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Vapor Intrusion

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.


Jump to Resources to access Policies & Guidance, Publications, Related Sites, and Tools

 

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: 
 

  • Tier 1 Screening Level Evaluation: To identify sites that warrant further VI consideration or determine VI is not a pathway of concern.

  • 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.

  • 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.

 

 

RESOURCES

Topics

Title and Description

ERP Manual

DON Environmental Restoration Program Manual: Chapter 13.6 Vapor Intrusion (February 2018)

Defines VI and describes the guidance and policies available to RPMs to evaluate the VI pathway based upon multiple lines of evidence.

Petroleum VI

Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites (2019)

This EPA guidance specifically focuses on VI from petroleum sources. It provides screening criteria based on physical separation distances between vapor sources and potential receptors based on data specific to leaking underground storage tank (UST) sources.

Mitigation

Indoor Air

OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (June 2015)

 This technical guide presents current technical recommendations of the EPA based on the current understanding of vapor intrusion into indoor air from subsurface vapor sources. One of its main purposes is to promote consistency in assessing the vapor intrusion pathway. It provides a flexible science-based approach to assessment that accommodates the different circumstances (e.g., stage of the cleanup process) in which vapor intrusion is first considered at a site and differences among pertinent EPA programs

Risk Communication

NAVFAC/NMCPHC Guidance for Communicating Vapor Intrusion at Environmental Restoration Sites (October 2014)

Provides RPMs with recommendations for notifying and relaying information regarding VI investigations to Base personnel and potentially affected occupants of industrial, office, or residential buildings.

Background Chemicals

NAVFAC Interim Final Guidance for Environmental Background Analysis Volume IV: Vapor Intrusion Pathway (April 2011)

Reviews methodologies for assessing potential background sources to indoor air as a part of the assessment of the VI pathway.

DoD VI Handbook

DoD Vapor Intrusion Handbook (January 2009)

Outlines the process for the evaluation and investigation of the VI pathway at DoD sites.

VI Policy

Navy/Marine Corps Policy on Vapor Intrusion (April 2008)

Provides direction on the evaluation and remediation of the VI pathway. Topics covered include determining whether to evaluate the VI pathway for a site, planning and implementing a VI pathway evaluation, addressing background chemical issues, evaluating risk for human health exposures, evaluating remedial alternatives, and considering previously transferred property.

Background Chemicals

Navy Policy on the Use of Background Chemical Levels (January 2004)

Defines the DON position on consideration of background chemicals as applied to the DON ERP and clarifies the interpretation of EPA’s “Role of Background in the CERCLA Cleanup Program.”

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