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, or indirectly as improper surface discharges to the storm drain system. The result of these direct and indirect illicit discharges is that wastewater that should receive treatment from a wastewater treatment plant directly enters storm drains and local surface waters.

Illicit plumbing connections may be intentional or may be unknown to the business owner 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.

• Types of prohibited and allowable discharges to the storm drain system
• Indications of illegal/illicit discharges to the storm drain system
• Stormwater illicit discharge resources

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