Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have become widespread in groundwater through their use in aqueous film forming foams (AFFFs). The DoD and civilian airports have used PFAS-containing AFFFs extensively during fire fighter training exercises and for battling hydrocarbon (e.g., jet fuel) fires. Because PFAS are both highly recalcitrant and mobile, 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 (primarily granulated activated carbon [GAC] systems added to existing pump-and-treat infrastructure), there are currently no validated in situ approaches to treat PFAS in groundwater. The primary objective of this ESTCP project is to demonstrate and validate the field application of colloidal activated carbon for in situ sequestration of PFAS in source area groundwater, thus mitigating plume expansion.

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 [PAC and CAC], organoclays, biochar) are now being proposed and some are being applied in the field as sequestering agents for PFAS in soils and/or groundwater aquifers. While in situ sequestration of PFAS via the injection of CAC is a very promising treatment approach, the technology has not received the necessary independent scientific scrutiny to determine (1) distribution of amendments in aquifers; (2) general effectiveness on different molecular structures comprising PFAS; (3) long-term adsorption capacity and potential for rerelease of PFAS; (4) impacts and/or joint remedial potential for chlorinated solvents or hydrocarbons in conjunction with PFAS; and (5) potential detrimental effects, such as transport of CAC into local monitoring wells. There is a clear need to provide objective field data concerning the above questions to help advance future applications of adsorptive amendments, and CAC in particular, as a mature in situ PFAS treatment technology. In that the injection of CAC represents one potential technique to treat source areas, mitigate plume expansion, and reduce costs at PFAS sites that can be applied immediately, research concerning its true effectiveness at field scale is of critical importance.

This project will provide DoD with an independent, objective evaluation of the effectiveness of CAC for the long-term, in situ sequestration of PFAS in groundwater aquifers. This type of evaluation is currently lacking. The field demonstration is also expected to provide guidance on the potential to utilize this technology for joint sequestration/treatment of co-occurring chemicals, such as chlorinated solvents in conjunction with PFAS, and the impact of those chemicals on CAC effectiveness and longevity in an aquifer. In that there are currently no proven in situ remedies for PFAS destruction or sequestration, understanding the benefits and limitations of this technology is of critical importance.