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

Topic Area: 7m. PFAS Site Characterization

Formatted Title:

Sorption and Recovery of PFAS for Design and Verification of Passive Flux Meters

Background/Objectives:

Passive flux meters (PFMs) have been developed and used to passively monitor the mass flux of site contaminants in an aquifer. PFMs are commonly filled with granular activated carbon (GAC) that adsorbs organic contaminants in groundwater when the PFM is deployed in a monitoring well. The GAC is also loaded with soluble tracers that are released from the PFM after deployment for calculating the Darcy velocity/groundwater flux (Hatfield et al., 2004; Annable et al., 2005). PFMs have been used to measure PFAS flux in groundwater at the Wurtsmith and Cannon Air Force Bases using the traditional GAC media and the 537 target-PFAS analysis methodology (Pohlmann et al., 2019; Adamson, 2020). However, the accuracy of PFMs to predict flux require contaminants to both readily absorb to the media and to be recovered by standard commercial extraction methodologies. Previous applications of PFMs to assess mass flux did not consider the variable sorption efficiency of long and short chain PFAS onto GAC nor the recovery efficiency of PFAS desorption from the GAC and may thus have underestimated the contaminant mass flux. This project includes a bench-scale study to better understand the usefulness and reliability of PFAS PFMs and has a clear objective to select an optimal PFAS sorbent to: (1) adsorb a wide range of PFAS effectively without desorption during PFAS PFM deployment; and (2) demonstrate optimal PFAS extraction method using organic solvents and/or brine solution for quantifying PFAS mass adsorbed on the sorbent.

Approach/Activities:

The benchtop portion of this study includes testing of sorption and then desorption of short and long chain PFAS-spiked control and groundwater on three sorbent media. A total of 27 test conditions plus 11 control conditions were proposed. Each test condition was tested in triplicates to verify data quality. The test conditions compared sorption and desorption of 10 PFAS onto three candidate sorbents: GAC (baseline), nonionic exchange resin (NIX) and regenerable IX (AIX). The 10 PFAS spiked onto sorbents ranged in concentrations from as low as 50 ppt to as high as 10 ppm (individually) in DI water and site collected groundwater and were assessed at up to three time steps to verify optimal deployment times. The sorbed PFAS on these three sorbents were later extracted using three different solvent/brine solutions. The PFAS recovery from the sorbents is determined by analyzing PFAS (Method 1633) in the liquid extract, PFAS residuals in the solid sorbent phase, and a comparison to spiked-PFAS loading rates. This bench-scale study is critical for the PFM design. The optimal sorbent, based on sorption and desorption capacity, will be selected to design a PFAS PFM that will be field tested at the Jacksonville, FL Naval Air Station in the second quarter of 2024.

Results/Lessons Learned:

This is the first comprehensive study with the goal of improving and verifying the design and use (i.e., deployment times) of PFMs for PFAS mass flux measurements. The selected sorbent will be based on both the ability of the sorbent to capture short and long chain PFAS as well as the ability to recover target analyte PFAS to increase the accuracy of PFAS mass flux measurements. Field results will be compared to traditional mass flux measurements obtained via hydraulic (slug) testing and Method 1633 groundwater analyses.

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Savannah Wunderlich Aiello