Jump to main content.

Fact Sheet

February 2010

What You Should Know About Vapor Intrusion


EPA has developed this fact sheet to answer frequently asked questions about an important health issue known as vapor intrusion. Vapors and gases from contaminated groundwater and soil have the potential to seep into indoor spaces and cause health problems.

Vapor intrusion into indoor air

What is vapor intrusion?

Vapor intrusion occurs when liquid chemicals give off gases that seep into buildings through cracks in basement walls, foundations, sewer lines or other openings. Sometimes these liquid chemicals are spilled on the ground or leak from underground storage tanks. They trickle down into the soil and groundwater, and the gases they give off travel through soil particles as vapors. These vapors then move up through the soil and into nearby buildings, contaminating indoor air.

Homes in the same neighborhood, even right next door, can be affected differently by vapor intrusion. The effects can be dependent upon the condition of the home. For instance, a home with more cracks in its foundation could be more prone to vapor intrusion. Vapor intrusion is similar to the process that occurs when radon, a naturally occurring radioactive gas, enters a home through cracks in the foundation. Vapor intrusion from chemicals is uncommon, but should be considered when there is a known source of soil or groundwater contamination nearby.

What chemicals might enter my home and how would they get there?

Volatile organic compounds (VOCs) are one group of chemicals that can easily become gases or vapors which can migrate through soil and enter buildings. Well-known examples of VOCs are petroleum products, such as gasoline or diesel fuel, dry cleaning solvents and industrial de-greasers.

One of the most common ways that vapor intrusion occurs is when petroleum that has leaked from underground storage tanks at gas stations gives off vapors that enter people's homes. This occurrence is usually accompanied by a petroleum odor. Solvents from other commercial and industrial sites are not usually accompanied by an odor. In many cases, underground chemical and petroleum leaks are not discovered until contamination has had time to travel through the soil.

When the EPA investigates possible vapor intrusion, we also take into account VOCs found in household products stored in your home. Paints, paint strippers and thinners, glues, solvents, stored fuels and dry-cleaned clothing all contain VOCs. These household products are more likely to be a source of indoor air quality problems than vapor intrusion from a chemical spill.

What are the health concerns with vapor intrusion

When vapor intrusion does occur, the health risk will vary based on the type of chemicals, the levels of chemicals found, the length of exposure and the health of the exposed individuals. When chemicals build up in indoor air at high levels, some people may experience health effects such as eye and respiratory irritation, headaches and/or nausea. These symptoms are temporary and should go away when the person moves to fresh air. Usually, health officials are more concerned about low-level chemical exposures over many years. Long-term exposure to some chemicals may raise a person's lifetime risk of developing cancer or other chronic diseases.

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 the risk posed by radon or by household chemicals used by the residents. Even though the risk is quite low, the EPA and many health agencies consider these risks to be unnecessary and avoidable.

What should I do if vapor intrusion is a concern in my home?

If you live near a cleanup site where petroleum or other VOCs have contaminated soil or groundwater, you should ask the officials overseeing the cleanup if the potential for vapor intrusion is being investigated. You may be contacted by the cleanup team working on the site. They may provide information about the project or request assistance from you. Your cooperation and consent may be requested, so that testing can be done on your property.

How is vapor intrusion discovered?

In most cases, the potential for vapor intrusion can be ruled out by collecting soil gas or groundwater samples near the contamination site. If contamination can be ruled out near the site, then it may be unnecessary to look any farther out. If contamination is found in soil gas near the homes, the next step is to take vapor samples from the soil under the home's foundation; these are called sub-slab samples. EPA does not generally recommend indoor air sampling before sub-slab sampling. Sub-slab samples are more reliable indicators of potential vapor intrusion than indoor air samples and are not affected by other indoor chemical sources. If no soil vapors are detected outside the home, additional indoor air sampling may not be necessary as long as the site is being cleaned up effectively. If sub-slab vapors are detected outside the home above EPA's projected health concern levels, additional indoor air sampling should be done to determine if those vapors are present inside and at what levels. Indoor air quality changes a lot from day to day. Therefore, sampling one day may not show a problem, and the next day it will.  A variety of VOC sources are present in many homes and in outside air, which replaces indoor air constantly. Therefore, testing will not necessarily confirm that the VOCs in the indoor air are entering the home from outside underground sources.

What happens if a problem is found?

The most common solution is to install systems often used to reduce naturally occurring radon that seeps into homes in some parts of the country. These systems, called radon mitigation systems, remove soil vapors from below basements or foundations before they enter homes. Vapors are vented outside of the homes where they become dispersed and harmless. These systems use minimal electricity and do not noticeably affect heating and cooling efficiency. They also prevent radon from entering homes - an added health benefit in radon prone areas. Once the source of the vapors is eliminated, the systems should no longer be needed. In homes with radon problems, these systems should remain in place permanently.

What can I do to improve my indoor air quality?

Consider these tips to improve indoor air quality in your home:

For more information:

For health-related questions regarding vapor intrusion, contact your local health department or the Agency for Toxic Substances and Disease Registry at 1-888-422-8737 or visit their Website at www.atsdr.cdc.gov.

For more information on indoor air quality, visit EPA's Website at www.epa.gov/iaq or call the Indoor Air Quality Information hotline at 1-800-438-4318.

For more information about ongoing site cleanup actions or vapor intrusion investigations in EPA Region 7 (Iowa, Kansas, Missouri, Nebraska and associated tribal nations), contact:

Mary Peterson, Superfund Division
Telephone:  913-551-7882
E-mail: peterson.mary@epa.gov


Dan Nicoski, Environmental Services Div.
Telephone:  913-551-7230
E-mail: nicoski.dan@epa.gov

Local Navigation

Jump to main content.