Define illicit discharge in the context of stormwater management.

• A. A discharge that includes non-stormwater and is not exempt.
• B. Discharge that is allowed by permit.
• C. Any discharge to a storm sewer system that is not comprised solely of stormwater, and is not exempt or allowed by permit.
• D. Discharge that occurs only during rainfall.

Answer: (C)

Illicit discharge means any discharge to the storm sewer system that is not comprised solely of stormwater and is not exempt or authorized by a permit. This definition matters because the storm drain network is intended to carry only rainwater runoff; when non-stormwater (or pollutants) enter that system, it can carry pollutants to streams, lakes, or other waters. The element about being “to a storm sewer system” is essential, as is the distinction that the discharge isn’t exempt and isn’t allowed by a permit. If a discharge is permitted by a valid permit, or if it’s an exempt flow, it is not considered illicit. Also, illicit discharges can occur during dry weather, not just during rain, so a discharge that happens only when it’s raining isn’t automatically illicit.