Vapor Intrusion

Vapors from past chemical spills can impact indoor air quality

Soil gases can contain harmful vapors from volatile organic compounds (VOCs) that. These vapors seep indoors through floors and pipes and produce a health risk to those inside the buildings. Volatile Organic Compounds (VOC) are a group of chemicals that easily become gases, such as petroleum products like gasoline or diesel fuel and dry cleaning and industrial solvents.

Homes in the same neighborhood and right next to each other can be affected differently by vapor intrusion. Vapor intrusion is similar to how radon can enter a home through cracks in the foundation. Vapor intrusion is uncommon, but should be considered whenever there is a known source of soil or groundwater contamination nearby.


Vapor Intrusion 101


Vapor intrusion can make people sick

The health effects from chemical exposures vary based on the individual exposed and the chemical involved.  When chemicals build up in indoor air (at levels high enough to cause a strong petroleum odor, for example), some people will experience eye and respiratory irritation, headache, and/or nausea. These symptoms are temporary and should go away when the person is moved to fresh air.  Usually, health officials are most concerned about low level chemical exposures over many years, as this may raise a person’s lifetime risk for developing cancer.

The likelihood of indoor air contamination by vapor intrusion is low at most cleanup sites. When vapor intrusion does occur, the health risk will often be lower than that posed by radon or by chemicals owned and used by the resident. Even though the risk is quite low, the Wisconsin Department of Health Services (DHS) considers these risks to be unnecessary and avoidable.

Expect contamination to be inspected

The most common vapor intrusion cases involve petroleum spilled or leaked from underground storage tanks at gas stations. These cases are usually accompanied by a petroleum odor. Solvents from other commercial sites and industrial sites are usually not accompanied by an odor. In many cases, chemical and petroleum releases are not immediately discovered. By the time they are discovered, the contamination has had time to migrate through the soil.

If you live near a site with VOC contamination you should expect that the potential for vapor intrusion is also being investigated. You may be contacted by the cleanup site owner or others working on the cleanup with information about the project. Your cooperation and consent would be requested before any testing/sampling would be done on your property. You may ask the person contacting you any questions about the work being done.

For an online DNR database of sites with environmental contamination, follow the "BRRTS on the Web" button from the Remediation and Redevelopment page.

Samples are taken from around the home

In most cases, the potential for vapor intrusion can be ruled out by collecting soil gas or groundwater samples near the contamination site. In some cases, sampling closer to your property and/or home may be necessary. DHS and DNR do not usually recommend indoor air sampling for vapor intrusion since indoor air quality changes day to day. Instead, soil vapor samples are taken from areas outside of the home to see if vapors are near the home.

Samples may also be taken from beneath the home’s foundation, called sub-slab sampling, to see if vapors have reached the home. Sub-slab samples are more reliable than indoor air samples and are not as affected by other indoor chemical sources. If no odors are present at a petroleum cleanup site, additional testing may not be necessary as long as the site is being cleaned up effectively.

Install a mitigation system to reduce exposure

If vapor intrusion is having an effect on the air in your home, the most common solution is to install a radon mitigation system that prevents gases in the soil from entering the home. This mitigation system also prevents radon from entering the home, an added health benefit.

Usually, the party responsible for cleaning up the contamination is also responsible for paying for the installation of this system. Once the contamination is cleaned up, the system should no longer be needed. In homes with radon problems, DHS suggests that these systems remain in place permanently.

Resources for Environmental Professionals

Household products can be a source of VOCs

Paints, paint strippers and thinners, cigarette smoke, aerosol sprays, moth balls, air fresheners, new carpeting or furniture, hobby supplies (glues and solvents), stored fuels, and dry-cleaned clothing all contain VOCs. For this reason, household products are more likely to be a source of indoor air quality problems at your home than vapor intrusion from a contamination site.

Tips to improve air quality:

  • Do not buy more chemicals than you need at a time.
  • Store unused chemicals in appropriate containers in a well-ventilated location.
  • If you smell a chemical odor that does not seem to be from an indoor source, contact your local health department.
    • For very strong odors, your local fire department can determine if there is a fire hazard.
  • Don’t make your home too air tight - fresh air will help prevent both build up of chemicals in the air and mold growth.
  • Fix all leaks promptly and control moisture that encourage mold growth.
  • Have all major appliances and fireplaces checked annually by a professional.
  • Test your home for radon!



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Last Revised: November 6, 2017