Vapor Intrusion: It Isn't Going Away

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VAPOR INTRUSION: IT ISN’T GOING AWAY

Vapor intrusion is the migration of volatile chemicals from subsurface releases into workplaces and homes. While we have known about vapor intrusion since the 1980s, the U.S. Environmental Protection Agency (USEPA) claims that the number of sites nationwide where vapor intrusion may pose a “significant risk” has grown from 374,000 in 2004 to 439,000 in 2007.[1] The locations affected are as variable as the list is long and includes dry cleaners, gas stations and a variety of manufacturing facilities as well as private residences. Likewise, the volatile chemicals found at these sites can vary ranging from constituents of gasoline (e.g., benzene, toluene and tetra ethyl lead [TEL]) to chlorinated solvents, such as perchloroethylene (PCE) and trichloroethylene (TCE).

REGULATORY REQUIREMENTS VARY

To complicate matters, the level of regulatory involvement can vary from state to state. While only 27 out of 50 states have some form of vapor intrusion guidance, almost all of the regulators (96%) contacted during a 2005 Interstate Technology and Regulatory Council survey indicated that vapor intrusion was a concern and the majority of these regulators were actively addressing the issue.

In addition, several of the states that have been actively regulating vapor intrusion for some time are now expanding the scope of their regulation. For example, the New York Department of Environmental Conservation (NYDEC) has spent the last few years re-testing or preparing to re-test hundreds of homes and businesses statewide for vapor intrusion. Many of the sites were previously judged by NYDEC to be “clean” following site remediation. However, the discovery of hazardous vapors from decades-old chemical releases at some of these “cleaned and closed” sites has spurred NYDEC to conduct a new round of site testing.[2]

WHAT IS THE RISK?

The likelihood that a site might be at risk for vapor intrusion depends on a number of factors. The most important is the presence of volatile chemicals in the soil or shallow groundwater beneath the site. But other factors, such as the age and construction style of buildings, the building’s ventilation system, the location of utility lines, and the soil type and moisture content can have a significant impact on whether or not a particular building will have active vapor intrusion and whether the resulting vapor levels are high enough to pose a hazard to building users. For example, newer buildings often have vapor barriers incorporated into their foundations, which can prevent vapors from entering the building. By contrast, coarse-grained soils may allow for more rapid vapor migration, while fine-grained soils with higher moisture contents can inhibit vapor transport. A graphical representation of some of the factors affecting vapor intrusion is shown below:

WHAT SHOULD YOU DO?

As a general rule, one should not rush to collect samples of the air inside buildings on a site that is suspected of having a potential vapor intrusion risk. Any detection of hazardous chemicals in indoor air raises an immediate “red flag” that may or may not be associated with actual subsurface contamination. Studies have shown that high levels of indoor air contaminants can also be due to products used by the building occupant, such as spray products, adhesives, dry cleaning fluids, and paint.

A more prudent approach is to determine if a subsurface release is actually present and assess whether the release, if present, may create an unacceptable indoor air quality condition. Several steps that should be considered prior to doing indoor air sampling include:

	Reviewing available soil and groundwater data;
	Conducting a soil-gas survey;
	Collecting sub-slab samples from beneath the building; and
	Using an USEPA-approved model to assess the vapor intrusion risk.

One should also remember that, while preventing vapor intrusion can be relatively simple and cheap (i.e., barriers and/or ventilation systems can be installed), cleanup costs associated with removing subsurface contamination can be high as can the cost of third party claims filed by affected building occupants. The cost of third party claims often includes claims for perceived stigma damages, which can also be quite high.

If you would like assistance in determining if any of your sites might have a vapor intrusion problem, please contact Michael Marsden at (925) 403-6200.

[1] Nationwide site totals obtained from articles by Dong, T., Public Works, October 2004 and Brodsky, M., Risk and Insurance, May 2007.

[2] NYDEC re-testing program is described in an article by Esola, L., Business Insurance, November 2006.