Mark L Brusseau, PhD
Retention and Transport of PFAS in Source Zones
Investigations of sites contaminated by per- and poly-fluoroalkyl substances (PFAS) have demonstrated that the vadose zone can serve as a significant long-term source. In addition, nonaqueous-phase liquids (NAPL; chlorinated solvents, fuels) are present in source zones at some PFAS-contaminated sites. The presence of air-water and NAPL-water interfaces in these systems provides additional adsorption domains for PFAS retention, in addition to adsorption by the solid phase. It is critical to understand the retention and transport behavior of PFAS in these complex systems to improve the accuracy of risk assessments and the effectiveness of site characterization and remediation efforts. While previous research has established the significance of solid-phase adsorption, investigation of PFAS adsorption at air-water and NAPL-water interfaces has just begun. The aim of this research was to characterize and quantify the various processes that may occur in PFAS source zones in order to better understand PFAS transport behavior in complex systems. This research used PFOA and PFOS as model PFAS. Adsorption at the air-water interface in unsaturated systems was investigated with surface-tension measurements and miscible-displacement experiments with varying system conditions. Contributions to retention by NAPL were investigated with interfacial-tension measurements, miscible-displacement experiments, and NAPL-water partitioning experiments. Additionally, this research investigated the impacts of nonideal sorption/desorption and extended rate-limited elution behavior of PFAS. Laboratory experiments and various model simulations of PFAS sorption/desorption were employed to determine the appropriateness of different assumptions in accurately capturing sorption/desorption behavior of PFAS. Lastly, this research also investigated the influence of PFAS characteristics and solution composition on PFAS adsorption at fluid-fluid interfaces.