This project was conducted by a team of researchers from Naval Facilities Engineering and Expeditionary Warfare Center (NAVFAC EXWC), Geosyntec Consultants, Inc. (Geosyntec), and the University of California at Berkeley (UC Berkeley). The overall project goal was to demonstrate and validate the effectiveness of in situ thermally-enhanced low-pH persulfate oxidation of per- and polyfluoroalkyl substances (PFAS) via treatability studies and a field demonstration at an aqueous film-forming foam (AFFF) source area. The specific technical objectives of this project were as follows:
- Identify characteristics that make sites good candidates for this in situ treatment technology (Task 1);
- Work with Navy, Air Force, and the Strategic Environmental Research and Development Program (SERDP)/Environmental Security Technology Certification Program (ESTCP) to select a suitable demonstration site (Task 1);
- Leverage data from a Navy-led project to characterize PFAS at several field sites (ESTCP project ER-201633, “Characterization of the Nature and Extent of PFAS in Environmental Media at Department of Defense (DoD) Sites for Informed Decision-Making”) (Task 2);
- Conduct site-specific treatability studies and modeling using site soil and groundwater samples to inform design parameters for the field demonstration (Task 3);
- Conduct a field demonstration consisting of several stages to acidify and heat the aquifer and to deliver persulfate oxidant throughout the treatment zone, followed by groundwater extraction and granular activated carbon (GAC) treatment (Task 4); and
- Develop technical guidance that can be posted on ESTCP’s website and distributed to assist with technology transfer (Task 5).
Site-specific treatability studies were conducted to validate the performance of a promising destructive treatment technology for PFAS that could be conducted in situ: thermally-enhanced persulfate oxidation at low pH. Because this technology is not expected to be fully effective in destroying all PFAS (i.e., perfluorooctane sulfonate [PFOS] and similar perfluorosulfonic acids), the technology would need to be used in combination with pump-and-treat to fully address a mixed PFAS source zone.
After carefully reviewing the characteristics of several potential demonstration sites, the project team recommended Naval Air Station (NAS) Jacksonville former fire training area FT-02 as the demonstration site.
Due to additional funding needed to complete the field demonstration, the field demonstration portion of the project was not conducted.
The laboratory treatability studies were conducted to facilitate the design of the field demonstration. The primary objectives of the laboratory treatability studies were to assess the feasibility and efficacy of treatment including the use of hydrogen peroxide for aquifer heating, persulfate acidification and treatment of perfluorocarboxylic acids (PFCAs) and PFCA precursors at low pH, and neutralization of the aquifer following treatment. Key results and implications are as follows:
- Baseline characterization: Naval Air Station (NAS) Jacksonville was determined to be a good candidate for a field demonstration. The site has high PFAS concentrations (~0.8 mg/L PFCAs and 2.2 mg/L perfluorosulfonic acids [PFSAs]), low alkalinity/buffering capacity, low salinity, and low concentrations of leachable metals following pH reduction during in situ chemical oxidation (ISCO). NAS Jacksonville groundwater has high dissolved organic carbon (DOC) and filterable substance that inhibited PFCA destruction rates, resulting in a higher persulfate dose to effectively treat PFCAs.
- Peroxide heating: Laboratory batch tests did not indicate any obvious barriers to injecting peroxide to generate heat within the treatment area at NAS Jacksonville. Pseudo-first order rate constants for hydrogen peroxide degradation for 0.1, 1.0, and 12% peroxide were determined to be 1.88 ± 0.08 day-1 , 0.83 ± 0.04 day-1, and 0.78 ± 0.05 day-1, respectively. Additions of 5 mM ferric sulfate and 10 mM sodium citrate to 12% peroxide groundwater/soil samples reduced the rate constant to 1.26 ± 0.06 day-1. Peroxide treatment transformed some precursor compounds to PFCAs.
- Persulfate acidification and treatment: Persulfate treatment achieved >90% destruction of PFCAs and PFCA precursors in groundwater batch tests, using a single dose of 500 mM persulfate. In groundwater/solids slurry, >90% destruction of PFCAs and PFCA precursors was slower and required multiple persulfate additions. Pretreatment using 12% peroxide was followed by weekly 200 mM persulfate additions over 35 days to achieve >90% destruction. Final TOP assay results confirmed the destruction of PFCA precursors and soil extraction confirmed negligible PFCA adsorption to solids. Although dose and concentration requirements are on the high end of typical field doses for other contaminants, resulting in higher chemical reagent costs and lengthier field demonstration, there are no anticipated barriers for field application.
- Neutralization: Neutralization experiments demonstrated the result of adding an excess of CaCO3 in solid form to post-treatment samples, following peroxide-persulfate experiments. CaCO3 addition raised the pH from 1 to about 3 and then adding <50 µL 4 M NaOH into a 1 mL sample was sufficient to raise the pH to 6. Dissolved metals concentrations decreased significantly with the pH increase, likely due to metal precipitation, although chromium and selenium concentrations still exceeded MCLs. Results will inform our expectations and design of post-treatment aquifer neutralization. In summary, laboratory study results have informed the design of the field demonstration including the feasibility and dose of peroxide, peroxide stabilizer, dose of persulfate, need for a buffer solution, persulfate treatment duration, and the effect of neutralization.
This non-proprietary technology is aligned with DoD’s preference for in situ remediation and aggressive mass reduction to accelerate site closure. As a public domain technology, it could lead to significant cost savings over proprietary methods. It could improve the sustainability of existing pump-and-treat systems, saving decades of system operation and cost.
Only the treatability assessment portion of this project was completed due to cost issues.