USEPA’s PFAS vapor intrusion field test results: what to expect next

The results of field tests to evaluate the potential migration of per- and polyfluoroalkyl substance (PFAS) vapors from soils and groundwater into indoor air (i.e., PFAS vapor intrusion) were recently published in a report issued by the US Environmental Protection Agency (USEPA) and in the peer-reviewed literature.

Based on the results, USEPA concluded that “The vapor intrusion of volatile PFAS may pose health risks to building occupants and should, therefore, warrant consideration during vapor intrusion assessments at facilities where high concentrations are present in shallow soils and groundwater.”

In this article, we highlight what USEPA’s findings might mean for property owners, building occupants, and other stakeholders at sites where PFAS are present.

Over the past decade, the potential for vapors to migrate from subsurface soil or groundwater into the indoor air of buildings – a process commonly referred to as “vapor intrusion” (VI) – has become a routine element of many types of risk and liability assessments, particularly at sites with volatile chemicals such as chlorinated solvents. However, vapor intrusion has rarely been evaluated for PFAS due to the relatively low volatility and high solubility of the more common PFAS (such as PFOA and PFOS) and a historical focus on exposure to these compounds in drinking water and consumer products. However, USEPA has indicated that certain PFAS, such as fluorotelomer alcohols (FTOHs), may be sufficiently volatile to be of concern with respect to potential vapor intrusion.

In 2021, USEPA’s Office of Research and Development (ORD) announced that it was planning a study to evaluate the potential for PFAS vapor intrusion for the first time. Testing was conducted in 2021 and the results were published in November 2023.

USEPA conducted field tests including soil gas sampling for FTOH and perfluoroalkyl carboxylic acids (PFCAs), including PFOA, at two sites: a major fluorotelomer facility in New Jersey and a municipal landfill in Georgia. Indoor air sampling was not conducted at either site. While there was no evidence of PFAS vapor migration at the municipal landfill, USEPA concluded that the results at the New Jersey facility demonstrated that, “PFAS VI assessment is warranted at facilities where high PFAS concentrations are present or suspected in shallow soils and groundwater”.

However, several important questions remain unanswered. For example:

• USEPA states that vapor intrusion assessments are warranted where “high concentrations” of volatile PFAS are present (or even just “suspected”) in shallow soils and groundwater, but does not indicate what concentrations of PFAS in soil or groundwater might be considered sufficiently high to trigger a vapor intrusion assessment.
• USEPA concludes that vapor intrusion of volatile PFAS “may pose health risks to building occupants,” but has not issued toxicity values that would allow for an evaluation of such risks for any of the “volatile” PFAS detected in its tests (i.e., FTOHs).
• The USEPA detected PFCAs, including PFOA, in soil and sub-slab gas at the New Jersey site. However, the USEPA report notes that their testing indicates that migration of the PFCAs through the soil column appears to be in a particulate or moisture phase, rather than as a vapor.
• USEPA acknowledges that the test results do not confirm vapor intrusion as an exposure pathway and that “concurrent indoor air measurements would be needed to confirm a complete VI pathway.” However, volatile PFAS, specifically FTOH, from sources within buildings have been found to be “ubiquitous” in indoor air; such sources would need to be taken into account when assessing the possible contribution of vapor intrusion to indoor air measurements.
• Interpretation of the USEPA test results for the volatile FTOHs is complex. For example, only very low FTOH concentrations were detected in the shallow groundwater near the suspected source building, while high concentrations were detected in the sub-slab soil gas. Furthermore, when sample depth is considered, concentrations of the “primary” FTOH in soil gas and soil were generally higher in the sample locations farther from the presumed source area than at the location closer to the source area, while the reverse was true for the PFCAs and “secondary” FTOH.
• Commercially available analytical methods for PFAS using liquid chromatography followed by tandem mass spectrometric detection (i.e., LC/MS/MS), such as USEPA Method 537 Modified or Draft Method 1633, do not include FTOH as target analytes. To assess the presence of FTOH in indoor air, a separate analysis that uses gas chromatography and mass spectrometric detection (i.e., GC/MS/MS) may be needed. As shown in the USEPA study, detection limits for FTOH using GC/MS/MS are typically up to two orders of magnitude higher than for PFCAs using Method 537 Modified, further complicating an interpretation of results.

USEPA appears ready to require, or at least request, that PFAS vapor intrusion assessments, including the testing of indoor air, be conducted at some sites and facilities. However, the scope of such studies and how the results would be interpreted and used in decision-making is unclear.