Beneath the Surface

Developments in vapor intrusion regulation and why they matter.

March 21, 2017 Photo

For over a decade, vapor intrusion has received increasing attention as an environmental and human health concern. A product of the increase in attention has been the publication of standards and guidance for the assessment and mitigation of vapor intrusion by federal and state regulators. This includes significant actions taken by the Environmental Protection Agency (EPA) to address vapor intrusion that are likely to create an increase in remediation costs at contaminated sites. They also may result in a greater number of sites being designated on the Superfund: National Priorities List (NPL).  

Given the number of properties across the country affected by historic subsurface contamination or the migration of subsurface contaminants, it is increasingly important to understand what vapor intrusion is, the actions that the EPA is taking to address vapor intrusion, and the potential for new claims that may arise as a result of those actions. 

What Is Vapor Intrusion?

Vapor intrusion (VI) is the migration of volatile chemicals from contaminated groundwater or soil into an overlying building or other occupied enclosed space. Volatile chemicals are capable of emitting vapors that may migrate through the subsurface soils and into the indoor spaces of overlying buildings through cracks and gaps in building foundations, basement floors and walls, sewer lines, or other openings. These vapors then may accumulate in buildings and, if not properly and adequately mitigated, create any number of risks to human health. VI is a concern for any building located near soil or groundwater that may be contaminated with volatile chemicals. Some of the contaminants that are commonly associated with VI include: volatile organic compounds, such as perchloroethylene and trichloroethylene; vinyl chlorides; landfill gas (methane); and petroleum products.

EPA Actions 

In recent years, the EPA has taken significant actions to more directly address VI at contaminated sites. These actions include issuance of two guidance documents aimed at promoting national consistency in the assessment and mitigation of VI and a proposal for rulemaking that would make VI a component of the Hazard Ranking System (HRS), which is used to determine whether sites are eligible for the NPL. 

In 2015, the EPA issued two final guidance documents aimed at addressing VI. First, the “Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air” is intended for use at properties being evaluated under remediation programs, including the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), Resource Conservation and Recovery Act, and brownfield sites. The guidance provides a plan for the investigation of potential for VI issues that begins with an evaluation of the site based on currently available data, followed by a more detailed investigation of the physical site conditions, including indoor air quality of existing structures. At sites, VI is determined to pose a risk. Even at sites that may have been closed for years, the guidance document calls for mitigation of the risk that may include remediation or additional remediation of the subsurface vapor source, engineered controls for existing structures, additional monitoring, and/or restrictions on land use or activities at the site. 

The second EPA guidance document, the “Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites,” is focused on the investigation and assessment of petroleum-contaminated sites where vapor intrusion by petroleum hydrocarbons may occur. The guide calls for screening criteria that are based on the distance between a petroleum-based subsurface vapor source and a building potentially impacted by that vapor source. This guidance is focused particularly on sites that have the potential for petroleum vapors but excludes many sites that do not involve underground storage tanks, such as pipelines and refineries.

In addition to the 2015 guidance documents, in December 2016, the EPA finalized a rule that makes VI a hazard to be evaluated under the HRS system for NPL sites. Prior to the finalized rule on VI, even though NPL sites might have VI issues, VI pathways alone were not enough to qualify a site for listing on the NPL. With this new rule, the EPA may directly consider VI exposure when determining if a site qualifies for the NPL, potentially creating a broader range of sites that may be listed on the NPL. With this broader range of sites comes a corresponding risk for an increase in potentially responsible parties that may be receiving notice letters or information requests pursuant to CERCLA inquiries that trigger a policy’s duty to defend.

Liability and Risk Considerations

The increase in emphasis on VI raises any number of concerns about an insured’s remedial obligations and private litigation challenges. Notably, section 121 of CERCLA, as amended by the Superfund Amendments and Reauthorization Act, requires that remedial actions at Superfund sites that result in hazardous substances, pollutants, or contaminants remaining at the site be reevaluated every five years. The purpose of this reevaluation is to determine if the site’s prior remedial actions have been and will continue to be protective of human health and the environment. The EPA guidance discussed above provides a framework for assessing VI at these sites during the five-year review process. The reevaluation of VI is required even at sites where vapor intrusion was not addressed as part of the original remedial action. 

These reviews are important because many EPA Superfund consent decrees allow for additional remedial actions where potentially harmful conditions not previously known to the EPA are discovered at the site. Thus, discovery of VI issues on reevaluation may result in the reopening of closed Superfund sites to address VI mitigation not previously considered. When a reopening action occurs, it’s likely to lead to new policyholder claims for defense and indemnity coverage for the additional assessment and remediation costs associated with the VI mitigation required at the site.

Even though the EPA’s VI guidance documents are intended for regulatory evaluations, it is highly likely that the standards set for VI assessments will be promoted as a standard of care in private tort litigation. These private actions may arise in the form of toxic torts for exposure to vapors from contaminated groundwater or soils, nuisance, or even property damage claims for diminution in value and stigma. 

Finally, VI is not just a concern for parties that may have contributed to the source of vapors at a property. It most likely will impact all landowners, developers, and parties to contaminated property transactions, who may now utilize the EPA’s guidance documents when looking to limit liability and reduce VI risks in property transactions and construction projects. 

For more information about vapor intrusion or to view source material used for portions of this article, go to

About The Authors
Multiple Contributors
Robert W. Petti

Robert W. Petti is of counsel with Segal McCambridge Singer & Mahoney. He can be reached at

Antonietta Castano

Antonietta Castano is manager, construction defect, environmental and surety claims, for Crum & Forster. She can be reached at

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