Per- and Polyfluoroalkyl Substances in Field-Collected Light Non-Aqueous Phase Liquids

Abstract

Per-and polyfluoroalkyl substances (PFAS) and non-aqueous phase liquids (NAPLs) co-occur at sites where aqueous film forming foams (AFFFs) were used as part of firefighter training exercises or in response to emergencies (e.g., crashes). Till date, there are no data on PFAS in field-collected, light NAPLs (LNAPLs) recovered from groundwater wells on US military bases. Analytical methods were developed for target and suspect nonvolatile (anionic) and volatile (neutral) PFAS in field-collected LNAPLs. The validated methods were demonstrated on 17 LNAPL samples collected from the subsurface at five military installations with known AFFF impacts and where LNAPL releases date 10−70 years ago. Target and suspect anionic PFAS associated with AFFF of either electrochemical fluorination or fluorotelomerization origin were quantified and semi-quantified, respectively, in 11 LNAPLs. Perfluorooctane sulfonate (PFOS) occurred at the highest frequency, ranging from 110 to 11,100 ng/L. As a class, perfluoroalkyl sulfonamides occur at a frequency similar to that of PFOS, but at higher concentrations, with the C6 homolog ranging up to 67,500 ng/L. Only one LNAPL had quantifiable neutral PFAS (6:2 fluorotelomer alcohol), indicating potential biotransformation and/or volatilization. Residual LNAPLs at AFFF-impacted field sites may represent an undetected reservoir of PFAS that must be considered when designing remedial actions.

Research Needs Regarding the Vapor Intrusion Potential of Volatile Per- and Polyfluoroalkyl Substances

“…Similarly, the surfactant behavior of PFASs could impact their distribution among phases throughout the vadose zone also. How does the co-occurrence of other contaminants (e.g., other AFFF components, solvents) modify the accumulation of FtOHs, FOSAs, and FOSEs at the groundwater table, which could impact the availability of vapor-phase PFASs in soil gas in source zones and down-gradient locations? Christie et al reported data demonstrating that certain PFASs were present in less-dense-than-water non-aqueous phase liquids (LNAPLs) that were recovered from groundwater wells on US military bases where AFFFs were used. Whereas “only one had quantifiable neutral PFAS (6:2 fluorotelomer alcohol)” in their study, it is conceivable that such LNAPLs influence the volatilization of a variety of PFASs into overlying soil at other sites where AFFFs were used.…”

“…Christie et al 36 reported data demonstrating that certain PFASs were present in less-dense-than-water non-aqueous phase liquids (LNAPLs) that were recovered from groundwater wells on US military bases where AFFFs were used. Whereas "only one had quantifiable neutral PFAS (6:2 fluorotelomer alcohol)" in their study, 36 it is conceivable that such LNAPLs influence the volatilization of a variety of PFASs into overlying soil at other sites where AFFFs were used. Titaley et al 9 noted that the impacts of butyl carbitol, a relatively abundant component of certain AFFFs, on biotransformation of FtOHs "are not known and represent a knowledge gap".…”