Illicit Discharge
What is an illicit discharge?
An illicit discharge is defined as any discharge to the municipal separate storm sewer system (MS4) that is not composed entirely of stormwater, except for discharges allowed under a TPDES permit. Non-stormwater discharges can originate from direct connections to the storm drain system from business or commercial establishments (illicit connections), or indirectly as improper surface discharges to the storm drain system.
What types of discharges to the storm drain system are prohibited?
The following table lists some of the prohibited and allowed discharges to the storm drain system.
| Prohibited Discharges | Allowed Discharges |
| Industrial process water | Water utility line flushing |
| Commercial car wash wastewater | Runoff from firefighting |
| Sanitary sewer flows | Landscape irrigation |
| Wash-down of loading areas | Uncontaminated ground water infiltration |
| Wastewater treatment plant effluent | Discharges from potable water sources |
| Dumping of liquid waste | Dechlorinated pool water |
| Chlorinated pool water | Street wash water from cleaning/maintenance (excluding street sweeper water waste) |
| Water softener brine backwash | Residential car washing |
| Used oil | Air conditioning condensation |
What are indications of illegal/illicit discharges to the storm drain system?
The following table lists some of the physical indicators that may signal an illicit discharge; physical indicators are those that can be observed or sensed during dry weather field screening and routine inspections.
| Unusual color or cloudiness |
| Strong pungent or musty odor |
| Floating debris |
| Surface scum or foam |
| Oil sheen |
| Algae |
| Dead vegetation or inhibited growth |
| Dead animals |
| Stains on channel bottom or sides |
| Pipe corrosion |
Workshops
- Illicit Discharge Detection and Elimination Training DVD
- IDDE companion poster for training DVD
- With black bordered photos PDF
- With red bordered photos PDF
- With yellow bordered photos PDF
- All three versions in InDesign zipped
- Municipal Employee Training Resources for Recognizing and Reporting Illicit Discharges:
- Illicit Discharge Detection and Elimination Field Investigation Guide
- Floatables Management Study and Control Technologies
- Dry Weather Field Screening Regional Protocol
- Dry Weather Field Screening Sample Reports
- Model Stormwater Ordinance – Provisions for Small MS4s to Control Illicit Discharges
- Potable Water Fish Kills Factsheet
- Automotive Related Business Flyer and Pamphlet
- Publisher zipped files in Spanish and English
- Manure Management BMP Brochure
- Construction General Permit 2023 Infographic
EPA
- NPDES Illicit Discharge Detection and Elimination: Information, Key Best Management Practices, and Resources
- Model Ordinances for Illicit Discharges
- NPDES Recorded Webinars and Training
- Climate and Extreme Weather Tools for the NPDES Program
TCEQ
Other Resources
- Center for Watershed Protection: Illicit Discharge Detection and Elimination: A Guidance Manual for Program Development and Technical Assessments
- Wayne County, Michigan: Illicit Discharge Elimination Training
- Caltrans: Statewide Stormwater Program
- City of Fort Worth: Stormwater Ordinance
- New England Interstate Water Pollution Control Commission: Illicit Discharge Detection and Elimination Manual