The use of aqueous film-forming foams has created sites where soil and groundwater are highly impacted by per-and polyfluoroalkyl substances (PFAS) and other related chemicals. The presence of PFAS at many of these sites poses a direct threat to groundwater and surface water resources. As such, there is an urgent need for technologies that can contain PFAS to mitigate their risks. The overarching objective of this research is to improve the understanding of the capability of commercially-available activated carbon (AC) (including powdered activated carbon [PAC] and colloidal activated carbon [CAC]) to immobilize PFAS in situ. This project will investigate factors affecting the adsorption and desorption of PFAS on AC in the presence of co-occurring chemicals, the transport and attachment of CAC in porous media, and the long-term adsorption capacity and potential for PFAS re-release.

This research project will evaluate the in situ immobilization of groundwater plumes containing PFAS by AC barriers that are created by injecting PAC or CAC into the subsurface. The research will involve bench-scale experiments to elucidate the fundamental processes that govern the adsorption/desorption of PFAS, and the development of a novel reactive transport model capable of predicting the retention and breakthrough of PFAS in AC barriers. A field-scale experiment will be conducted to assess the retention of PFAS under more complex hydrogeochemical conditions and to benchmark the performance of the reactive transport model. The specific tasks of this research project are as follows:

1. Determine the effects of geochemical conditions and competitive sorption among PFAS and co-occurring chemicals on the adsorption and desorption of PFAS to PAC and CAC;
2. Elucidate the mechanisms that govern the transport and binding of CAC in porous media, and the adsorption/desorption of PFAS in a CAC or PAC barrier;
3. Develop a reactive transport model capable of predicting the transport of CAC, and the behavior of PFAS in a PAC or CAC barrier; and
4. Conduct a controlled field trial to evaluate the ability of a CAC or PAC barrier to immobilize a PFAS plume.

The research outcomes will enable informed prediction of the long-term effectiveness of the in situ immobilization of PFAS by particulate AC amendments. As sites impacted by PFAS are widespread in the U.S. and around the world, this research will not only provide great benefits to the Department of Defense (DoD), but also will generate knowledge that will be of significant interest to the broader scientific and engineering community as well as regulators responsible for remediation, reclamation, and management of impacted sites. The reactive transport model that will be developed in this project will be of value for risk assessment and remediation of sites impacted by PFAS. While this project focuses specifically on PFAS, the knowledge generated is expected to be relevant to the remediation of other chemicals of concern to DoD sites such as chlorinated volatile organic compounds and petroleum hydrocarbons. Additionally, an improved understanding of the factors affecting the distribution of CAC in porous media is expected to provide a foundation for improving the distribution of CAC and other particulate amendments in the subsurface. (Anticipated project completion - 2024)