ASSESSING THE FATE AND TRANSPORT OF PFAS IN WASTEWATER TREATMENT PLANT EFFLUENT DISCHARGED TO RAPID INFILTRATION BASINS

Little is understood on the fate and transport of per- and polyfluoroalkyl substances (PFAS) released into the environment through rapid infiltration basins (RIBs). In this study, 26 wastewater treatment plants (WWTPs) with RIBs are identified within Michigan based on wastewater disposal methods designated on Michigan Part 22 groundwater discharge permits. Concentrations of PFAS in influent, effluent, and groundwater samples are analyzed from six of the WWTPs which currently have the PFAS data available. Enrichment factors of GW-effluent computed from these data vary for different PFAS and range from 1 to 17. Perfluorinated compounds, such as PFBA, PFBS, PFPeA, PFHxA, PFHpA, PFOA, and PFOS, demonstrate the greatest accumulation in groundwater with enrichment factors averaging 2.4. Exceedances of the maximum contaminant levels promulgated by the Michigan Department of Environment, Great Lakes, and Energy for drinking water occur for either PFOA or PFOS in shallow groundwater located within 100 meters of the RIBs at each of the sites. Physical site characteristics of all 26 plants are collected using the MiEnviro Portal or obtained directly from the WWTPs. Each site discharges treated municipal sewage that may have industrial wastewater contributions. Across the plants, RIBs are sand dominant and receive effluent flow rates between 200 and 18,000 m³/d with normalized fluxes of 0.03 to 0.62 m/d. Vertical separation distances between the surface elevation of the RIBs and groundwater elevation are 2-14 meters. Using the distribution of physical characteristics and PFAS concentrations compiled from Michigan WWTPs with RIBs, a series of HYDRUS-2D models are developed to simulate the fate and transport of PFAS in WWTP effluent to receiving groundwater. Comparisons of observations and simulated results are then used to identify the tendency of individual PFAS compounds to migrate and accumulate in shallow groundwater.