This proof-of-concept project will develop the fundamental knowledge needed to implement a new in situ treatment approach termed the In Situ Engineered Mineral Sorption (ISEMS) for capturing per- and polyfluoroalkyl substances (PFAS) in groundwater through enhanced sorption to an engineered in situ reactive mineral zone. In short, soluble metals are injected into an aquifer and then subsequently precipitated. The high concentrations of engineered metal oxide/oxyhydroxide/hydroxide minerals will sorb PFAS and function as a permeable reactive zone. This zone could be periodically “recharged”. Furthermore, unlike current colloidal-activated carbon-based alternatives, the engineered minerals can be intentionally dissolved (through pH and/or oxidation-reduction [redox] manipulation), allowing the release and immediate recovery (via pumping) of previously sequestered PFAS.

Several laboratory-based tasks will be conducted to characterize PFAS sorption to synthetic iron and aluminum minerals prepared in the laboratory, and PFAS release through manipulation of geochemical variables, such as pH, redox potential, or ionic strength. Overall, the focus of this work will be on two key hypotheses.

• Hypothesis 1: Iron and aluminum metal oxide minerals sorb PFAS through electrostatic, hydrophobic, and ligand exchange mechanisms, with specific metal oxides having a greater capacity for sorption.
• Hypothesis 2: PFAS desorption from metal oxides can be controlled by perturbing the pH, redox conditions, or ionic strength of the aqueous environment.

Following these experiments, tank tests will be conducted to develop practical methods for the implementation of the ISEMS approach. If successful, a limited field pilot test will be completed.

The information obtained through these studies will elucidate key driving processes and inform how best to deploy the technology in follow-on field demonstrations. Ultimately, it is hoped ISEMS can achieve PFAS mass flux reductions exceeding 99% and allow subsequent recovery of sequestered PFAS for ultimate destruction. As such, this would be a distinct advance over current in situ approaches for PFAS. Furthermore, it is expected the reactive mineral zones could be readily refreshed as needed, and therefore provide a viable long-term solution for PFAS treatment mass discharge control. More broadly, this work will support the development of in situ treatment strategies for PFAS. This work will also contribute to the understanding of PFAS interactions with metal minerals in aquifer systems. The successful execution of this research will yield data essential for the development of advanced technologies aimed at enhancing ongoing remediation efforts at PFAS-impacted sites, thereby providing crucial safeguards for warfighters and installation communities. (Anticipated Project Completion - 2026)