Vapor intrusion occurs when there is a migration of vapor-forming chemicals from any subsurface source into an overlying building. Recognition of soil vapor intrusion to buildings and other enclosed spaces occurred in the 1980s with concerns over radon intrusion. Subsequently, there was an increasing awareness that anthropogenic chemicals (e.g., petroleum hydrocarbons and chlorinated solvents) in soil, groundwater, and sewers and drainlines could also pose threats to indoor air quality via the vapor intrusion pathway.
- volatile organic compounds (VOCs), such as trichloroethylene and benzene.
- select semivolatile organic compounds, such as naphthalene.
- elemental mercury.
- some polychlorinated biphenyls and pesticides.
In extreme cases, the vapors may accumulate in dwellings or occupied buildings to levels that may pose:.
- near-term safety hazards (e.g., explosion)
- acute health effects
In buildings with lower concentrations of vapor-forming chemicals arising from vapor intrusion, the main concern is whether the chemicals may pose an unacceptable risk of health effects due to long-term (i.e., chronic) exposure to these lower levels.