Illicit Discharge Detection & Elimination

An illicit discharge is defined as any release into the drainage system of contaminated water or any non-stormwater discharge that contributes pollutants to receiving waters.

Increased and contaminated stormwater runoff is a major cause of: 

  • impairment of water quality and flow in lakes, ponds, streams, rivers, wetlands and groundwater; 
  • contamination of drinking water supplies; 
  • alteration or destruction of aquatic and wildlife habitat; and 
  • flooding. 

Examples of Illicit Discharges

  • Sanitary wastewater from crushed or collapsed pipes or surcharges
  • Direct septic connections into the storm drain system
  • Overflow from septic tanks, car wash wastewater
  • Laundry wastewater
  • Improper disposal of automobile and household products
  • Bagged or unbagged dog waste
  • Leaves and other debris dumped into open drainage and stream channels

Discharge Exceptions

Exceptions (not considered illicit discharges):

  • Water line flushing
  • Landscape irrigation
  • Diverted stream flows
  • Rising or out-breaking groundwater
  • Uncontaminated pumped groundwater (includes clean sump pump discharges)
  • Potable water source discharges
  • Foundation drains
  • Dechlorinated swimming pool discharges
  • Stormwater runoff from streets and sidewalks

IDDE Plan for the MS4 Program

Weston’s Illicit Discharge Detection and Elimination (IDDE) Plan has been developed to address the requirements of the Environmental Protection Agency’s 2016 National Pollutant Discharge Elimination System (NPDES) General Permit for the Massachusetts MS4 Permit. 

The IDDE program is implemented to systematically find and eliminate sources of non‐stormwater discharges to its municipal separate storm sewer system and implement procedures to prevent such discharges. 


Regulation of illicit connections and discharges to the Town of Weston municipal storm drain system is necessary for the protection of the town’s water bodies and groundwater and to safeguard the public health, safety, welfare and the environment. 

The regulation is covered by Article XXXI - Illicit Discharge By-law (PDF) with the purpose to:

  • prevent pollutants from entering Weston’s municipal separate storm sewer system (MS4);
  • prohibit illicit connections and unauthorized discharges to the MS4;
  • require the removal of all such illicit connections;
  • comply with state and federal statutes and regulations relating to stormwater discharges; and
  • establish the legal authority to ensure compliance with the provisions of this By-law through inspection, monitoring, and enforcement.

By-law Enforcement

The Department of Public Works conducts inspections of stormwater outfalls throughout Weston as part of ongoing compliance with our Phase II permit. Article XXXI - Illicit Discharge By-law (PDF) provides enforcement and fining procedures for illicit discharges found within the Town’s MS4. Any discharge deemed a threat to public safety, public health, or the environment is in violation of this by-law and thus subject to a removal order and / or fines by the Department of Public Works, Conservation Commission, Board of Health, or Inspectional Services. 

Additional Information

For more information on illicit discharges, view the New England Interstate Water Pollution Control Commission’s Illicit Discharge Detection and Elimination Manual (PDF)

For more information regarding the Phase II Stormwater Management Program, contact Richard Sweeney, Assistant Town Engineer/Stormwater Engineer at 781-786-5117.