In April 2013, the Environmental Protection Agency (EPA), Office of Solid Waste and Emergency Response (OSWER) published for comment two draft vapor intrusion guidance documents: (1) a revised update addressing general vapor intrusion (VI Guidance) and (2) a new document addressing vapor intrusion from petroleum hydrocarbons. The agency has recently extended the public comment period until June 24, 2013.

EPA defines vapor intrusion as the migration of vapors emitted from volatile chemicals present in contaminated groundwater or soil into an overlying building. The Agency is concerned that vapors may accumulate in overlying buildings at levels posing near-term safety hazards, acute and/or chronic health effects, or aesthetic problems.


The VI Guidance, if finalized in its current form, will address the investigation and remediation of the full range of vapor-forming chemicals and vapor intrusion risks present at sites remediated under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)1 , the Resource Conservation and Recovery Act (RCRA)2 , and federal brownfield redevelopment programs. In particular, EPA has identified vapor intrusion as a concern at former industrial sites, gas stations, and dry cleaners where perchloroethylene (PCE), trichloroethylene (TCE), and other chlorinated solvents were widely used.

This is not EPA’s first effort to address vapor intrusion. In 2002, the Agency released draft guidance that has served as the basis for conducting vapor intrusion exposure assessments and governed mitigation efforts; however, it was never finalized. In December 2009, the EPA’s Office of the Inspector General recommended that the 2002 draft be updated and finalized. In response to this recommendation, EPA issued the revised draft VI Guidance, which expands upon and supersedes the 2002 version, as well as any EPA regional office-specific guidance.

The VI Guidance: (i) provides methods to account for “background” contributions to indoor air concentrations; (ii) develops a risk management framework for planning and conducting evaluations; (iii) updates screening levels and attenuation factors; (iv) emphasizes the use of multiple line of evidence to evaluate vapor intrusion risks (e.g., use of biodegradability and geologic and hydrologic evidence to support cleanup decisions); (v) implements new community involvement and institutional control requirements; and (vi) requires the use of vapor intrusion exposure mitigation controls and systems.


The 2002 draft guidance did not specifically cover assessment and mitigation of petroleum vapor intrusion. Thus, in conjunction with the VI Guidance, EPA also issued a draft guidance document regarding the assessment and mitigation of vapor intrusion from petroleum hydrocarbons (“Petroleum VI Guidance”).

The Petroleum VI Guidance focuses on the typical constituents of petroleum products such as benzene, toluene, ethylbenzene, and xylene, as well as gasoline additives. However, the draft is limited to petroleum releases from underground storage tanks (USTs), such as releases at the typical corner gas station.

Further, the Petroleum VI Guidance explains how to: (i) assess immediate threats to safety; (ii) conduct a site characterization and prepare a conceptual site model; (iii) identify critical transport pathways; and (iv) mitigate petroleum vapor intrusion. The Petroleum VI Guidance also introduces the concept of inclusion zones that identify the distance between contamination and overlying structures for which biodegradation is sufficient to eliminate the vapor intrusion threat.


  • Interplay of the VI Guidance with State Vapor Intrusion Regulations and Guidance

Due to EPA’s delay in issuing final VI Guidance, many states have stepped in to fill the void, creating a patchwork of guidance and regulations.

At least thirty-seven states have issued some form of vapor intrusion regulations or guidance, including many states in the northeast (e.g., NY, NJ, CT, MA, NH), and on the west coast (e.g., CA, OR, WA, AK). The result is a myriad of vapor intrusion site assessment protocols, including screening-levels that differ across states by as much as a factor of ten for the same chemical and exposure.

It is unclear how the VI Guidance will affect the existing state programs. States with existing regulations and published guidance may realign with the VI Guidance or may choose to impose their own stricter standards. Moreover, states without existing protocols may decide to adopt the VI Guidance in whole or in part.

  • Impact of the VI Guidance on OSHA Permissible Exposure Levels for Worker Safety

The Occupational Safety and Health Administration (OSHA) has developed a separate set of standards for indoor air concentrations for worker exposure, known as Permissible Exposure Levels (PELs) (29 C.F.R. Part 19, subpart Z). It is unclear how the VI Guidance will impact these standards, as well as other workplace safety requirements. This uncertainty is of concern given that the VI Guidance expands the assessment and mitigation of vapor intrusion to nonresidential buildings, such as hospitals, schools, and hotels with a high degree of occupancy, as well as where workers are present.

  • Use of the VI Guidance to Address Vapor Intrusion Issues at Closed Sites

Significantly, vapor intrusion may become an issue at sites that have been remediated under CERCLA, RCRA, or brownfield redevelopment programs. Before the 2002 VI Guidance was issued, EPA lacked a consistent programmatic approach for evaluation of the vapor intrusion pathway. Therefore, at older sites it may not have been adequately addressed in the risk assessment and subsequent management decisions. More recently, EPA has adopted a policy of including a vapor intrusion assessment at remediated CERCLA sites during the scheduled Five Year Review, thus potentially leading to “reopening” remedy considerations at such sites to address risks identified due to vapor intrusion.

“Reopeners” are of particular concern at state-lead sites where new vapor intrusion screening levels are below the risk-based remediation goals. Accordingly, even if a certificate of completion or a No Further Action letter (or its equivalent) was issued previously, the state agency still could reopen a site to address vapor concerns.

  • Use of the VI Guidance in Environmental Due Diligence

ASTM’s revised environmental due diligence standards will be released in late 2013, and are expected to include a requirement to consider vapor intrusion. Thus, the VI Guidance will impact the manner in which environmental due diligence is conducted in real estate and merger/acquisition transactions.

For example, the presence of vapor intrusion and its potential pathways will be considered in a Phase I Environmental Site Assessment (ESA). As a result, more costly and time consuming evaluations of off-site sources and agency files may be required.

Moreover, the risk of “reopeners” at sites where vapor intrusion was not previously addressed or where stricter screening levels now apply will add a new level of risk when purchasing or acquiring property.


The VI Guidance may significantly alter the contamination assessment and mitigation landscape. EPA’s emphasis on using multiple lines of evidence to address vapor intrusion underscores the complex nature of the analysis. Vapor intrusion assessment is further confounded by screening levels that are in the range of typical indoor air background concentrations. Entities that may be impacted by the new VI Guidance should consider filing comments by the June 24, 2013 deadline.

Before engaging in any activities at a site where vapor intrusion may be an issue, consideration should be given to consulting with experienced environmental practitioners to better understand the potential liabilities and ways to mitigate the risks posed by state and U.S. programs. Information also can be found on OSWER’s dedicated Vapor Intrusion website.

Co-authored by James F. Lape, Peter W. Zimmermann, David Livermore, R.G., L.H.G, from Integral Consulting Inc.