Illicit Discharge Detection & Elimination

The Illicit Discharge and Elimination (IDDE) program is an essential component of the Municipal Separate Storm Sewer System (MS4) permit requirements and refers to the unauthorized or illegal release of pollutants into stormwater drainage systems, which can ultimately lead to water pollution in streams, rivers, and other bodies of water. Illicit discharges can come from various sources such as industrial processes, improper disposal of household chemicals, and even accidental spills. The goal of Illicit Discharge and Elimination programs is to identify and eliminate these unauthorized discharges through monitoring, inspections, and public education. This helps to protect water quality, safeguard the environment, and ensure that stormwater systems function as intended.

Illicit Discharge


  • Chemical Dumping: Unauthorized disposal of chemicals, oils, paints, solvents, or hazardous substances into storm drains or drainage systems.
  • Sewage or Wastewater: Intentional or accidental discharge of untreated sewage, industrial wastewater, or sanitary waste into stormwater systems.
  • Vehicle Fluids: Leakage or dumping of motor oil, antifreeze, brake fluid, or other automotive fluids into storm drains.
  • Pet Waste: Excessive pet waste washed into stormwater systems, which can carry harmful bacteria and pollutants.
  • Litter and Trash: Discarding litter, debris, plastics, or other waste materials into storm drains that can lead to water pollution.
  • Construction Runoff: Sediments, construction materials, and debris from construction sites entering stormwater systems due to poor erosion control measures.
  • Agricultural Runoff: Excessive fertilizer, pesticides, and animal waste washing into stormwater systems from agricultural activities.
  • Illegal Connections: Direct septic connections that discharge into stormwater systems.
  • Washing Equipment: Discharge of car washing detergents or other cleaning chemicals into storm drains.
  • Industrial Processes: Discharging pollutants from industrial processes, such as heavy metals, chemicals, or toxins, into stormwater systems without proper treatment.
  • Improper Landscaping Practices: Overuse of fertilizers, herbicides, and pesticides that can be washed into storm drains during rainfall.
  • Septic System Failures: Malfunctioning or poorly maintained septic systems that release untreated sewage into stormwater systems.

Illicit discharges like these can have detrimental effects on water quality, aquatic ecosystems, and public health. The Town of Concord's IDDE program is crucial to identifying and preventing such discharges to ensure the protection of our environment and water resources.


  • Rainwater from rooftops
  • Stormwater from paved surfaces (roads, sidewalks, driveways)
  • Irrigation water from lawns and landscapes
  • Dechlorinated swimming pool water
  • Diverted stream flows
  • Springs and groundwater sources
  • Foundation drains
  • Water from air conditioning condensation
  • Potable water sources such as water main flushing

It's important to note that these discharges are typically considered acceptable because they do not contain pollutants that could harm the environment or water quality. However, an acceptable discharge becomes illicit when it includes pollutants or contaminants, such as chemicals, sewage, or waste, that can potentially harm the environment and water quality.


CPW will be conducting inspections of stormwater outfalls throughout town as part of our ongoing compliance to our Phase II Stormwater Management Plan. If pollutants or irregular flows are detected, the system will be traced back to find the source of the illicit discharge. Please note that regulations are currently being proposed within the town to develop an enforcement and fining procedure for illicit discharges found within the Town's MS4. Any discharge deemed a threat to public safety or public health is automatically in violation of the health code and is thus subject to a removal order and/or fines by the Health Department. For more information on illicit discharges, view the New England Interstate IDDE Manual website.

For Additional Information

For more information regarding the Phase II Stormwater Management Program, contact Concord Public Works at 978-318-3210.