Vapor, PFAS & evolving concerns

Some environmental questions need more than a review of surface conditions. The history of the source, the affected media, and the way people may be exposed all help define the appropriate investigation.

What is vapor intrusion?

Vapor intrusion occurs when vapor-forming chemicals in the subsurface migrate into a building. Evaluation considers the source, movement through soil or utilities, building conditions, and potential indoor exposure. A Phase I ESA may identify a concern, but confirming or evaluating the pathway can require separately scoped sampling and technical analysis.

Vapor encroachment and vapor intrusion

Vapor encroachment addresses the presence or likely presence of chemical vapors in the subsurface of a property. Vapor intrusion concerns their migration into indoor air. A screening conclusion about subsurface vapors is not an indoor-air risk assessment. Agree on the screening practice and any additional pathway evaluation in the scope.

How does PFAS fit into Phase I due diligence?

PFAS is a broad class, and regulatory status differs by compound and program. EPA designated PFOA and PFOS, including their salts and structural isomers, as CERCLA hazardous substances. These substances should not be dismissed as universally outside Phase I scope. Evaluate relevant use and release history; do not assume every PFAS compound has the same federal status.

Which histories can prompt a PFAS question?

Firefighting-foam use, certain industrial processes, waste handling, and documented releases can justify closer inquiry. A historical use is a screening clue, not proof that PFAS is present. Identify the likely chemicals and release mechanisms, review available records, and define whether further research or specialized sampling would answer the project’s question.

Related guidance

• Phase II ESA & targeted investigation

• Understanding your Phase I findings

• Property uses that deserve a closer look

Browse the Phase I ESA information hub

Discuss your property

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Primary references

• EPA · Vapor intrusion technical guidance

• EPA · PFOA and PFOS under CERCLA

General guidance does not replace a property-specific assessment. The applicable standard, regulations, scope, and available evidence govern the evaluation.