As per- and polyfluoroalkyl substances (PFAS) are both highly recalcitrant and mobile, groundwater plumes continue to expand both within and beyond facility boundaries, potentially further increasing the number of impacted wells and the overall treatment costs. While ex situ treatment approaches are progressing, and full-scale systems are currently operational, validated in situ approaches to treat PFAS in groundwater are lacking. The primary objective of this project is to demonstrate the ability of a powdered surface modified clay (SMC) to be distributed via direct-push technology (DPT) injection to sequester and reduce mass flux of PFAS-impacted groundwater.

Injected Surface Modified Clay PAB for PFAS Treatment

While there are currently no proven in situ technologies to destroy PFAS in groundwater aquifers, in situ amendments designed to sorb PFAS (e.g., powdered and colloidal activated carbon [CAC], modified and organo-clays, mixed-mineral adsorbents, powdered and colloidal anion exchange resins, biochar) have been evaluated in laboratory studies, and some (particularly CAC) are being applied and evaluated in the field (e.g., ESTCP Project ER20-5182). While in situ sequestration of PFAS via the injection of a powdered SMC is a promising treatment approach, the technology has not received the necessary independent scientific scrutiny to determine the following factors.

• loading and distribution in aquifers;
• general effectiveness on different molecular structures comprising PFAS;
• long-term adsorption capacity of the permeable adsorptive barrier (PAB); and
• potential detrimental effects, such as the reduction of aquifer permeability within the treatment zone and transport into local monitoring wells.

During the field demonstration, a pilot-scale in situ PAB barrier will be installed to sequester and reduce mass flux of PFAS within an impacted aquifer. A slurry containing powdered SMC will be emplaced using a DPT drill rig and special injection equipment and tooling that provide high energy injections which fluidize the formation to allow radial distribution of the particulate amendments from each of the injection points (spaced ~5 ft apart). In sandy aquifers, a high-emplacement velocity is used to overcome the natural filtering effects of the lithology and create radial mixing within the treatment zone. Unlike injecting CAC, which involves relatively low concentrations (~2 to 3 %) of CAC in high volumes of solution injected at low pressures and flow rates, the high energy slurry injections involve high concentration slurries (typically 5 to 50%) at appreciably lower injection volumes and higher injection pressures and flow rates. Therefore, this injection method can deliver a higher mass of particulate amendments quickly, with less chance of daylighting and/or displacement of chemicals.

This project will facilitate an independent, objective evaluation of the effectiveness of an in situ method for the long-term mitigation of PFAS-impacted groundwater that could be readily implementable at many locations. There are many different PAB configurations possible for this technology, making it applicable at a variety of sites. The analysis conducted during this project will provide an independent evaluation of this technology and is expected to show both the long-term potential of the technology as well its possible limitations. Successful completion of this effort will ultimately improve the cost-effectiveness of PFAS treatment technologies, directly benefiting the warfighter and installation communities. (Anticipated Project Completion - 2028)