What Is Vapor Intrusion?
Vapor intrusion occurs when volatile chemicals in soil or groundwater migrate upward as vapors and enter buildings through cracks, utility conduits, or other openings. It is a growing concern for property owners, facility managers, and developers, especially at older industrial sites, brownfields, dry cleaners, and former manufacturing properties.
As more states adopt strict guidance under the U.S. Environmental Protection Agency’s vapor intrusion framework and ASTM E1527-21, understanding this issue is essential for maintaining compliance and protecting occupants.
How Vapor Intrusion Happens
Vapor intrusion begins when volatile compounds evaporate from contaminated soil or groundwater. These vapors migrate upward, typically following the path of least resistance.
Common pathways include:
- Cracks in foundations or concrete slabs
- Gaps around utility lines and pipes
- Sump pumps and floor drains
- Elevator shafts and utility trenches
- Wall cavities and crawlspaces
Once inside, vapors can collect at levels that pose potential health risks or trigger regulatory action.
Common Contaminants Associated With Vapor Intrusion
Volatile organic compounds (VOCs) are the primary drivers of vapor intrusion. These include:
- Trichloroethylene (TCE)
- Tetrachloroethylene (PCE)
- Benzene, toluene, ethylbenzene, and xylene (BTEX)
- Petroleum hydrocarbons from leaking tanks
- Chlorinated solvents from degreasing operations
- Petroleum additives and oxygenates such as MTBE
These compounds volatilize easily and can travel long distances underground, making early detection critical.
Why Vapor Intrusion Is a Growing Regulatory Priority
Regulators increasingly require vapor intrusion evaluations as part of:
- Phase I and Phase II Environmental Site Assessments
- Brownfield redevelopment planning
- Real estate transactions involving former industrial properties
- Risk assessments for existing manufacturing operations
- Remedial action plans for contaminated sites
Many state agencies have lowered screening levels for VOCs, meaning even small concentrations can trigger additional testing or mitigation. Health-based screening values often focus on chronic exposure risks, carcinogenic potential, developmental and reproductive impacts, and sensitive populations such as children or hospital occupants.
Signs You May Have Vapor Intrusion
While vapor intrusion is not always detectable without testing, certain conditions raise the likelihood:
- Past spills of solvents or petroleum products
- Historical dry-cleaning operations
- Underground storage tank failures
- Documented groundwater contamination near or on the property
- Strong chemical odors in basements or utility rooms
- Elevated levels of VOCs detected during air monitoring
Even if no obvious signs are present, regulatory requirements may still mandate evaluation.
How Vapor Intrusion Is Assessed
Assessing vapor intrusion typically involves a multi-step investigation.
Review of site history and previous environmental data: Evaluators review spill reports, tank records, groundwater monitoring data, historical land uses, and regulatory databases to establish a baseline understanding of potential vapor sources.
Soil gas and sub-slab sampling: Samples are collected directly from beneath building foundations, providing data for risk evaluation.
Indoor and outdoor air sampling: Indoor air sampling assesses real-time conditions within the building, while outdoor samples help distinguish background conditions from building-specific vapor sources.
Data interpretation and risk assessment: Collected data is compared to state and federal screening values. Risk-based models help determine whether mitigation is needed.
Vapor Intrusion Mitigation Options
If vapor intrusion is confirmed or poses a potential risk, mitigation measures may include:
- Sub-slab depressurization systems (SSDS) that create negative pressure beneath the slab to prevent vapors from entering the building
- Vapor barriers installed beneath new building foundations or during renovations
- Sealing major cracks and utility penetrations to reduce infiltration pathways
- Ventilation enhancements to increase air exchange rates and dilute VOC concentrations
- Source removal or remediation to address contamination directly through soil excavation, groundwater treatment, or chemical oxidation
Impacts on Property Transactions and Redevelopment
Vapor intrusion can significantly influence property value, lender requirements, insurance considerations, redevelopment timelines, and occupancy approvals. Increasingly, lenders and regulators require vapor intrusion clearance before approving development projects on former industrial or commercial sites.
How O6 Environmental Supports Vapor Intrusion Assessments
O6 Environmental provides full-service support for vapor intrusion evaluation and mitigation, including:
- Sub-slab and soil gas sampling
- Indoor and ambient air testing
- Risk assessments and regulatory reporting
- Design and installation of sub-slab depressurization systems
- Long-term monitoring programs
- Coordination with state and federal regulatory agencies
Our team ensures that facilities remain compliant while protecting occupants and future site users.
A Critical Component of Site Safety and Compliance
Vapor intrusion is one of the most important environmental concerns facing industrial and commercial properties today. With increasing regulatory scrutiny and potential health impacts, proactive assessment is essential.
O6 Environmental helps facility managers, developers, and property owners address vapor intrusion risks with proven, compliant, and cost-effective strategies.
