Illicit Discharges

Illicit Discharge Detection and Elimination (IDDE) is a component of the Phase II Stormwater Regulations. It is the third minimum control measure (MCM). The regulated municipalities in the coalition have worked together to map their outfalls that discharge stormwater to local waterbodies. The GPS locations of these outfalls have been incorporated into GIS software. In addition to mapping their outfalls, the municipalities have also passed local laws prohibiting illicit discharges to their stormwater conveyance systems and local waterbodies.

What is an illicit discharge?

An illicit discharge is any discharge to a stormwater conveyance system, stream, river, lake, or other waterbody that is not composed entirely of stormwater. An illicit discharge could result from the following:

  • Dumping automobile oil or another pollutant (gasoline, paint, sewage etc) into a stormwater conveyance system (catch basin, ditch) or directly into a waterbody.
  • An illicit connection to the stormwater conveyance system, such as a sewer pipe or shop floor drain connected to the stormwater conveyance system.
  • A pipe that bypasses the sanitary sewer connection or septic drainfield and directly discharges to the stormwater conveyance system (ditch, open channel) or waterbody.
  • Indirectly through stormwater runoff. For example, sediment being picked up by rainwater and moving offsite to the stormwater conveyance system or local waterbody.
  • Indirectly through an old and damaged sanitary sewer line that is leaking fluids into a cracked storm sewer line or a failing septic system that is leaking into a crack storm sewer line or causing a surface discharge into the stormwater conveyance system.
Figure 1: An illicit discharge of sediment from a construction site.

Figure 1: An illicit discharge of sediment from a construction site.

What are the hazards of illicit discharges?

Illicit discharges can contribute high levels of pollutants to waterbodies. Common pollutants found in illicit discharges include: raw sewage (bacteria, viruses), heavy metals, oil/grease, solvents, and nutrients. EPA studies have shown that pollutant levels in these discharges are high enough to significantly degrade water quality, close beaches, and negatively impact aquatic, wildlife, and human health.

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