Vapor Intrusion and Vapor Pathway Assessment

Vapor intrusion into occupied structures is a concern that was first recognized as the entrance of sewer gas into structures. Vapor intrusion was also clearly demonstrated by the explosion of homes constructed on former landfills as a result of the build up of methane gas. More recently, gasoline releases from underground storage tanks have been identified as the cause of exposure to hazardous and explosive vapors in nearby residential structures.

Vapor intrusion into occupied buildings requires relatively high contaminant concentrations in close proximity to the building and, therefore, is not a common exposure scenario. However, the risk associated with this exposure route is relatively high. In the event that free product is migrating toward occupied structures due to a large release of a very volatile compound, such as gasoline, or due to the presence of a preferential pathway, there is great potential liability for the responsible parties.

Routes of Vapor Exposure

Vapors are drawn into structures as a result of the presence of a high concentration of vapors in the subsurface in close proximity to the structure and the pressure gradient between the atmospheric pressure in the subsurface and the negative pressure in the structure as a result of heating systems and stack effects. The most common route by which high vapor concentrations are present near the building foundations is a preferential pathway. Preferential pathways are routes by which vapors can move much more readily than in the remainder of the subsurface. Such preferential pathways include sewer lines, the coarse backfill surrounding underground utilities, and storm water systems.

Assessment of the routes for vapor exposure is included in the exposure pathway identification portion of a risk assessment. Assessment of the presence and completeness of this exposure pathway is critical for directing risk-based corrective actions and ultimately obtaining regulatory closure for a release.

Vapor Intrusion and Vapor Exposure Assessment Services

GeoServices, Ltd. provides vapor exposure assessment services to establish attainable risk-based site-specific cleanup goals and in support of litigation. Vapor exposure is frequently cited by plaintiffs as a source of health risk as well as monetary damages. As noted above, vapor intrusion is not a common pathway making it critical that highly qualified professionals are utilized to assess the presence, completeness, and magnitude of the risk for exposure through vapor intrusion. Whether your concerns are a cost-effective site remediation where vapors may be present or the assessment of vapor intrusion damage claims, GeoServices has the experience and expertise to provide a professional, scientific and supportable assessment.

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Storage Tanks

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