Extraction, transport, and transformation of poly- and perfluoroalkyl substances in soils impacted by aqueous film-forming foam

Abstract

Poly- and perfluorinated alkyl substances (PFASs) are a class of recalcitrant environmental contaminants used in a variety of industries and consumer products. Use of aqueous film-forming foams (AFFF) at military bases and airports is one significant source of PFAS contamination to groundwater and communities. AFFF formulations are composed of diverse PFAS classes, including anionic, zwitterionic, and cationic structures. Many of the polyfluorinated substances have been shown to transform to the perfluorinated substances in the environment. Despite years of research concerning the mostly perfluorinated anionic substances, the fate and transport of the zwitterionic and cationic PFASs remain largely unknown.The objective of this dissertation was to develop a better understanding of the transport and transformation of PFASs at AFFF-impacted sites, with a particular focus on zwitterionic and cationic compounds. The first research objective was to develop a soil extraction method to enhance the recovery of all PFASs. The second research objective was to conduct a comprehensive site characterization via high spatial resolution sampling of soil and groundwater samples with estimated concentrations of all detected PFASs. The final research objective was to simulate biosparging of an AFFF-impacted soil in column experiments to understand changes in PFAS transformation and release from source zone materials altered by remediation. The results indicated that a combination of strongly basic followed by strongly acidic extraction conditions were needed to achieve sufficient recovery of all PFASs from soils. The site characterization showed that the majority of the polyfluorinated mass remained near the source zone despite decades since release, and the majority of these compounds were zwitterionic or cationic. The third research effort showed that biotransformation of polyfluorinated precursors occurred in both O2-sparged and N2-sparged soil columns, and higher concentrations of certain zwitterionic PFASs eluted from O2-sparged columns shortly after start of sparging. The findings from this dissertation will allow for a more comprehensive view of the PFASs in the subsurface and how they move and change with time. These efforts will benefit remedial plans and site investigations at AFFF-impacted sites.