Which of the following is an example of a non-stormwater discharge that is often exempt from illicit discharge prohibitions?

• A. Landscape irrigation runoff (when not contaminated)
• B. Stormwater runoff from rainfall
• C. Firefighting flows
• D. Industrial process wastewater

Answer: (C)

Non-stormwater discharges can be exempt when they’re necessary for safety or essential operations and aren’t pollutants that undermine the stormwater program. Firefighting flows fall into this category because they’re part of emergency response to protect lives and property; the priority is a rapid, effective fire response, so these discharges are allowed to enter the drainage system even though they’re not stormwater. While other non-stormwater discharges might be exempt in some contexts (for example, landscape irrigation runoff that isn’t contaminated can be considered permissible in some programs), firefighting flows are a clearly recognized exception due to their urgent public safety purpose. In contrast, discharges from rainfall are not non-stormwater at all, and industrial process wastewater typically requires permitting or specific authorization.