PFAS forensics of drinking water sources

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent, toxic, and bioaccumulative compounds that are used in a variety of non-stick, water-proofing, and stain-resistant applications. PFAS have contaminated many water systems and pose a threat to drinking water supplies. Forensic techniques can be applied to identify potential PFAS contamination sources and inform the best possible water treatment options and selection of future municipal water sources. The Iowa Department of Natural Resources initiated a PFAS Action Plan in 2022 to sample Iowa surface and groundwaters. The testing results of this sampling have been analyzed to identify differences between the two water types. Among surface waters with detectable PFAS, the concentrations ranged from 2.0 – 49.0 ng/L, and from 1.8 – 419.6 ng/L for groundwater with detectable PFAS. The biggest distinction between surface water and groundwater was the distribution of PFAS subclasses; 87% of surface water samples contained no perfluoroalkyl sulfonic acids, indicating that aqueous film-forming foam (AFFF) contamination is not likely a major contributor to PFAS in Iowa surface waters. An implication is that surface water treatment plants in Iowa should prioritize PFAS treatment technologies that are most effective for perfluoroalkyl carboxylic acid removal. Each municipal drinking water well in the City of Ames was sampled and analyzed to identify its PFAS fingerprint. Well 17 had the most elevated PFAS concentration but showed significant concentration changes with differing well runtimes. Well 16, which is in close proximity to Well 17, contained a different PFAS fingerprint that clustered closely with the rest of the municipal wells, suggesting that the contamination experienced by Well 17 is isolated to only that well. PFAS fingerprints between the four Ames well fields were similar, suggesting similar, possibly diffuse, contamination sources over the Ames area. Surface water samples across Ames mostly had very low detections. Low PFAS concentrations were found in surface water close to Iowa State University campus, but the fingerprints were dissimilar to those of Wells 16 and 17. PFAS fingerprints based on diagnostic species indicated that AFFF may have impacted Well 17, and biosolids application may have impacted the Youth Sports Complex well field. The City of Ames wells can produce water for the Water Treatment Plant while complying with the proposed PFAS MCLs after Well 17 is omitted from the supply. Additionally, future wells can be established closer to surface waters without concern for PFAS impact due to low detections in those waters.