Evaluation of Stormwater Treatment Vault with Coanda-Effect Screen for Removal of Solids and Phosphorus in Urban Runoff

Catch basins commonly are used by cities as part of a stormwater management plan to remove sediment and associated contaminants from stormwater, keeping them in compliance with regulations. Recently, the city of Madison, Wisconsin modified traditional catch basins by incorporating a fine-mesh (1-mm) Coanda-effect screen into the design with the goal of increasing removal of sediment and organic matter from stormwater. The US Geological Survey (USGS), in cooperation with the City of Madison, installed a water-quality monitoring station at such a catch basin to quantify reductions in total suspended solids (TSS), volatile suspended solids (VSS), suspended sediment concentration (SSC), total phosphorus (TP), and dissolved phosphorus (DP) from urban stormwater before entering Lake Monona. A comparison of the cumulative load from 33 samples collected during the summers of 2016 and 2017 showed 23% and 45% reductions in TSS and SSC, respectively. A smaller reduction was observed for TP, 16%, whereas DP remained unchanged. Reported traditional catch basin sediment removal varies greatly, although typical removal rates are similar. Results from this study will help regulated municipalities determine whether the use of screened catch basins can help meet water-quality goals.