What is defined as an "illicit discharge" in stormwater management?

An "illicit discharge" in stormwater management is understood as a discharge to a storm sewer system that is not composed entirely of stormwater. This definition emphasizes that any substance entering the stormwater system, aside from natural rainwater or melted snow, can be considered illicit. Such discharges often include pollutants from industrial runoff, improperly managed wastewater, or other contaminants that negatively impact water quality. This concept is crucial because stormwater systems are typically designed to manage only rainwater, and the introduction of non-stormwater pollutants can lead to significant environmental harm, including water pollution and harm to aquatic ecosystems.

The other options do not capture the essence of what constitutes an illicit discharge in this context. For example, water from construction activities may often be regulated and managed to minimize its impact, while runoff from agricultural practices is generally considered as part of agricultural stormwater management rather than an illicit discharge. Similarly, controlled discharges from wastewater treatment plants are typically permitted and managed under specific regulations, meaning they are not categorized as illicit discharges either.