Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7f. In Situ PFAS Treatment Approaches

Formatted Title:

PFAS Behavior and Removal in a Zerovalent Iron Permeable Reactive Barrier

Background/Objectives:

As per- and poly-fluoroalkyl substances (PFAS) are being identified at historical Superfund sites, site practitioners have concerns that treatment approaches designed for co-contaminants may not be ideal remedies for PFAS reduction. An understanding of how PFAS interacts with established in situ technologies is necessary to determine the best course of treatment for the site as a whole. This project is evaluating PFAS behavior at sites with planned or existing in situ groundwater remediation systems that were designed to treat non-PFAS contaminants. One of these sites is a zerovalent iron permeable reactive barrier in Elizabeth City, North Carolina. The Elizabeth City ZVI PRB is one of the earliest full-scale PRBs in the United States. The PRB was constructed in 1996 to treat contaminated groundwater (trichloroethene, hexavalent chromium) originating from a metal plating shop. This site is also near an active runway so AFFF may also be present. The objectives of this study are to characterize any PFAS contamination present at this site and determine if the existing ZVI PRB is reducing PFAS contamination.

Approach/Activities:

The research includes collection of groundwater samples during in situ treatment to determine how treatment of TCE and chromium may have impacted concentrations of PFAS and its potential precursors. Targeted analysis of PFAS, as well as total organic fluorine and inorganic fluoride analysis, will enable the calculation of a PFAS mass balance during treatment. Literature review will illuminate potential removal mechanisms of PFAS by ZVI and specific sources for the PFAS contamination at this site.

Results/Lessons Learned:

Some of the key initial observations from this work include: 1) 14 PFAS compounds at the site were identified, predominantly long chain PFSAs; 2) PFAS and organic fluorine concentrations decreased by about 70% on average during monitoring events conducted over two years; 3) the PFAS plume is present at the same depths as the original chromium plume; 4) inorganic fluorine is increasing across the PRB about 11 times higher than organic fluorine is being lost; and 5) PFAS compounds present indicate potential sources of contamination are both AFFF and mist suppressants used for chromium metal plating. These observations suggest that the PRB may be at steady state and that PFAS removal may be due to adsorption followed by a long-term defluorination reaction. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.

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John Mason