Assessing the performance of sand filter basins in treating urban stormwater runoff

This study has assessed the efficiency of sand filter basins in treating urban stormwater runoff by analyzing available data in the literature, the International Stormwater BMP Database, and data collected in a sand filter basin located in the main campus of the University of Texas at San Antonio (UTSA). Ten storm events were monitored starting in March 2016 until February 2017. Total suspended solids, volatile suspended solids, nitrate, ortho-phosphate, copper, zinc, lead, pH, and conductivity were measured in the inlet and the outlet of the basin. Statistical analysis, including linear regression modeling, scatter plotting, and non-parametric testing, using data from the literature and the International Stormwater BMP Database was performed. The sand filter basin removed, on average, 94% and 86% of TSS and VSS, respectively. Such high removal rates were not observed for other constituents, with exception of lead (79%) that already showed a low mean concentration in the inlet of the basin (41.47 ± 27.41 μg/L). Nitrate and ortho-phosphate mean concentrations were not significantly different in the outlet than inlet. The basin effluent concentration of zinc was higher than acceptable stormwater benchmarks defined by EPA. The results indicated that the monitored sand filter basin met its primarily design criteria, which is TSS removal by at least 80% of mass. Better stormwater treatment practices, however, are needed to remove other pollutants more efficiently, in particular, because this area is located on top of the recharge zone of the Edwards Aquifer, a major source of water supply for the region.