Abstract Characterizing the concentration and mass flux spatial distributions at sites with complex hydrogeologic conditions is critical to evaluate the fate and transport of contaminants, as well as to design effective remediation programs. PFAS (per‐ and polyfluoroalkyl substances)‐contaminated sites are even more complex due to the large number of compounds and their diversity in physicochemical properties. To aid in this effort, a high‐resolution passive profiler (HRPP), previously validated for measuring sediment porewater concentrations of chlorinated solvents, groundwater velocity, and geochemical parameters at high resolution (≤20 cm) was adapted to evaluate PFAS. The study location was a shallow (<5 ft. to water) aquifer at a site with historical AFFF (aqueous film‐forming foam) contamination. A discrete depth groundwater sampling system was used to obtain groundwater samples from specified depths (taken within 5 ft. of the HRPP installation locations) to compare to depth specific concentrations produced from the HRPP. Continuous cores were obtained from each HRPP installation location and HRPP were direct pushed into the borehole created during soil coring. Soil cores were field logged for soil texture. Five sets of HRPP strings ranging from 4 to 25 ft. below‐ground surface (BGS) were deployed and left to equilibrate for 28 d. HRPP and DPT (direct push technology) Geoprobe® Screen Point Sampling System (SP16)‐enabled discrete well samples were analyzed for concentrations of anions (Cl − , Br − , and SO 4 2− ) and subjected to PFAS target and suspect screening. The porewater concentration distributions of anions and targeted PFAS produced by the HRPP and SP16 methods were highly similar. Significant correlations were found at all sites with an r 2 of 0.76 for 23 targeted species quantified in both sample types ( P << 0.01, n = 1386). The HRPPs and paired SP16 targeted PFAS concentrations matched with 60% within a factor of 2 and 88% within a factor of 5. Some concentration distribution features captured by the HRPP were not captured by the SP16 samples due to a lack of resolution. Importantly, steep concentration gradients at the capillary fringe and other features around low permeability zones also were not accurately quantified by the SP16 but were captured by the HRPP. Anionic, cationic, and zwitterionic suspect screening species were correlated in paired depth HRPP and SP16 samples ( P << 0.01; n = 256 for anions, n = 258 for zwitterions, n = 188 for cations), although with anions the SP16 concentrations were generally higher. Overall, 29% of paired anion concentrations were within a factor of 2 and 85% within a factor of 5. These values were 38% and 89% for zwitterions, and 42% and 78% for cations, respectively. This work highlights the ability of the HRPP to produce accurate, high‐resolution concentration profiles of groundwater using direct drive devices, a major advantage in highly heterogenous systems and low permeability media.
Jackson et al. (Fri,) studied this question.
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