Date of Award

6-2024

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Donald M. Reeves, Ph.D.

Second Advisor

Daniel P. Cassidy, Ph.D.

Third Advisor

David O. Zakharov, Ph.D.

Keywords

Adsorption, air-water interface, contaminant transport, per- and polyfluorinated alkyl substances, wastewater treatment

Access Setting

Masters Thesis-Open Access

Abstract

Fate and transport of per- and polyfluoroalkyl substances (PFAS) in wastewater treatment plant (WWTP) effluent discharged to rapid infiltration basins (RIBs) is investigated using data from 26 WWTPs in Michigan and numerical modeling to assess the role of air-water interface (AWI) sorption in modulating mass fluxes to the saturated zone. Analysis of RIB physical properties yields a median separation distance of 6.5 meters between land surface and the water table, and a continuum of area-normalized effluent fluxes ranging from 0.01 to 0.62 meters per day. A subset of WWTPs with RIBs indicate higher PFAS concentrations in groundwater than effluent with a median enrichment factor of 2.4 for the most frequently detected perfluoroalkyl acids. Enrichment factors of individual PFAS compounds as high as 13 are linked to a site with historical use of aqueous film-forming foams. Numerical modeling simulations show long-chain PFAS (e.g., PFOS, PFOA) undergo significant delays from AWI adsorption, requiring up to 14 times longer to reach maximum mass flux at the water table under low flux conditions where AWI area is 2.5 times greater. Short-chain PFAS commonly detected in effluent are only minimally affected by AWI adsorption. The nonlinear inverse relationship between water content and AWI area highlights the important role of AWI adsorption in modulating the unsaturated transport of long-chain PFAS to underlying groundwater due to the broad range of flux rates applied to RIB systems.

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