The overall goal of this project is to assess the long-term adsorptive capacity of injectable particulate amendments used for in situ treatment of per- and polyfluoroalkyl substances (PFAS) in mixed plumes. Specifically, this project will investigate the impacts of biogeochemical conditions, PFAS composition and concentration, and the presence of hydrocarbon co-occurring chemicals on both adsorption and desorption for two commercially available amendments. The fundamental questions being investigated include:

1. How do PFAS concentration and composition (including anionic, cationic, and zwitterionic PFAS species) affect long-term adsorption capacity?
2. How do co-occurring chemicals affect PFAS treatment?
3. How do biogeochemical conditions, including the potential for precursor transformation and biofilm formation, impact long-term performance?
4. Can a predictive model of treatment performance be developed to aid in screening-level decision making processes?

This project will address knowledge gaps regarding particulate amendment treatment including: 1) treatment longevity, 2) wide range of PFAS in groundwater, 3) effect of co-occurring chemicals, 4) groundwater conditions, and 5) back diffusion and rebound of adsorbed chemicals over time. To achieve the project objectives, a carefully designed set of batch studies, column studies, and modeling will be conducted to provide a fundamental understanding of sorption behavior of PFAS onto the particulate amendments. Specifically, the focus will be on developing a key set of short-term testing that can be performed using the injectable amendments that, when coupled with the models developed herein, will serve as a tool for estimating long-term in situ treatment performance.

Batch experiments, using both natural and synthetic ground waters, will focus on multicomponent sorption effects, geochemical impacts, and desorption processes to build a robust knowledge on equilibrium time, sorption capacity and isotherm nonlinearity for these amendments under realistic geochemical conditions. Columns studies will evaluate the long-term adsorptive and desorptive behavior of the particulate amendments under simulated aquifer conditions. A key component of the column studies will be, in conjunction with the modeling, to determine the extent to which long-term treatment can be predicted from relatively short-term batch or column testing. Finally, multicomponent sorption models will be developed that are applicable to various geochemical conditions, PFAS concentrations and compositions, and biotic effects to predict long-term behavior of particulate amendments. Data from batch and column tests will be used to parametrize a one-dimensional advection-dispersion transport model that considers non-ideal sorption and transport effects, and its suitability for informing screening-level decision-making processes regarding site-specific selection of particulate amendments to prevent desorptive release of PFAS will be evaluated with case study simulations.

This project will provide an improved understanding of the processes influencing the long-term effectiveness and fate of commercial particulate amendments for in situ treatment of mixed groundwater plumes. The findings will lead to an improved site management and decision making, specifically groundwater sites impacted with PFAS and hydrocarbons, by providing mechanistic insights on impacts of chemical, geochemical and microbiological factors on amendment’s sorption kinetics; long-term adsorption desorption capacity for amendments and identifying possible interferences. (Anticipated Project Completion - 2025).