Differentiating Background from Vapor Intrusion


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Differentiating Background from Vapor Intrusion

Vapor Intrusion (VI) is a term applied to chemical vapors entering a building from underground contamination. The allowable indoor vapor concentrations from VI are generally far lower than OSHA levels, and often lower than vapors from indoor sources such as carpet glue or scented candles. VI assessments therefore involve sorting out which vapors are from VI and which are from indoor sources.

Under Ohio’s Voluntary Action Program (VAP), Cox-Colvin investigated a former manufacturing facility in Central Ohio that is now used for offices and warehousing. Volatile Organic Compounds (VOCs) in soil and groundwater beneath the building suggested possible VI. Cox-Colvin collected soil gas from beneath the floor, and subsequently, indoor air. Indoor air contained unacceptable levels of benzene and chlorinated compounds, but using techniques they presented at various environmental conferences, Cox-Colvin proved that two of the three VOCs in indoor air that posed elevated risk had indoor sources. Because VI from subsurface contamination was acceptable, no further remediation or vapor mitigation was needed, and the owner was spared the costs and efforts associated with future mitigation and air testing. All of the environmental concerns have now been addressed, and Cox-Colvin is addressing the site under the Ohio VAP.