Stormwater Treatment Systems

Certain stormwater treatment devices reduce pollutant loads by effecting a reduction in contaminant concentration, without modifying the flows that they process (e.g., filters and screens). Performance ratings for such devices are normally defined in terms of a removal efficiency at a specific flow or hydraulic loading rate. Actual performance, however, will vary from storm to storm, depending on the inherent variations in storm runoff characteristics. A statistical method of analysis is described that estimates the long-term performance efficiency of treatment devices subjected to the varying rainfall-runoff process. Treatment processes with removal efficiencies sensitive to flow and influent concentration are analyzed. Issues addressed include the effect of flow bypass, flow and concentration variation between and within storms, and the implications of flow-concentration correlations in the storm runoff or combined sewer overflow. Treatment performances predicted by the statistical method are compared with results predicted by simulation modeling techniques.