Formatted Title
In Situ Sorption of PFAS Using Colloidal Activated Carbon
Background/Objectives
Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have impacted groundwater at a variety of sites largely through their use in aqueous film-forming foams (AFFF). At AFFF-impacted sites, PFAS transport into the soil, vadose zone, and groundwater has been observed. AFFF constituents have been detected in shallow soils years to decades after their use was terminated, indicating the persistence and recalcitrance of many of these chemicals. Because PFAS are both highly recalcitrant and mobile, impacted groundwater continues to expand, potentially further increasing the number of impacted locations and the overall treatment costs.
While ex situ treatment approaches are progressing and full-scale systems are currently operational, there are currently no proven in situ approaches to treat PFAS in groundwater. One potential approach is the application of colloidal activated carbon (CAC) for in situ sorption of PFAS within impacted aquifers. Even though this technology is currently being used for the in situ treatment of other chemicals of concern, there are several questions about using this amendment in situ for PFAS. This includes distribution in aquifers; general effectiveness on different molecular structures comprising PFAS; and the long-term adsorption capacity and potential for re-release of PFAS to groundwater
Approach/Activities
A demonstration of this technology via a barrier approach is currently being conducted at a PFAS-impacted DoD site in the mid-Atlantic region. Demonstration activities have included site characterization, laboratory column studies, CAC injection and distribution testing, and long term monitoring of effectiveness. Bench-scale treatability testing was completed at the APTIM Biotechnology Development and Applications Group (BDAG) laboratory using PFAS-impacted site materials from the site. The information obtained was used to inform design and other considerations for field-scale implementation.
Results/Lessons Learned
The goal of this effort is to validate an in situ PFAS sorption approach using CAC. Batch treatability testing with site sediments and groundwater showed robust CAC distribution and sorption performance. The project then moved to the field where CAC was injected in a barrier approach with a target concentration of 2,000 mg carbon/kg soil. Five quarters of post-injection monitoring have been performed so far with at least 98 percent reduction in total PFAS at the downgradient edge of the barrier in shallow and deep wells. The sorptive performance of individual PFAS (including short chains) will be presented and discussed, as well as other performance monitoring tools that have also been used.