Evaluation of oil and grease from roadway runoff in sediment from detention basins and swales within the Edwards Aquifer recharge zone, central Texas, U.S.A.

In this study, we evaluated the oil and grease concentrations in sediment from roadway runoff in detention basins and swales following rain events. The study was conducted in three swales and two detention basins within the Edwards Aquifer recharge zone in San Antonio, Texas and one swale located in the contributing zone. The Edwards Aquifer is the primary source of municipal water for Bexar and surrounding counties and being a karst aquifer makes it susceptible to pollution. Oil and grease was sampled following eight rain events in detention basin (n = 3) and swales (n = 3) from November 2020 to July 2021 using pitfall traps. Mean oil and grease concentrations in detention basins and swales were 723 mg kg⁻¹ (SE = 41.6) and 667 mg kg⁻¹ (SE = 41.9), respectively, indicating these stormwater management structures are efficient at capturing oil and grease from roadway runoff. Mean sediment weight captured in pitfall traps was 2.6-fold greater in confined detention basins (6475 g m^2-1; SE = 1193) compared to swales (2443 g m^2-1; SE = 526). Nonmetric Multidimensional Scaling (NMS) indicated that particle sizes of 125, 250, and 500 μm were moderately associated with oil and grease concentrations on axis 1. Detention basins and swales should be promoted for future development in the Edwards Aquifer contributing and recharge zones for management of oil and grease and other pollutants associated with roadway runoff and other impervious structures for protection of groundwater and the associated listed species.