Vapor Intrusion

Vapor intrusion is a way in which chemicals in soil or groundwater can get into indoor air (see figure at right). These chemicals may be released to the soil and groundwater from various sources including chemicals spilled on the ground at a factory or leaked from an underground storage tank. These chemicals can seep down into the soil and groundwater. Some chemicals also can travel through soil as vapors. These vapors may then move up through the soil and into nearby buildings through cracks in the foundation, contaminating indoor air. Homes in the same neighborhood and even those next to each other can be affected differently by vapor intrusion. Vapor intrusion is uncommon, but should be considered whenever there is a known source of soil or groundwater contamination nearby.

Volatile organic compounds (VOCs) are one group of chemicals that easily become gases and can move through the soil and enter buildings. Some examples of VOCs are petroleum products such as gasoline, chemicals for dry cleaning and industrial products.

Some VOCs also are found in products that may be in your home. 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 and are more likely to be a source of VOCs in your home than vapor intrusion.

Vapor intrusion cases sometimes involve VOCs that have leaked from underground storage tanks. Leaks from underground gasoline tanks are usually accompanied by the smell of fuel.

The health effects from chemical exposures vary based on the individual exposed and the chemical involved. When chemicals build up in indoor air (levels high enough to cause an odor), some people may experience eye and respiratory irritation, headache or nausea. These symptoms are temporary and should go away when the person is moved to fresh air. Some VOCs have been associated with cancer. Low-level exposures to these VOCs, over many years, may raise a person’s lifetime risk for developing cancer.

If you live near a site with VOC contamination, such as a refinery, gas station or dry cleaner where VOCs have contaminated soil or groundwater, the potential for vapor intrusion may be investigated. You may be contacted by the site owner or others working on the cleanup with information about the project. Your cooperation and consent would be requested before any testing or sampling would be done on your property. You may ask the person contacting you any questions about the work being done.

In most cases, the potential for vapor intrusion can be ruled out by collecting soil gas or groundwater samples near the site. In some cases, sampling closer to your home may be necessary. Since a variety of VOC sources are present in most homes, testing will not necessarily confirm that VOCs in the indoor air are from VOC contamination in soils nearby. Instead, soil vapor samples may be taken from areas outside of the home to see if vapors are near the home. Samples also may be taken from beneath the foundation of the house (called sub-slab samples) to see if vapors have reached the home. Sub-slab samples can be compared to indoor air samples to determine if VOCs in the home are from vapor intrusion.

If vapor intrusion is affecting the air in your home, a common solution is to install a sub-slab mitigation system. This prevents gases in the soil from entering the home. A low amount of suction is applied below the foundation of the house and the vapors are vented to the outside. The system uses minimal electricity and should not noticeably affect heating and cooling efficiency. Sometimes, the party responsible for cleaning up the contamination also is responsible for paying for the installation of this system. Once the contamination is cleaned up, the system should no longer be needed.

Illinois Department of Public Health 
Division of Environmental Health 
525 West Jefferson Street 
Springfield , Illinois 62761 
217-782-5830
TTY (hearing impaired use only) 800-547-0466

This fact sheet was supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund through a cooperative agreement with the Agency for Toxic Substances and Disease Registry, Public Health Services, U.S. Department of Health and Human Services.
Updated February 2009