Vapor Intrusion Technical Guidance

NOTE:     This page contains some relevant information on the development of EPD’s Vapor Intrusion Technical Guidance.  However, some of the information may be outdated since recent development of a draft guidance document. 

                Click the following link to access Download this pdf file. EPD’s Guidance for Evaluating the Vapor Intrusion Exposure Pathway


Contact: Amy Potter 404.524.0565 [email protected]


Vapor intrusion occurs when volatile compounds migrate from contaminated groundwater or soil into the indoor air of an overlying or nearby building (USEPA 2010).  The concern with vapor intrusion typically involves the potential for chronic health risks due to long-term exposure to relatively low vapor concentrations, although extreme cases can occur (e.g., explosion risks due to methane gas).  Emergency situations involving the risk of explosion or acute exposure to high vapor concentrations are beyond the scope of this webpage.  If you believe you are experiencing an indoor vapor emergency, take appropriate safety precautions (such as exiting the building) and contact your local fire department immediately.  For more basic information about vapor intrusion, click here.

The purposes of this webpage are to identify reference material to be used when evaluating the vapor intrusion pathway at sites regulated by the Georgia Environmental Protection Division (EPD) and to highlight EPD’s position on topics related to vapor intrusion. This webpage will be updated as new information becomes available.

EPD Contacts

For vapor intrusion questions related to a particular regulated site, stakeholders (e.g., property owners, consultants, attorneys, and the general public) should contact the specific EPD regulatory program overseeing the site.  The EPD compliance officer assigned to the site should be the first point of contact.  For EPD Land Protection Branch contact information by regulatory program, click here.

For general questions related to vapor intrusion, the following contacts are available by subject area:

EPD welcomes feedback from stakeholders regarding the content of this webpage. Please email suggestions and comments to [email protected] with “Vapor Intrusion Webpage Comments” as the subject.

Reference Documents

Current guidance from the United States Environmental Protection Agency (USEPA) consists of two primary documents:

Other useful documents may include:

In the event of conflicting information, preference will generally be given to the most recent USEPA documentation.

Assessment Tools

Vapor Intrusion Screening Level Calculator

USEPA has developed a spreadsheet that can be used to calculate risk-based media screening levels and target indoor air concentrations. The spreadsheet uses toxicity values from the USEPA Regional Screening Level Tables. 

Johnson and Ettinger Model

USEPA’s spreadsheet implementation of the Johnson and Ettinger model can be used for estimating indoor air risks from vapors originating from the subsurface.

Additional Considerations

Reporting Vapor Concentrations

EPD prefers that soil gas, sub-slab, and indoor air concentrations be reported in units of micrograms per cubic meter (ug/m^3).  This simplifies the process of comparing measured data to target concentrations, which are typically presented in ug/m^3.  Note that converting between some units of vapor concentration can be more involved than converting between standard units of soil and groundwater concentrations.  For a conversion table, see the last page of the Vapor Intrusion Pathway A Practical Guide (ITRC 2007) document.

Laboratory Reporting Limits

It is important to consult with the laboratory when planning a soil gas, sub-slab, or indoor air sampling event to ensure that the reporting limits (i.e., Practical Quantitation Limits, PQLs) for constituents of concern will be low enough to measure concentrations of interest.  For example, if indoor air sampling is being conducted for a constituent of concern with a target indoor air concentration of 10 ug/m^3, the reporting limit for the constituent must not exceed 10 ug/m^3.

Use of Screening Levels

Screening levels can be useful tools for evaluating the potential for vapor intrusion, but they should be used in context with the conceptual site model.  For example, the use of groundwater screening levels with groundwater data alone would not be adequate to evaluate vapor intrusion potential at a site that also has a release of volatile compounds to soil, because the contribution of vapor from the soil source must also be taken into account.  Additionally, site conditions may indicate the potential for unattenuated transport of vapors, rendering the use of subsurface screening levels inappropriate.  Such conditions include (USEPA 2012g):

  • Very shallow groundwater sources (for example, depths to water less than 5 ft below foundation level)
  • Shallow soil contamination vapor sources (for example, sampled at levels within a few feet of the base of the foundation)
  • Buildings with significant openings to the subsurface (for example, sumps, unlined crawlspaces, earthen floors) or significant preferential pathways, either naturally-occurring or anthropogenic (not including typical utility perforations present in most buildings)

Chemical Parameters

Toxicity values and other chemical parameters needed for calculating screening levels and running the Johnson and Ettinger Model should generally be taken from the most recent version of the USEPA Regional Screening Level (RSL) Tables.  However, if there has been an update to toxicity values by the primary source (e.g., IRIS), these updated values should be used even if they are not yet reflected in the RSL Tables.


Interstate Technology and Regulatory Council (ITRC). 2007. Vapor Intrusion Pathway: A Practical Guideline. VI-1. Washington, D.C.: Interstate Technology & Regulatory Council, Vapor Intrusion Team.

USEPA. 2008a. Brownfields Technology Primer: Vapor Intrusion Considerations for Redevelopment. Solid Waste and Emergency Response (5203P). March. EPA 542-R-08-001.

USEPA. 2008b. Engineering Issue: Indoor Air Vapor Intrusion Mitigation Approaches. October.

USEPA. 2011a. Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990-2005): A Compilation of Statistics for Assessing Vapor Intrusion. EPA 30-R-10-001. June.

USEPA. 2011b. Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion. September.

USEPA. 2012a. Conceptual Model Scenarios for the Vapor Intrusion Pathway. EPA 530-R-10-003. February.

USEPA. 2012b. EPA’s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings. EPA 530-R-10-002. March.

USEPA. 2012c. Johnson and Ettinger (1991) Model for Subsurface Vapor Intrusion into Buildings.

USEPA. 2012d. Regional Screening Level Tables.

USEPA. 2012f. Vapor Intrusion.

USEPA. 2012g. Download this pdf file. Vapor Intrusion Screening Level Calculator: User’s Guide . March.