by Wesley Robb
Vapor intrusion occurs when there is a migration of chemicals containing vapor from a subsurface source such as soil, groundwater, or soil vapor into an overlying building (Figure 1). As a result of past activities, some areas are more prone to the risk of vapor intrusion for its surrounding structures. For example, erstwhile sites of dry cleaners or filling stations could possibly place an area at risk as toxic chemicals like petroleum hydrocarbons and chlorinated solvents were used in these locations. (For more information on vapor intrusion, visit www.constructionspecifier.com/the-growing-concern-with-vapor-intrusion.)
If poisonous vapor chemicals are present in the soil, groundwater, and/or soil vapor, they may migrate into a nearby structure. This may adversely affect a building’s indoor air quality (IAQ), leading to potential health problems for building occupants. (Chemicals typically encountered in a vapor intrusion scenario can have varied health effects—from lung cancer, decreased kidney function, damage, and cancer, heart failure, and ischemia [decreased oxygen supply] to increased sensitivity to allergens, immune system impairment or failure, auto-immune effects, skin irritation, rash, discoloration, dermatitis, liver damage or tumors, steatosis, and death of liver cells.) Addressing vapor intrusion sites is an outgrowth of years of legal precedence, which flows from the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), or ‘Superfund,’ and the Resource Conservation and Recovery Act (RCRA). These laws developed the framework for managing and remediating hazardous waste sites, and form the framework for legal precedence in vapor intrusion litigation.
There have been documented cases of lawsuits brought upon building owners, where health problems caused by vapor intrusion were cited as the reason. In 2010, a summary judgment was granted against property owners who, as the federal district court in Nevada determined, knowingly developed housing over a groundwater plume contaminated by dry-cleaning chemicals. (In the Voggenthaller v. Maryland Square case, the federal district court in Nevada cited homeowners were endangered by the contaminated groundwater and chemical vapors emanating from the groundwater plume.)
As more studies are conducted by U.S. Environmental Protection Agency (EPA) and similar agencies, awareness is growing about the threat of vapor intrusion. EPA has paid particularly close attention to trichloroethylene (TCE) because findings have revealed this industrial solvent poses potential human health hazards, including cancer. (Of notable concern is the possibility fetal heart defects may result if pregnant women are exposed to TCE in their earliest stages of gestation.)
More architects are specifying chemical vapor barriers when designing a new structure in locations where vapor intrusion may be a concern. On receiving these specifications, contractors are able to hire certified installers to put in a chemical vapor barrier system during construction even before the foundation is laid. This practice helps mitigate the risk vapor intrusion poses.
Chemical vapor barriers are not to be confused with standard moisture barriers (often simply referred to as ‘vapor barriers’). The latter is designed to keep moisture out of a building in an attempt to reduce the potential for mold, which can also be a health risk, and water damage. Chemical vapor barriers, on the other hand, are designed to not degrade or allow penetration of vapor-phase chemicals. The fact moisture barriers are often described as ‘vapor barriers’ in the industry can lead to confusion.