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Fate of poly and perfluoroalkyl substances in unsaturated AFFF-impacted vadose soil systems
Shea, Stefanie M.
Shea, Stefanie M.
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2024
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Abstract
Poly- and perfluoroalkyl substances (PFASs) are persistent and widespread environmental contaminants linked to adverse human health effects. Aqueous film-forming foam (AFFF)-impacted vadose soils serve as long-term sources for PFAS contamination to groundwater, even decades after release. PFASs in these soils can be influenced by solid-phase interactions as well as air-water interactions, including interfacial retention and volatilization. Understanding how these interactions affect the transport of PFASs is essential for evaluating the risk the contamination poses to receptors.
The first objective of this dissertation was to evaluate the influence of soil saturation on PFAS leaching from field-collected unsaturated AFFF-impacted soils using soil column experiments. Results of this work identified that air-water interfacial retention was more significant in the soil with lower organic carbon and variably saturated soil conditions increased PFAS mass flux from the soils when compared to constant saturation conditions. The second objective of this dissertation was to identify the effect of various soil properties on PFAS release and retention in unsaturated soils. Batch desorption and variably unsaturated column leaching experiments were used to assess the influence of solid-phase interactions as well as air-water interactions on PFAS leaching from each of the soils. The results showed that air-water interfacial retention was most substantial in the soil with low organic carbon content and high air-water interfacial area. The resultant data were used in linear regression analysis to identify the most important predictors for PFAS leaching from the variably unsaturated soils.
The final objective of this dissertation was to evaluate the extent of volatilization of PFASs from AFFF-impacted water. Gas phase concentrations of perfluoroalkane sulfonamides (FASAs) and perfluoroalkyl carboxylates (PFCAs) measured in the headspace above AFFF-impacted water indicated air-water partitioning for these components should be considered when assessing PFAS transport pathways from unsaturated soils and underscored the need for vapor intrusion modeling of these components.
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