Illicit Connections and Illicit Discharges

From Beachapedia

Illicit Connection (Kent County, Michigan)
Correct Sewer Connection (Kent County, Michigan)

Despite the somewhat risqué title, the subject of this article is connections or discharges from sewer systems to stormdrain systems. When this happens, untreated sewage flows into streams, rivers, lakes and the ocean. Illicit connections can also work the other way – a storm drain can be connected to the sewer system. The problem in that case is greatly increased flows during rainfall events, leading to sewer overflows. In either case, the sewer and storm drain systems are intentionally or inadvertently connected, resulting in pollution.

An illicit discharge is defined as any discharge to the municipal separate storm sewer system that is not composed entirely of storm water, except for discharges allowed under a NPDES permit or waters used for firefighting operations. These non-stormwater discharges occur due to illegal connections to the storm drain system from homes, business or commercial establishments. As a result of these illicit connections, contaminated wastewater enters into storm drains or directly into local waters before receiving treatment from a wastewater treatment plant. Illicit connections may be intentional or may be unknown to the business owner or homeowner and often are due to the connection of floor drains to the storm sewer system. Additional sources of illicit discharges can be failing septic systems, illegal dumping practices, and the improper disposal of sewage from recreational practices such as boating or camping.

Illicit discharge detection and elimination (IDDE) programs are designed to prevent contamination of ground and surface water supplies by monitoring, inspection and removal of these illegal non-stormwater discharges. An essential element of these programs is an ordinance granting the authority to inspect properties suspected of releasing contaminated discharges into storm drain systems. Another important factor is the establishment of enforcement actions for those properties found to be in noncompliance or that refuse to allow access to their facilities.

Many cities and counties have IDDE programs. Typical procedures for detecting illegal connections to the Storm Sewer System are:

  • Survey individual buildings to discover where connections to storm drains exist.
  • Inspect sewer lines with television equipment to visually identify all physical connections.
  • Compare the results of the field tests and the video inspection with the known connections on piping plans or maps. Suspicious areas are then further investigated.
  • Institute mandatory inspections for new developments or remodeling to identify illicit connections to the storm sewer system.
  • Remove and test sediment from the catch basins or equivalent structures.
  • Inspect connections in question to determine whether they are connected to the storm drain system or to the sanitary sewer. Potential methods of identification include dye testing, visual inspection, smoke testing, or flow monitoring, as described below.
Washington Dept. of Ecology
  • Dye Testing. Flushing fluorometric dye into suspicious downspouts can be useful to identify illicit connections. Once the dye has been introduced into the storm system via the connection in question, the water in the collection system is monitored to determine whether an illicit connection is present.
  • Visual Inspection. Remotely guiding television cameras through sewer lines is another way to identify physical connections.
  • Smoke Testing. Smoke testing is another method used to discover illicit connections. Zinc chloride smoke is injected into the sewer line and emerges via vents on connected buildings or through cracks or leaks in the sewer line. Monitoring and recording where the smoke emerges, crews can identify all connections, legal and illegal, to the sewer system.

Smoke Testing (

  • Flow Monitoring. Monitoring increases in storm sewer flows during dry periods can also lead investigators to sources of infiltration due to improper connections.
  • Infrared, Aerial, and Thermal Photography. Researchers are experimenting with the use of aerial, infrared, and thermal photography to locate dischargers by studying the temperature of the stream water in areas where algae might be concentrated and in soils. It also examines land surface moisture and vegetative growth. This technique assumes that a failing on-site disposal system, for example, would have more moisture in the surface soil, the area would be warmer, and the vegetation would grow faster than in the surrounding area.

EPA has prepared a model ordinance which includes language to address illicit discharges in general, as well as illicit connections from industrial sites. The language is borrowed from a number of ordinances and communities will need to assess what enforcement methods are appropriate for their area. EPA has also prepared a Guidance Manual for Identifying and Eliminating Illicit Connections to Sewer Systems.

Surfrider Foundation, through its Blue Water Task Force program, has helped to uncover several instances of illicit connections, including at Larrabee State Park in Washington and in Newport and Cannon Beach, Oregon.


Illicit Discharges (U.S. EPA)

Guidance Manual for Identifying and Eliminating Illicit Connections (U.S. EPA)

Illicit Connection Amnesty Program (Town of Burlington, MA)

Illicit or Illegal Connections to the Storm Sewer System (City of Cumming, GA)


Illicit Discharge Detection and Elimination - A Guidance Manual (U.S. EPA, Center for Watershed Protection)

Stories about Getting to Clean Water: Stormwater Sleuths Solve the Mystery of the Putrid Pipe - Pullman’s hunt for the elusive, illicit discharge (Washington Department of Ecology)