Managing and controlling stormwater and other "wet weather" discharges presents unique challenges, far different from the management and control of industrial and municipal wastewater streams. Wet weather discharges are periodic and unpredictable. They can contain varying concentrations and types of pollutants. The wet weather discharger can rarely know with any certainty when or how much water will need to be managed. The source of pollutants in these weather-related discharges is often difficult to discern, and sampling wet weather discharges is a challenge. In contrast, process and sanitary waste streams tend to be more consistent and predictable. The types and concentrations of pollutants generally remain the same, and when changes do occur, they are typically knowable in advance; the source of those pollutants is easily discernable; the timing and quantity of flows is foreseeable; and it is a relatively simple task to develop a sampling program. In light of these distinctions, it is appropriate that the requirements for managing, treating, and controlling wet weather discharges are different from those applicable to process and sanitary waste streams.