Stormwater BMPs and Trace Organic Contaminants

Urban stormwater can be an important pathway for trace organic contaminants (TrOCs) to enter the environment. Best management practices (BMPs) are often used to mitigate the hydrologic and chemical effects of urban stormwater on receiving waters. Previous research mostly focused on BMP ability to reduce nutrients and metals, but recent work suggests that BMPs may also reduce TrOCs in stormwater.

From 2018 to 2020, we conducted two studies on the fate of 217 pesticide and 110 pharmaceutical TrOCs in stormwater: (1) removal by iron-enhanced sand filter (IESF) ponds, and (2) transport to shallow groundwater from underground infiltration basins (UIBs). A total of 4 IESF ponds, 2 traditional ponds, and 2 UIBs were sampled throughout the Twin Cities Metropolitan Area. Samples were collected from the inflows and outflows from sand filters at IESF ponds, inflows and outflows at traditional ponds, and inflows and shallow groundwater at UIBs. Pressure transducers were installed in monitoring wells adjacent to UIBs for one year to monitor groundwater hydrology.

Preliminary data show that 15 pesticides and 6 pharmaceuticals were detected in 30% of all samples collected from IESF and traditional ponds fewer were detected in samples collected from UIBs than in ponds. More pesticides were detected and at higher concentrations in some IESF and traditional pond outflows, compared to inflows. Pharmaceuticals were slightly lower in outflow compared to inflow. Generally, fewer TrOCs were detected in groundwater compared to inflow at UIB, and at lower concentrations. Groundwater hydrographs show that the two UIBs have differing measured effects on the local groundwater table. An almost immediate recharge is evident at one site, while the other shows no apparent direct relation with infiltration.

Results show that stormwater BMPs may provide an added benefit by removing some TrOCs from the environment, but questions remain regarding the fate of TrOCs within BMPs.