Overview
Vapor intrusion (VI) is the migration of volatile chemicals from the subsurface into indoor air. It is important to take VI processes into consideration where soil or groundwater is contaminated with volatile compounds and current or future land use scenarios suggest a potential human exposure pathway to indoor air.
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Process
Prior to initiating a VI evaluation associated with a Department of the Navy (DON) environmental release, it is important to confirm that chemicals in subsurface media are of sufficient volatility and toxicity to pose a potential VI concern and there is a potential complete human exposure pathway to indoor air. Assessing the VI pathway can be conducted at any point in the Environmental Restoration (ER) process (e.g., investigations, remediation, five-year reviews, etc.). The VI potential in existing buildings should be evaluated based on multiple lines of evidence (e.g., air, soil gas, distance to building, indoor sources, and building characteristics). Future VI potential should be assessed based on those lines of evidence that are applicable to reasonably anticipated future use.
At Environmental Restoration Program (ERP) sites where VI is occurring and posing an unacceptable risk to human health, the Remedial Project Manager (RPM) should make appropriate risk management decisions to mitigate the VI risk. Even if there is no current unacceptable VI risk, risk management decisions to address potential future VI risk may need to be further considered when a subsurface vapor source remains at a site.
The Department of Defense (DoD) Vapor Intrusion Handbook currently serves as DON’s guidance on VI. To ensure relevancy is maintained, handbook updates are issued as needed through a series of fact sheets prepared by the Tri-Service Environmental Risk Assessment Workgroup (TSERAWG). The TSERWG VI fact sheets can be accessed here. The Handbook uses a three-tiered approach to assess human health risks related to the VI pathway as follows:
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Tier 1 Screening Level Evaluation: To identify sites that warrant further VI consideration or determine VI is not a pathway of concern.
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Tier 2 Site-Specific Evaluation: To weigh multiple lines of evidence and refine the conceptual site model (CSM) for conclusions of VI occurrence (current VI in buildings) or potential to occur.
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Tier 3 Risk Management and Mitigation: If VI is occurring and posing an unacceptable risk, the RPM should make appropriate risk management decisions to mitigate the VI risk. In DON non-residential buildings, the RPM should collaborate and coordinate with DON Occupational Safety and Health professionals to identify unacceptable risk/exposures and potential exposure mitigation measures.
RPMs should also be aware of site-specific requirements as many states have developed or are in the process of developing their own VI guidance. It is important to keep in mind that not all state health agencies follow a tiered approach. RPMs should coordinate with their regulators to identify the technical approach that is most appropriate for their site. For more information, Chapter 13.6 of the DON Environmental Restoration Program Manual details VI management considerations.