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The Rising Concern with Vapor Intrusion

Vapor intrusion – the presence of potentially toxic vapors in a structure that arise from contaminated groundwater or soil below (or near) a building — can lead to health problems as well as legal exposure. If you are real estate developer or residential, commercial or industrial property owner and haven’t yet dealt with vapor intrusion, chances are you will soon, particularly at properties in urban areas.  In recent years, evolution of the environmental due diligence process and requirements of savvy lenders have resulted in a greater awareness of the potential for vapor intrusion, and in some instances the need for mitigation of actual or potential vapor intrusion.

Increasingly, vapor intrusion issues are being flagged in Phase 1 Environmental Site Assessment reports, essentially during refinancing or property acquisitions.  Some States have little regulatory guidance on how to address potential vapor issues, and others have prescriptive protocols to evaluate and address vapor concerns.  Developers and builders applying for a financing from most lending institutions are now likely to encounter requirements for due diligence relating to vapor intrusion.

Vapor Intrusion: A Rising Concern

Exposure from vapors to humans is direct; if there’s vapor intrusion (VI)  in a building, the occupants only need to breathe to be affected.  However, most of the chemicals associated with vapor intrusion don’t cause immediately noticeable symptoms for occupants of the building. Instead, long-term, low-level chronic exposure of undetected vapors can cause problems ranging from nervous system ailments and mental confusion to cancer.

VI can arise from chemicals directly under the building or on the site from past industrial activities, or chemicals from another property that have migrated to the site within the groundwater flow.  Vapor can enter a structure through floor or wall cracks, unsealed construction joints in the slab, through utility lines, or floor drains, to name a few pathways.  Vapor movement can be enhanced in some buildings by the “stack effect” due to wind and temperature variations across and through the structure.

Due Diligence

The most common first step in identifying a potential VI concern is to complete a Phase I ESA, a fairly well-established process that involves looking at the history of the property, previous operations, and the types of chemicals that may have used at the site.

The Phase I ESA also includes a search for records of spills or releases that may have been documented at the site or within a prescribed radius of the site. Typical records reviewed are inventories of leaking underground storage tanks facilities, lists of reported spills, and lists of properties that have entered a State’s cleanup program due to the detection of contaminants in soil or groundwater and, more recently, contaminated soil vapor.

Chemicals of Concern

The EPA has identified some 180 chemicals that are of concern for potentially harmful vapor intrusion. These are generally volatile organic compounds, or VOCs, that are sufficiently volatile and have potential inhalation toxicity.

Many VOCs are used in industry, but many are found in common household products. For example, benzene and toluene are components of gasoline, which many of us have in our garage for use with a lawn mower. Trichloroethylene, or TCE, is a common cleaning solvent used in industry, but it’s also found in spot removers or other cleaning agents that you might use in your garage or in the laundry room. Perchloroethylene (PCE, or perc) is a dry cleaning solvent; clothes in your home that are fresh from the dry cleaner may have some residues of perc on them. EPA has documented that these chemicals are routinely found in homes and workspaces.

Sampling and Detection

If there’s reason to suspect the possibility of vapor intrusion in a building, the next phase involves collection of samples. The process typically begins with samples of environmental media to identify VOCs (soil, groundwater, soil vapor).  Currently, soil gas samples are considered the most effective in evaluating VI potential short of  sampling indoor air. However, soil vapor is notoriously variable both spatially and temporally, so the practitioner needs to consider how many samples and over what period of time.  The answer will probably vary with the age and use of the structure, the nature of the VOC source, and the sensitivity of the potential receptors.  This is where the judgement of the practitioner and the requirements of the regulators can play a large role.

Indoor air sampling is obviously the best method to determine if a VI issue exists, however even this straightforward approach has pitfalls since VOCs can vary dramatically over time based upon a variety of factors.  And, data may be skewed by ambient concentrations of household chemicals in the structure as described earlier.


If vapor intrusion is detected in a structure, there are a variety of approaches to address the problem.

In some structures, vapor can enter through a multitude of channels, and a common approach is to try and eliminate those obvious pathways before considering more disruptive techniques. Floor joints, sumps, utility conduits, floor drains, and slab penetrations are all suspect pathways that need to be considered. If sealing of entry points is unsuccessful, the professional can consider several other mitigation approaches that will be very much both site and cost dependent.


Increasingly, as the real estate industry becomes more attuned to the issue VI and states adopt guidance and regulations, vapor intrusion is becoming a concern for owners, developers, builders and lenders. Proactively managing this issue is best tackled using a methodical approach to assess source, migration and mitigation options. Braun Intertec professionals have been addressing vapor intrusion and designing vapor mitigation systems for over 25 years.

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