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Transport of perfluorinated substances in vadose zone: aqueous film-forming foams source zone, release from the source and transport
Vahedian, Faran
Vahedian, Faran
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2024
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2026-04-04
Abstract
Per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals”, have garnered significant attention due to their widespread use, persistence, bioaccumulation potential, mobility, and toxicity to humans and animals. These characteristics have prompted extensive global public and regulatory scrutiny. PFAS concentrations reach alarming levels of up to mg/L in groundwater, while recent regulations aim to limit two common PFAS compounds to just 4 ng/L. PFAS have been detected at historic aqueous film-forming foams (AFFF)-impacted sites, concentrated in shallow soil layers, forming a critical reservoir source zone for long-term groundwater contamination. Understanding complex transport processes within the vadose zone such as tension-driven flow, solid-phase interactions, air-water interfacial interactions, and unsaturated soil physics, is crucial for assessing contamination risks and developing effective remediation strategies.
This thesis research investigated transport of PFAS originating from and moving through the vadose zone. It explores the characteristics of an AFFF source zone, the release of PFAS from these zones, and their migration within the unsaturated zone toward the groundwater table, where PFAS can impact human receptors. The first research objective evaluated the influence of tension-driven flow on the lateral spreading of AFFF in the vadose zone and the growing size and footprint of the AFFF source zone. The second objective centered on PFAS transport mechanisms in or near AFFF source zones, focusing on solid-phase sorption and how PFAS sorption dynamics, both equilibrium and kinetics, differ between AFFF-impacted and pristine media. The final objective explored how PFAS transport in the vadose zone varies across transient infiltration regimes and moisture content levels, hypothesizing that kinetic partitioning would be more important during transient unsaturated flow and transport. To address all the objectives, laboratory-scale experiments incorporating the selected mechanisms were conducted and numerical investigations were employed to enhance our understanding of PFAS transport and partitioning in vadose zone environments.
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