes, restaurants, airports, landfills, and gas stations, to name but a few. These so called "generating sites" discharge sanitary wastewater, septic system effluent, vehicle wash water, washdown from grease traps, motor oil, antifreeze, gasoline and fuel spills, among other substances. Although these illicit discharges can enter the storm drain system in various ways, they generally result from either direct connections (e.g., wastewater piping either mistakenly or deliberately connected to the storm drains) or indirect connections (e.g., infiltration into the storm drain system, spills, or "midnight dumping"). Illicit discharges can be further divided into those discharging continuously and those discharging intermittently.

Studies indicate that dry weather discharges contribute significant pollutants to receiving waters. The detection and elimination of illicit discharges is important to protect and restore urban waterways. The development of an effective municipal illicit discharge detection and elimination (IDDE) program requires the establishment of adequate legal authority to prohibit illicit discharges; to assess and prioritize potential areas, pollutants, or behaviors of concern; to coordinate existing resources; to establish a mechanism to track activities; and to establish measurable goals.


Sources of illicit discharges in urban areas are numerous and seemingly ever-present. All urban municipalities can benefit from establishing a comprehensive program to address these non-stormwater discharges, including reporting hotlines and response procedures. Establishing a strong municipal program with clear policies and procedures will ensure that individual incidents are addressed consistently. It will also help establish evidence in cases where discharges result from criminal negligence.

Municipalities with older infrastructure should concentrate on illicit connections to the storm drain system. This is because recordkeeping and code enforcement may have been lacking when residences and businesses were first built, and undocumented modifications might have been made in the meantime. Municipalities with older neighborhoods should prioritize areas for targeted investigation, such as through dry weather screening at outfalls. Older parts of the storm drain system may also be deteriorating and require repair or replacement.


According to Brown et al. (2004) in IDDE: A Guidance Manual for Program Development and Technical Assessments, four steps are recommended for the development of an effective IDDE program:

  1. Audit Existing Resources and Programs: It is important to identify the most appropriate and capable agencies and staff to administer and implement an IDDE program early in the process. Gaps in resources or manpower should be noted and addressed as the program is developed. A comprehensive self-audit is recommended to determine the effectiveness and efficiency of existing programs. A self-audit should address and research existing sewer infrastructure (storm and sanitary), legal authority, mapping and geographic information system (GIS) resources, as well as field and laboratory staff and equipment. Available educational and emergency response resources should be assessed as well. And, of course, financial resources and fiscal planning requirements must be reviewed. The audit should not focus solely on "in-house" resources. It should also explore the possibility of integrating resources from neighboring jurisdictions, co-permittees, non-profit organizations and volunteers, and other agencies.

  2. Establish Responsibility, Authority, and Tracking: To implement an effective IDDE program, three primary questions must be answered early in the process:

    • Who will be responsible for administration?
    • On what legal authority?
    • How will detected discharges and follow up elimination activities be tracked?

    Based on the self-audit, determine the most capable agency or department to administer the program. Is the public works department, for example, equipped and authorized to run the program? Local ordinances may need to be amended or developed to implement and enforce an IDDE program. In general, an IDDE ordinance should prohibit illicit discharges, provide the authority to investigate suspected discharges, and define the enforcement tools necessary to require responsible parties to eliminate the discharges. This authority may be available in an existing stormwater ordinance, in building or health codes, or in a combination of all three.

    A tracking system is important because it allows the program administrator to track illicit discharges and follow up activities, and to measure progress toward program goals. The tracking system could be incorporated into an existing system (i.e., GIS system, spill response, citizen complaints) or developed expressly for the IDDE program. Ideally, the tracking system would be part of a broader stormwater GIS system that would allow for geospatial analysis of trends in illicit discharge activity. The tracking system should be developed early in the process to allow managers to more effectively evaluate and report progress.

  3. Complete a Desktop Assessment of Illicit Discharge Potential: Many municipalities have finite resources for detecting and eliminating illicit discharges. To develop the most cost-effective and efficient IDDE program, it is important to prioritize areas within a community for investigation. The Center for Watershed Protection (CWP) has developed a "desktop assessment method" to rapidly determine the potential severity of illicit discharges in various areas throughout a community or watershed. The method has five elements:

    1. Watershed delineation
    2. Data and mapping compilation
    3. Derivation of discharge screening factors
    4. Screening and ranking of areas based on these factors
    5. Mapping priority locations for field investigations

    Refer to the Guidance for a more detailed explanation of the process. The effectiveness of an assessment will vary based on what data are available.

  4. Develop Program Goals and Implementation Strategies: After completing the audit and desktop assessment, it is critical that a program manager develop achievable, measurable IDDE goals. The stormwater manager should now have a basic understanding of community water quality issues, how and in what areas IDDE may be impacting receiving waters, and the resources available to eliminate the discharges. This information should be used to set measurable goals and strategies to achieve those goals. Detailed implementation strategies should be documented in standard operating procedures (SOPs) to ensure management and field staff are aware of procedures, reporting requirements, contact staff, and schedules. Over time, goals should be reassessed based on progress and changing water quality or community conditions.
Case Study

In 1987, Wayne County, Michigan, developed an IDDE program Exit EPA Site. Wayne County encompasses 33 cities and 10 townships in Southeast Michigan, including Detroit. Based on 17 years of experience, Wayne County has found that an effective approach to the elimination of illicit discharges to surface waters combines focused attention on areas with known water quality problems with site visits to facilities. Wayne County's illicit discharge program is based on four main elements:

  1. Choosing an area for investigation
  2. Developing a facility inventory
  3. Conducting site visits and inspections
  4. Following up with education and enforcement actions

To choose which areas to investigate, the County developed a prioritization scheme based on the following factors:

  • Outfall size, used as a proxy for drainage area
  • Water quality monitoring data that identify hot spots for bacteria and other pollutants
  • History of complaints indicating frequent or continuous discharges
  • Generalized land use (focusing on commercial and industrial areas)
  • Number of hazardous waste-generating businesses, and businesses on Michigan's Critical Materials Register
  • Number of Priority I commercial/industrial facilities, which include automobile-related businesses and heavy manufacturing facilities. Of lesser priority (priority II) are printers, dry cleaners and laundries, photo processors, utilities, paint stores, water conditioners, chemical laboratories, construction companies, and medium-light manufacturing. Priority III facilities include other industrial facilities, private service agencies, retail establishments, and schools.

The County then uses GIS to score subwatersheds or investigative areas by the number of priority I and II businesses present. The application also creates a business list for a selected geographical area and coordinates these data with a tracking database.

Once areas are ranked, the county conducts surveys of businesses. The surveys consist of a visual inspection of the business, discussions with the facility operator, placing dye in plumbing fixtures, flushing the dye, observing it in sewers outside the building and reporting the findings to the owner. The illicit discharge teams also investigate complaints of suspicious materials reported dumped into drains, and sample outfalls to search for illicit discharges. The parameters sampled depend on visual and odor evaluations of the discharge. A GPS coordinate is identified for the outfall and samples are taken.

Between the program's inception in 1987 and December 2003, 5,753 facilities were inspected, and 1,483 illicit connections were found at 417 facilities. Approximately 7 percent of the inspected facilities had illicit connections, and those facilities with illicit connections tended to have more than one (an average of 3 to 4 illicit connections per facility). Wayne County estimates that the program annually prevents more than 12.5 million gallons of polluted water and 1 million pounds of polluting material from entering Wayne County surface waters.

As part of the Rouge River National Wet Weather Demonstration Project, Wayne County has developed guidance and numerous publications that detail its program and describe lessons learned in developing and implementing an illicit discharge program.


Brown, E., D. Caraco, and R. Pitt. 2004. Illicit Discharge Detection and Elimination: A Guidance Manual for Program Development and Technical Assessments. Center for Watershed Protection, Ellicott City, MD. []

USEPA Case Study, 2004. Focus on Commercial and Industrial Site Visits: Wayne County, Michigan. [] Last updated November 12, 2004. Accessed March 3, 2006.


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Last updated on June 01, 2006