Vapor intrusion refers to the movement of volatile chemicals from the subsurface into the indoor air of overlying buildings. The most common source is groundwater or soil contaminated with volatile organic compounds (VOCs). VOCs emit vapors that migrate into pore spaces of the soil and upward into the overlying environment.
Generally, vapors enter buildings through cracks and openings in the foundations because of a difference between interior and exterior pressures. Pressure differences occur due to many factors, including barometric fluctuations, wind load, thermal currents, and depressurization from exhaust fans and ventilation or heating systems in buildings.
Chemicals such as BTEX and TCE breakdown and produce vapors, that if accumulate to high levels, can pose shortterm safety concerns such as explosions; chemicals such as benzene and vinyl chloride are toxic when inhaled. More often, vapor concentrations are present at low levels; this can cause chronic health effects if exposure to them is long-term.
Vapor intrusion monitoring and soil vapor sampling is essential for risk assessments, especially at Brownfield re-development sites, to determine the potential exposure and risk to aboveground receptors.