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What is vapor intrusion?
Vapor intrusion is a way that chemicals in soil or groundwater can get
into indoor air. (see figure at right) Sometimes, chemicals are spilled on
the ground at a factory or leak from an underground storage tank.
These chemicals can seep down into the soil and groundwater. Some
chemicals can also travel through soil as vapors. These vapors may
then move up through the soil and into nearby buildings, contaminating
indoor air. 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, a naturally occurring radioactive gas, 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.
What chemicals might be entering my home, and where would they come
VOCs (volatile organic compounds) are one group of chemicals that
easily become gases which can migrate through the soil and enter
buildings. Some examples of VOCs are petroleum products such as
gasoline or diesel fuel, and solvents for dry cleaning and industrial
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.
Some of these same solvents are also found in household products which
may be stored 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. 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. In some extreme cases, health symptoms can be experienced
as a result of exposure to chemicals stored in the home.
What are the health concerns with vapor intrusion?
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 personís 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.
What should I expect if vapor intrusion is a concern near my
If you live near a site with VOC contamination, such as a gas
station or dry cleaner where petroleum or chemicals have contaminated soil
or groundwater, 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, or you can
contact the DNR cleanup project manager, or a DHS employee.
Telephone numbers and internet addresses for DHS and DNR are provided
How is vapor intrusion investigated?
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. Indoor air quality changes a lot from
day to day. Therefore, sampling one day may not show a problem even
though sampling a day later might show contamination. 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 are taken from areas
outside of the home to see if vapors are near the home. Samples may
also be taken from beneath the homeís foundation (called sub-slab
samples), 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.
What happens if a problem is found?
If vapor intrusion is having an effect on the air in your home, the
most common solution is to install a radon mitigation system.
This prevents gases in the soil from entering the home. A low amount
of suction is applied below the foundation and the vapors are vented to
the outside. The system uses minimal electricity and should not
noticeably affect heating and cooling efficiency. 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.
What else can I do to improve my air quality?
There are other sources of indoor air problems. Consider
these tips to improve air quality:
- Do not buy more chemicals than you need at a time. Be aware of
what products contain VOCs.
- Store unused chemicals in appropriate containers in a
- 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
- Donít 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, as well as other moisture problems that
encourage mold growth.
- Make sure all major appliances and fireplaces are in good
condition. Have them checked annually by a professional.
- TEST YOUR HOME FOR
For more information
For health related questions, contact your local health
department or DHS at (608) 266-1120. More information on this and
related topics is available on the DHS
website. For an on-line DNR database of sites with environmental
contamination, follow the "BRRTS on the Web" button from the
and Redevelopment page.
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September 03, 2014