Development Strategies to Manage Vapor Intrusion Risks

Due to potential health and safety risks that vapor intrusion may cause residential occupants, considerable measures must be taken to abate and clean up these vapors

By Andy Bajorat

Vapor intrusion continues to be a hot issue with state Environmental Protection Agencies. Due to potential health and safety risks that vapor intrusion may cause residential occupants, considerable measures must be taken to abate and clean up these vapors. To help manage these risks, focus on identifying the problem in the due diligence process, addressing the problem through abatement and re-allocating liability through risk mitigation alternatives. These three steps will help manage the risk and associated costs associated with dealing with vapor intrusion problems.

Due Diligence

Vapor intrusion occurs when gasoline, solvents, mercury or other volatile constituents in soil or groundwater seep upward from the ground into overlying residences through cracks and joints in foundations. These constituents, commonly referred to as volatile organic compounds (VOCs), can be present in the ground at properties that were formerly used for gas stations, dry cleaners and other industrial purposes. So, knowing your site’s history is critical to knowing if vapor intrusion may be present at your residential redevelopment.

You can identify sites where vapor intrusion is likely to occur through a few basic tasks when evaluating an acquisition of a property. Typically, that due diligence comes in the form of performing a Phase I Environmental Site Assessment (Phase I ESA) to identify if a property has been contaminated by its past or current uses. Another non-invasive evaluation frequently performed prior to acquiring a site is a vapor encroachment screen, which is an ASTM process to determine if volatile constituents are likely to be present in the ground at your site due to releases from neighboring off-site sources.

If conditions appear favorable for vapor intrusion at your development, you’ll want to test the site’s soil, groundwater and/or soil gas (air found underground) and compare VOC levels to applicable State or Federal guidelines in order to know if there’s a problem. Sites where VOCs are found above regulatory criteria typically require abatement.

If vapor abatement is required, most regulatory agencies allow you to implement various options that involve installation of engineered systems (Building Control Technologies [BCT]), the use of institutional controls (e.g. land use restrictions), or both. Common BCTs include passive and active sub-slab depressurization (similar to a radon system), sub-membrane depressurization, and physical barriers constructed of a chemical-resistant material. The appropriate BCT for your site depends on various factors, such as the intended use of the building; the nature of the VOCs; the size of the project; and whether the BCT is installed concurrent with new construction or requires retro-fitting existing facilities. Vapors from BCTs are typically discharged into the atmosphere without treatment above the building roof line. Design or pilot testing may be required for active BCTs prior to installation, especially at sites with more complex contamination issues, sites that cover a large area, and industrial facilities with variable heating, ventilation, and cooling needs.

Institutional controls may be required for a given BCT, and are typically a legally binding instrument recorded on the property deed. Potential examples include a restriction on the use of the property; a requirement to operate and maintain barriers and equipment; and specific requirements for or restrictions on building modifications. Institutional controls may be short-term (e.g. until cleanup objectives are achieved), or long-term (e.g. if the source of VOCs will remain for the foreseeable future). You should research your state’s regulations for specific requirements.

Risk Mitigation Alternatives
In addition to installation of systems that can shield occupants from underlying vapors, developers can reallocate risk through different contractual mechanisms. For instance, you can seek contractual indemnities from the property owner selling the contaminated property to limit exposure to lawsuits and to assign the responsible party that may be required to notify environmental regulatory agencies if vapor conditions are occurring. Cost allocation alternatives can also be negotiated during property transactions, such as the establishment of escrow agreements with the seller to pay for any required vapor intrusion mitigation systems that might be required.

Andy Bajorat, CHMM, has worked in the environmental industry for more than 20 years. He currently serves as Chief Operating Officer and Principal at BBJ Group, an environmental consultancy firm. He may be reached at

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