New scientific findings and updated federal and state regulatory guidance on vapor intrusion are prompting facility leaders to reassess indoor air quality and risk management, especially on redeveloped or legacy sites. Vapor intrusion involves harmful chemical vapors migrating from contaminated soil, groundwater, or infrastructure into buildings, posing previously underestimated health risks.
Due Diligence and Permitting Challenge
Facilities previously deemed low risk may face renewed scrutiny, especially when property use changes. Investors and ESG teams increasingly demand compliance with current vapor intrusion standards, expanding risk management beyond previously acceptable environmental standards. Traditional assessments that rely on attenuation factors may now be considered insufficient.
What’s Changing?
Beyond slab cracks, recent studies reveal that municipal infrastructure, such as sewers and utility conduits, can serve as preferential vapor pathways, allowing contaminants to bypass soil attenuation and enter indoor spaces at higher concentrations.
Temporal variability affects exposure. Vapor intrusion levels fluctuate with temperature, pressure, and wind speed, as well as with building conditions related to occupancy, heating, and cooling. This can lead to short-term spikes that may be missed by limited sampling, underscoring the value of continuous indoor air monitoring.
Federal and multiple state agencies have revised vapor intrusion guidance, lowering screening levels and emphasizing multiple lines of evidence, including sewer sampling and seasonal variability, which may reopen closed sites or impose stricter reviews.
Some preferential pathways can bypass traditional soil-gas modeling. There is a shift toward indoor air sampling and sub-slab soil gas data over predictive modeling, which recent studies suggest may underestimate risk.
Many states, such as Washington and California, have adopted more stringent short-term (acute) screening levels for Trichloroethylene due to developmental toxicity concerns.
Proven Strategies That Work
Understanding a site’s history and conducting early vapor intrusion screening enables the integration of mitigation into building design or tenant improvements, reducing retrofit costs, operational disruptions, and liability. Delayed assessments often lead to costly last-minute interventions.
There are proven mitigation strategies available. Effective vapor intrusion controls include sub-slab depressurization systems, sealing entry points, and addressing sewer or other utility-related pathways through venting or lining. Proper design, installation, and monitoring are crucial for sustainable operational success and tenant health.
Ms. Barrow recommends facility actions in response to expanding regulations, including:
About Our Author: Alissa Barrow, P.E., QISP, is an environmental engineer specializing in environmental assessment, remediation, and compliance, with a focus on vapor intrusion evaluation and mitigation. Ms. Barrow has managed complex projects involving vapor intrusion risk assessments, soil and groundwater investigations, and remediation technologies, including vapor intrusion mitigation systems, sub-slab depressurization systems, soil vapor extraction, situ chemical oxidation, and high-vacuum dual-phase extraction. Her expertise and successful track record over a decade ensure regulatory compliance while sustaining development goals, leading to timely delivery and cost savings.
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