Remediation of PFAS-impacted sites is a formidable challenge due to the complex mixture of hundreds of PFASs present in aqueous film-forming foams (AFFF), limitations of analytical capabilities, low (part per trillion) levels of concern in the environment, and inherent stability of many perfluoroalkyl substances including perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).
The goal of this project is to evaluate the efficacy of 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 PFCAs (i.e., polyfluoroalkyl substances that are known PFCA precursors and degrade slowly over time in the environment to form PFCAs). The technology is not expected to oxidize PFOS and other perfluorinated sulfonic acids (PFSAs). Hence, the in situ persulfate oxidation will be paired with pump-and-treat using GAC sorption. Pre-treatment using in situ persulfate oxidation would remove source area mass to the extent practicable and may decrease life-cycle costs and duration of pump-and-treat.
Geosyntec's Scope of Services
Geosyntec teamed with the United States Navy and researchers at the University of California, Berkeley to conduct this applied research project. Geosyntec led several key pre-demonstration tasks including review of site investigation data, selection of a suitable demonstration site, and 3D modeling to evaluate heat flow and oxidant consumption using data from site-specific treatability studies. The team led the process of designing peroxide injections for subsurface heating, and delivery of persulfate and other reagents. The team also designed an ex situ treatment system consisting of pH neutralization, precipitation and filtration, and GAC sorption followed by reinjection of treated groundwater. Geosyntec plans to implement the field demonstration beginning in Fall 2018.
This ESTCP project is the first full-scale field demonstration of an in situ remediation technology for PFASs. Significant accomplishments and expected benefits for DoD 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.