Poly-and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foam (AFFF) are increasingly recognized as groundwater contaminants, though the composition and distribution of AFFF-derived PFASs associated with soils and subsurface sediments remain largely unknown. This is particularly true for zwitterionic and cationic PFASs, which may be incompletely extracted from subsurface solids by analytical methods developed for anionic PFASs. Therefore, a method involving sequential basic and acidic methanol extractions was developed and evaluated for recovery of anionic, cationic, and zwitterionic PFASs from field-collected, AFFF-impacted soils. The method was validated by spike-recovery experiments with equilibrated soil-water-AFFF and analytical standards. To determine the relative importance of PFASs lacking commercially available analytical standards, their concentrations were estimated by a novel semiquantitation approach. Total PFAS concentrations determined by semiquantitation were compared with concentrations determined by the total oxidizable precursor assay. Finally, the described method was applied to two soil cores from former fire-training areas in which cations and zwitterions were found to contribute up to 97% of the total PFAS mass. This result demonstrates the need for extraction and analysis methods, such as the ones presented here, that are capable of quantifying cationic and zwitterionic PFASs in AFFF-impacted source zone soils.

Soil and groundwater from an aqueous film-forming foam (AFFF)-impacted site were sampled at high resolution (n = 105 for soil, n = 58 for groundwater) and analyzed for an extensive list of anionic, zwitterionic, and cationic poly- and perfluoroalkyl substances (PFASs). Spatial trends for perfluoroalkyl acids and many precursors enabled a better understanding of PFAS composition, transport, and transformation. All PFASs without analytical standards were semi-quantified. Summed PFAS and individual PFAS concentrations were often higher at depth than near the surface in soil and groundwater. Zwitterionic and cationic compounds composed a majority of the total PFAS mass (up to 97%) in firefighter training area (FTA) soil. Composition of PFAS class, chain length, and structural isomers changed with depth and distance from the FTA, suggesting in situ transformation and differential transport. The percentage of branched perfluorooctane sulfonate increased with depth, consistent with differential isomeric transport. However, linear perfluorooctanoic acid (PFOA) was enriched, suggesting fluorotelomer precursor transformation to linear PFOA. Perfluorohexane sulfonamide, a potential transformation product of sulfonamide-based PFASs, was present at high concentrations (maximum 448 ng/g in soil, 3.4 mg/L in groundwater). Precursor compounds may create long-term sources of perfluoroalkyl acids, although many pathways remain unknown; precursor analysis is critical for PFAS fate and transport understanding.

The United States Environmental Protection Agency (USEPA) completed nationwide screening of six perfluoroalkyl substances in U.S. drinking water from 2013 to 2015 under the Third Unregulated Contaminant Monitoring Rule (UCMR3). UCMR3 efforts yielded a dataset of 36,139 samples containing analytical results from >5000 public water systems (PWSs). This study used UCMR3 data to investigate three aspects of per- and polyfluoroalkyl substances (PFASs) in drinking water: the occurrence of PFAS and co-contaminant mixtures, trends in PFAS detections relative to PWS characteristics and potential release types, and temporal trends in PFAS occurrence. This was achieved through bivariate and multivariate analyses including categorical analysis, concentration ratios, and hierarchical cluster analysis. Approximately 50% of samples with PFAS detections contained ≥2 PFASs, and 72% of detections occurred in groundwater. Large PWSs (>10,000 customers) were 5.6 times more likely than small PWSs (≤10,000 customers) to exhibit PFAS detections; however, when detected, median total PFAS concentrations were higher in small PWSs (0.12 μg/L) than in large (0.053 μg/L). Bivariate and multivariate analyses of PFAS composition suggested PWSs reflect impacts due to firefighting foam use and WWTP effluent as compared to other source types for which data were available. Mann-Kendall analysis of quarterly total PFAS detection rates indicated an increasing trend over time (p = 0.03). UCMR3 data provide a foundation for tiered design of targeted sampling and analysis plans to address remaining knowledge gaps in the sources, composition, and concentrations of PFASs in U.S. drinking water.

The ability to inoculate a PCE-NAPL source zone with no prior dechlorinating activity was examined using a near field-scale simulated aquifer. A known mass of PCE was added to establish a source zone, and the groundwater was depleted of oxygen using acetate and lactate prior to culture addition. An active and stable dechlorinating culture was used as an inoculum, and dechlorination activity was observed within 2 weeks following culture transfer. PCE reduction to TCE and cis-DCE was observed initially, and the formation of these compounds was accelerated by the addition of a long-term source of hydrogen (Hydrogen Releasing Compound). cis-DCE was the predominant chlorinated ethene present in the effluent after 225 days of operation, and production of VC and ethene lagged the formation of TCE and cis-OCE. However, dechlorination extent continued to improve over time, and VC eventually became a major product, suggesting that reinoculation was unnecessary. The detection of Dehalococcoides species in the source culture and in the simulated aquifer postinoculation indicated that the metabolic capability to dechlorinate beyond cis-DCE (t = 86 days and t = 245 days) was present. Elevated levels of TCE and cis-DCE were present in the source zone, but neither VC nor ethene were detected in the vicinity of NAPL. The results of this research indicated that adding dechlorinating cultures may be useful in the application of source zone bioremediation but that dechlorination beyond cis-DCE may be limited to regions downgradient of the source zone.

1,4-Dioxane (dioxane) is an emerging groundwater contaminant that has significant regulatory implications and potential remediation costs, but our current understanding of its occurrence and behavior is limited. This study used intensive data mining to identify and evaluate >2000 sites in California where groundwater has been impacted by chlorinated solvents and/or dioxane. Dioxane was detected at 194 of these sites, with 95% containing one or more chlorinated solvents. Dioxane frequently co-occurs with 1,1,1-trichloroethene (1,1,1-TCA) (76% of the study sites), but despite this, no dioxane analyses were conducted at 332 (67%) of the sites where 1,1,1-TCA was detected. At sites where dioxane has been identified, plumes are dilute but not large (median maximal concentration of 365 μg/L; median plume length of 269 m) and have been delineated to a similar extent as typically co-occurring chlorinated solvents. Furthermore, at sites where dioxane and chlorinated solvents co-occur, dioxane plumes are frequently shorter than the chlorinated solvent plumes (62%). The results suggest that dioxane has not migrated beyond chlorinated solvent plumes and existing monitoring networks at the majority of sites, and that the primary risk is the large number of sites where dioxane is likely to be present but has yet to be identified.