PFAS Q&A: PFAS Vapor Intrusion – What You Need to Know

PFAS vapor intrusion is an emerging area of PFAS science that looks at the migration of PFAS from contaminated subsurface soil or groundwater into indoor air. Despite some PFAS having low volatility, research suggests that volatile and semi-volatile PFAS may create a vapor intrusion pathway under certain conditions and pose human exposure risks.

Below, Langan answers questions about whether PFAS can move from the subsurface into indoor air, what current research does and doesn’t tell us, and how to approach the pathway responsibly on active projects.

Key Takeaways

• PFAS has the potential to move from contaminated soil or groundwater into indoor air under certain conditions, creating a vapor intrusion pathway.
• PFAS vapor intrusion is possible, but not all PFAS are likely to contribute to a vapor intrusion pathway. Certain volatile and semi-volatile PFAS are more dangerous than PFOA and PFOS compounds.
• There are currently no established screening levels or regulatory compliance standards for PFAS vapor intrusion, making careful site-specific evaluation important.
• PFAS vapor sampling requires coordination with specialty laboratories, careful method selection, and data transparency.

Can PFAS cause vapor intrusion?

Potentially, but only for a subset of the PFAS family. Most of the PFAS compounds that dominate regulatory attention—PFOA and PFOS in particular—are ionic, have very low vapor pressure, and are not expected to volatilize from soil or groundwater in meaningful concentrations. However, PFAS includes thousands of chemicals. Neutral, volatile, or semi-volatile PFAS, including certain ultrashort-chain compounds and fluorotelomer alcohols (FTOHs), have physical and chemical properties mirroring the chlorinated solvents that drive traditional vapor intrusion (VI) concerns. EPA-led research has detected these vapor-forming PFAS in soil gas, sub-slab soil gas, and groundwater at contaminated sites, confirming that a pathway can exist under the right conditions. What isn’t yet established is how common, predictable, or significant that pathway is across different site types.

How do you integrate PFAS into a traditional vapor intrusion evaluation?

PFAS should be evaluated as a supplemental line of inquiry rather than a wholesale replacement of the VI framework. A conventional VI conceptual site model already accounts for source characterization, contaminant fate and transport through the vadose zone, and pathways into occupied structures, all of which also apply to PFAS. The differences appear in the details: identifying whether PFAS present at a site include volatile or semi-volatile species, adapting sampling protocols since standards for vapor-phase PFAS in soil gas and indoor air are not finalized, and interpreting results without agreed-upon screening levels. Langan approaches these details on a site-specific, weight-of-evidence basis rather than making PFAS VI-related assumptions at every PFAS-impacted property. Considerations include the specific PFAS present, site geology, building characteristics, and volatile organic compounds (VOC) or other VI data.

Are there indoor air screening levels or regulatory standards for PFAS vapor intrusion?

No, and that is one of the biggest practical challenges right now. Regulators generally acknowledge that the pathway is biologically and physically plausible but have stopped short of mandating routine PFAS VI investigations, in part because sampling and analytical methods aren’t yet standardized. Some states have begun incorporating PFAS considerations into Phase I Environmental Site Assessments under ASTM E1527-21, but that framework covers due diligence and soil/groundwater sampling, not VI screening.

What are the biggest hurdles for PFAS vapor intrusion investigations?

There isn’t a standardized, widely validated method for measuring vapor-phase PFAS across soil gas, sub-slab soil gas, and indoor air, which is a significant practical constraint compared to VOC VI work. Laboratories and researchers are refining thermal desorption GC/MS/MS methods for compounds like FTOHs, and some target analytes are prone to interference from related PFAS breakdown products during analysis. Detection limits, sample media compatibility, and holding times are still being worked out. In practice, this means PFAS vapor sampling programs require close coordination with specialty laboratories, careful method selection based on the specific compounds of concern, and transparency about the limitations of current data.

How does Langan help clients navigate PFAS vapor intrusion issues?

Langan’s PFAS team brings extensive experience in PFAS investigation and remediation, complemented by decades of expertise in traditional VI assessment and mitigation. That combination matters because PFAS VI doesn’t have its own playbook yet, so teams must understand both the emerging PFAS science and the practical realities of building-specific vapor pathways.

With regulatory and scientific requirements for PFAS VI still evolving, Langan’s role is as much about helping clients make informed decisions as it is about executing sampling and remediation once a pathway is confirmed. Clients working through PFAS-impacted sites, whether in a transaction, litigation, or active remediation context, can contact Langan’s PFAS experts to discuss site-specific strategies.

Mukta Patil is an Associate in Langan’s San Jose office with over 15 years of experience in environmental engineering. Her expertise encompasses environmental issues, waste disposal assessments, oil and chemical cleanup, vapor mitigation design, and other remediation issues. She is also adept at laboratory techniques and analytical methods for environmental pollutants.

_{This content reflects the state of PFAS vapor intrusion science and guidance as of mid-2026, including the ITRC December 2025 PFAS Vapor Intrusion Fact Sheet and January 2026 VI Toolkit. As the field continues to evolve, Langan recommends confirming current regulatory requirements and screening guidance before finalizing site-specific investigation or mitigation strategies.}

PFAS and Vapor Intrusion FAQs

When should PFAS vapor intrusion be considered at a site?

PFAS vapor intrusion may need to be considered when investigation data suggests that volatile or semi-volatile PFAS could be present. The need for further evaluation should be determined on a site-specific basis.

What site conditions can affect PFAS vapor intrusion?

Potential PFAS vapor intrusion depends on the PFAS compounds present, site geology, building characteristics, and existing vapor intrusion data. These factors can help investigators determine whether a potential pathway requires further evaluation.

Does a PFAS-impacted property automatically require a vapor intrusion investigation?

No, because PFAS encompasses thousands of compounds with different physical and chemical properties, the presence of PFAS does not necessarily mean that there is a vapor intrusion pathway. Site history and the specific PFAS present will inform whether further evaluation is required.

Can PFAS vapor intrusion impact property transactions or due diligence?

PFAS vapor intrusion may become a consideration when evaluating PFAS-impacted properties as part of environmental due diligence. Since the science and regulatory landscape are still evolving, potential vapor pathways may need to be evaluated based on the circumstances of the individual property.