2023-11-292023-11-292022-12https://hdl.handle.net/2346/96944Per- and polyfluoroalkyl substances (PFAS) are persistent man made organic compounds used in a variety of products and applications such as aqueous film forming form (AFFF), food packaging, pesticides, and oil and water repellent coating. Application of AFFFs in fire training and emergency response sites is one of the primary sources of PFAS contamination to soil and groundwater. AFFF formulations include anionic, zwitterionic and cationic PFAS. Depending on the manufacturer and year of production, they may contain PFAS produced by either electrochemical fluorination (ECF) or fluorotelomerization. Whereas perfluoroalkyl substances such as perfluoroalkyl acids (PFAAs) do not degrade in the environment, polyfluoroalkyl substances (precursors) transform to terminal PFAAs by biotic and abiotic activity. Stronger sorption of cationic and zwitterionic polyfluoroalkyl substances in source zone soils, combined with slow biotransformation to PFAAs can represent a long-term source of PFAAs to the saturated zone. The objective of this work was to evaluate the potential for in-situ chemical oxidation (ISCO) and biosparging to enhance transformation of stronger-sorbing PFAS to more mobile, terminal PFAAs so that total PFAS can more readily be recovered during pump and treat remediation of AFFF impacted groundwater. Design, implementation, and monitoring of PFAS remediation approaches evaluated herein relies on the ability to evaluate the composition and concentration of total PFAS in soil and groundwater. This study utilized target analysis, total oxidizable precursors (TOP) assay, suspect screening coupled with semiquantitative (SQ) concentration estimates, and two soil extraction techniques to optimize estimation of total PFAS concentration in environmental media. Results showed applying the TOP assay followed by SQ analysis on post TOP samples may result in more representative of total PFAS concentration. However TOP is a bulk assay, so when project objectives include evaluation of the individual PFAS present, suspect screening with SQ analysis can be used to determine the individual PFAS present and estimate their concentrations. Extraction techniques were applied on 3 AFFF impacted soils, and results showed the comprehensive extraction approach led to 35% higher total PFAS concentration and improved extraction of cationic/zwitterionic suspect PFAS in one soil. However, the acidic solvent used in the comprehensive approach resulted in higher matrix effects which impacted estimation of PFAS concentrations using suspect screening with SQ analysis. So overall, it was determined that there was not an advantage to routine application of the comprehensive extraction method to all PFAS-impacted soils. Once sample preparation and analytical techniques were finalized, the present study applied chemical oxidation to treat AFFF impacted soils using batch and column experiments with the objective of evaluating precursor degradation and total PFAS mobilization using persulfate. Results of both batch and column experiments suggested that persulfate pre-treatment could be used as an effective flushing technique to enhance total PFAS recovery from impacted soils during groundwater extraction. Results of batch and column experiments were consistent, but column studies using two AFFF impacted soils were conducted to confirm batch experiment results under more field relevant conditions. Whereas nearly complete precursor transformation was seen in batch systems treated with heat activated persulfate, columns treated with the same approach showed partial precursor oxidation, suggesting that ISCO parameters such as oxidant dosage and number of oxidation pulses needs to be optimized for each site. Batch and 1-D column test were also used to evaluate the effect of oxygen infusion on precursor biotransformation of precursors to PFAAs and any resulting changes to PFAS mass transport in groundwater. Batch tests were conducted on an AFFF impacted soil, and oxygen was sparged directly into a soil water slurry. Results showed faster degradation of precursors in oxygen sparged reactors resulted in faster desorption of PFAS in aqueous phase in relative to control reactors. In order to evaluate change in PFAS mass transport during in-situ biosparging, columns packed with two AFFF impacted soils were injected with oxygen sparged artificial groundwater (AGW). Due to the gas permeability of the column tubing, DO concentrations in column influent were lower than in the directly sparged batch reactors, however, DO in air sparged columns was still higher than ambient control columns. Analysis of effluents showed no change in total PFAS recovery due to biosparging. However, analysis of PFAS remaining column soils after experiments were completed showed that less PFAS mass was retained in oxygen sparged columns and suggesting that higher oxygen concentration might result in more biotic or abiotic precursor transformation. Findings of this study set the stage to scale this techniques up to pilot and eventually field scale approaches that can be used to improve the efficiency of remediation of PFAS-impacted groundwater. Specifically, current treatment techniques that are capable of PFAS destruction rely on extraction of groundwater and ex situ treatment, so techniques investigated herein may be beneficial to improve the efficiency of the PFAS extraction process. Specifically, it may reduce the duration of pumping required for effective total PFAS extraction, thus lowering the time, energy, and cost associated with pumping and remediation system maintenance. Although results suggested that ISCO had was more effective in transforming and mobilizing PFAS, this technique may not be appropriate at all field sites due to factors such as the potential for altering subsurface geochemistry. In such situations, biosparging may still be considered, although this method needs further evaluation to establish potential as a flushing approach. Results herein also have important implications for legacy sites where these approaches have been applied to remediate co-occurring contaminants such as chlorinated solvents and hydrocarbons. At these sites, it is possible that unintentional precursor transformation and PFAA mobilization occurred, which highlights the importance of understanding detailed site history when evaluating and prioritizing PFAS-impacted sites.Embargo status: Restricted until 01/2024. To request the author grant access, click on the PDF link to the left.Application/pdfenPer- and polyfluoroalkyl substancesaqueous film forming formTotal oxidizable precursorsNon-targeted analysisSorptionIn-situ remediationPersulfate chemical oxidationBiospargingDissertationRestricted until 01/2024.