What is Vapor Intrusion?
Vapor Intrusion is the migration of volatile chemicals from subsurface soil and/or groundwater into the indoor air of overlying buildings. Most Vapor Intrusion events occur when volatile organic compounds (VOCs) are released into the subsurface from underground storage tanks, dry cleaners, gasoline stations, or industrial processes such as degreasing metals. VOCs have a high vapor pressure which means they can move to a gaseous state easily. As a gas, they can migrate upward and into buildings, resulting in potential health concerns for occupants who inhale contaminant vapors. In many cases, by the time they are discovered, Volatile Organic Compounds (VOC’s) have had time to migrate through the soil and groundwater until they reach and impact buildings. Among the VOCs of greatest concern for Vapor Intrusion are chlorinated solvents and gasoline derivatives including carbon tetrachloride, tetrachloroethene (PCE), trichloroethene (TCE), methylene chloride, benzene, and methyl tert-butyl ether (MTBE). The health risks associated with compounds depends on the toxicity of the individual chemical and the concentration of that chemical in the building.