Aqueous film foaming foams (AFFF) were widely used at DoD installations for fire fighter training exercises and fire response. Due to their stability at high temperature and amphiphilic properties (i.e., polar and non-polar moieties), these forms contain mixtures of per- and polyfluoroalkyl substances (PFASs), including PFOA and PFOS. Additionally, chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE), were commonly used for aircraft engine cleaning, paint removal, and degreasing metal parts. As a result of improper containment and accidental releases, contaminated groundwater plumes at DoD sites often contain mixtures of chlorinated solvents and PFASs, both of which have stringent drinking water standards.
The U.S. EPA has established a maximum contaminant level (MCL) of 5 ppb (μg/L) for PCE and TCE, while provisional drinking water health advisories of 70 ppt have been set for PFOA and PFOS, individually or combined. Although bioremediation is commonly used to treat PCE and TCE, PFOS is extremely recalcitrant to conventional thermal, chemical or biological treatment. Furthermore, PFOA and PFOS were recently shown to inhibit microbial reductive dechlorination of TCE. Thus, the goal of this project is to develop sequential or “treatment train” in situ remediation approaches, in situ barrier walls and recirculating wells coupled with biological processes, to effectively treat groundwater plumes containing mixtures of PFASs and chlorinated ethenes and to understand the potential synergies associated with these combined remedies.
To achieve the project goals, the research approach is structured around three integrated tasks that are designed to:
- Develop and test highly reactive materials capable of degrading and/or sequestering PFASs and chlorinated ethenes (e.g., PCE, TCE, cis-dichloroethene, vinyl chloride).
- Develop biological systems to treat chlorinated ethene (e.g, PCE, TCE, cis-dichloroethene) and PFAS reaction byproducts following sorptive and reactive treatment (Task 1), respectively.
- Evaluate the treatment performance of the combined physicochemical and biological systems developed in Tasks 1 and 2, implemented as reactive barrier walls and downhole recirculating wells using groundwater containing mixtures of PFAS and chlorinated ethenes (Task 3).
The reactive systems developed in Tasks 1 and 2 will be combined into two different types of in situ treatment systems, reactive barrier walls and downhole recirculating wells. The reactive barrier wall approach has the advantage of being an adaptation of an existing in situ technology, but there are drawbacks with respect to material lifespan and replacement or regeneration of the barrier wall. The downhole recirculating systems will draw contaminated water into a reactive chamber at a specified depth interval. The latter system offers the ability to easily replace the reactive material and the flexibility to utilize downhole light sources (e.g., LED) to catalyze reactions.
This project will develop combined in situ remediation technologies designed to treat contaminated groundwater containing mixtures of PFASs and chlorinated ethenes, and the corresponding rate parameters and treatment capacities of each system. The novel aspects of these systems include (a) treatment of PFOS, which has not been degraded in situ using either biological or chemical methods, (b) treatment of co-mingled PFASs and chlorinated solvents, and (c) characterization and treatment of PFAS reaction byproducts. (Anticipated Project Completion - 2020)