Water quality performance assessment of two stormwater detention basins located in the recharge zone of a karst aquifer.

Stormwater detention basins are used to minimize peak discharges and improve water quality mainly through sedimentation; however, limited studies have evaluated the water quality performance of detention basins located over karst aquifers. Karst aquifers are vital sources of drinking water for many regions of the world and their recharge areas are susceptible to contamination from surface water resources. In this study, an analysis of two stormwater detention basins (namely, Kyle and TPC) located in the recharge zone of one of the most prolific karst aquifers in the world (Edwards Aquifer, San Antonio, Texas), were conducted over a period of one year to quantify the water quality and hydrologic performance of the basins. Automated samples were collected during the storm events and analyzed for nitrate (NO-N), nitrite (NO-N), ammonia (NH-N), total dissolved nitrogen (TDN), phosphorus (PO), total suspended solids (TSS), total dissolved solids (TDS), total carbon (TC), total organic carbon (TOC), and chemical oxygen demand (COD). Both basins reduced NH-N, TSS and COD concentrations significantly while NO-N and PO concentrations exhibited a net export. Furthermore, TPC showed greater reductions in NO-N, TOC and TC concentrations compared to Kyle. Higher TSS removal was observed at TPC due to differences in retention time. A volume reduction of 44% and 64% was observed in TPC and Kyle, respectively. The results of this study demonstrate that stormwater detention basins located over the Edwards Aquifer effectively remove particulate pollutants while also being a potential source of dissolved pollutants such as nitrate. Overall, the results presented here have important implications for operation and maintenance of stormwater basins constructed over recharge zones of Edwards Aquifer.