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Environmental Health Investigations Branch

What is vapor Intrusion?

All soils contain numerous tiny air pockets (soil gas), like the air spaces in a sponge. If a volatile organic compound is present in the soil or groundwater, it evaporates and becomes part of the soil gas. Examples for these volatile compounds are gasoline, dry cleaning solvents like tetrachloroethylene or "PCE", industrial solvents like trichloroethylene or "TCE", or paint thinners like acetone.

Vapor intrusion occurs when soil gas enters a building through cracks in the slab, foundation, basement floor, sewer lines, or other openings. The amount of soil gas that moves into a building depends on the soil type and wetness of the soil, the air conditioning and heating settings in the building, the time residents keep windows open, the type and condition of the floor (cracks in the concrete, holes for utilities), and other factors. Once inside the building, the solvent vapors are part of the indoor air and we breathe them in.

VaporIntrusion at a home


Click below for a podcast from Dr. Kelly Pennell, a leading expert in vapor intrusion research, to learn how researchers are working to better characterize and predict vapor intrusion so that they can help communities understand what it may mean for their health.

Podcast: Vapor Intrusion and Your Health, National Institute of Environmental Health Sciences


How do volatile compounds get into the soil or groundwater? 

  • These compounds leaked from underground storage tanks, pipes, storage containers, waste materials, or the sewer system, or they were spilled on the ground. Once in the soil or groundwater, they can evaporate into the soil gas.

​What happens to the soil gas?

  • Soil gas can move through the soil and through cracks and openings in foundation slabs, crawl spaces and basements, entering the indoor air of homes. This is called "vapor intrusion."

 You can find a Factsheet with an overview of Vapor Intrusion here (in English and Spanish):

Vapor Intrusion Video

  • This two minute video from the Wisconsin Department of Natural Resources gives a good overview of the causes, how soil gas spreads underground, indoor air testing, and what can be done about Vapor Intrusion.



How can Vapor Intrusion affect us?

​​It is important to breathe clean indoor air because we spend more than 90% of our time indoors. Many factors determine how good our indoor air is: construction materials of the home, cleaning products we use and store, our lifestyle (smoking, cooking), the type of heating and air conditioning, and how often we open the windows. Sometimes chemical vapors can enter the indoor air (vapor intrusion), and sometimes naturally occurring vapors can enter the home this way (radon, methane).

Vapor intrusion of homes or buildings can become a health concern for the occupants depending on many factors, such as the type of chemical that enters the home, the amount, length of exposure and the health of the residents.


Common contaminants for Vapor Intrusion and their health effects

Below are links to factsheets from the federal Agency for Toxic Substances and Disease Registry (ATSDR) that describe potential health effects from these chemicals.

Factsheet on Benzene (in English and Spanish):

 Factsheet on Tetrachloroethylene or PCE (in English and Spanish):

Factsheet on Trichloroethylene or TCE (in English and Spanish): 


How do we investigate Vapor Intrusion?

The federal Agency for Toxic Substances and Disease Registry (ATSDR) has a factsheet on "Investigating Vapor Intrusion" (in English and Spanish):


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