The remediation of sites impacted by per- and polyfluoroalkyl substances (PFAS) is a formidable challenge due to the complex mixture of hundreds of PFAS present in aqueous film-forming foams (AFFF), a major source of PFAS in the environment. Other treatment challenges include low (part per trillion) levels of concern, complexity of PFAS transformations, limited analytical capabilities, and the inherent stability of many perfluoroalkyl substances including perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The current best available technologies, pump-and-treat using granular activated carbon (GAC) or ion exchange, are expensive and require long timeframes; developing a less costly in situ option would be a significant breakthrough.
The goal of this ongoing project is to evaluate the efficacy of using in situ thermally-enhanced persulfate oxidation to degrade PFOA and other perfluorinated carboxylic acids (PFCAs), as well as a significant "hidden" long-term source of known PFCA precursors that degrade slowly over time in the environment to form PFCAs. The technology is not expected to oxidize PFOS and other perfluorinated sulfonic acids (PFSAs), so in situ persulfate oxidation would need to be paired with groundwater extraction and ex situ treatment. Using in situ persulfate oxidation in the source zone prior to pump-and-treat would remove source area mass to the extent practicable and may decrease life-cycle costs and duration of treatment.
Geosyntec's Scope of Services
Geosyntec teamed with researchers with the U.S. Navy and the University of California, Berkeley to conduct this applied research project. We led several key pre-demonstration tasks including review of site investigation data, selection of a suitable demonstration site, 3D modeling to evaluate heat flow and oxidant consumption using data from site-specific treatability studies, and development of a draft demonstration plan. The team led the process of evaluating various subsurface heating technologies and delivery methods for persulfate and other reagents. The team also prepared a conceptual design of an ex situ treatment system consisting of pH neutralization, precipitation and filtration, and GAC sorption followed by reinjection of treated groundwater.
This project demonstrates the effectiveness of an in situ remediation technology for treating PFAS. Significant accomplishments and expected benefits for the owners of sites impacted by PFAS include the following:
- Demonstrated conversion of dozens of polyfluorinated compounds with largely unknown fate and transport characteristics to a small suite of compounds with better known characteristics, eliminating a long-term source of PFOA and simplifying future monitoring programs
- Enhanced mass removal of PFOA and other PFCAs via flushing and oxidation and enhanced mass removal of PFOA and other PFSAs via pH adjustment and thermal desorption
- Field basis (i.e., technology design parameters, performance data) for evaluating life-cycle costs and treatment timeframes and overall recommendations for treating PFAS precursors at pump-and-treat sites.