Last updated Aug. 4, 2017
Vapor intrusion (VI) is a below ground source of indoor air pollution in which vapors enter people's homes or businesses through cracks or other openings in the foundation. These cracks could be from plumbing and sewer lines and electric conduits. Concentration of volatile organic compounds (chemicals that can easily become vapors or gases) may reach levels that become a health concern if people inhale sufficient amounts.
This diagram shows the migration of the volatile organic compounds from contaminated soil and groundwater plumes into buildings. Volatile chemicals are shown to enter buildings through cracks in the foundation and openings for utility lines.
To determine if a home has a confirmed detection of TCE vapors, indoor air and crawlspace air samples are collected over a 24-hour period using a metal can called a Summa canister. The Summa canister slowly pulls air into the can under vacuum pressure.
Subslab soil gas samples are collected by drilling a small hole (approximately the size of a quarter) with a hand drill through the slab and placing a small 4-inch long metal pin (called a “vapor pin”)
through the slab. Then a tube is hooked to the pin and the tube is also connected to a Summa canister that pulls subslab gas into the can. After sampling, a small cap is placed on the vapor pin so it can be used again for the next subslab gas sampling event. The impact to the floor is the size of a quarter, and the vapor pin can be removed and the floor sealed after the last sampling event.
If your home has a confirmed detection of TCE vapors above the action level of 2 micrograms per cubic meter or 0.37 parts per billion by volume of air (ppbv), due to soil gas below your home, a mitigation system can be installed. Mitigation systems will reduce the TCE concentrations in the air. The system would pull vapors from under your foundation before they have a chance to enter your home, and release them to the outdoor air above your home where they will dilute and no longer be of health concern. This is very similar to a radon abatement system commonly used in many houses, and it operates in much the same way. If the TCE concentrations are due to sewer lines or a sump, these could be sealed to prevent vapors migrating into the house.
The most common VI mitigation system is a sub-slab depressurization system. VI mitigation is regarded as an interim action to provide human health protection until the remediation of subsurface contaminant sources is complete.
More Information on Vapor Intrusion
- ATSDR Fact Sheet -- Vapor Intrusion
- ATSDR Fact Sheet -- Investigating Vapor Intrusion
- DHSS Fact Sheet -- Facts About...Vapor Intrusion Handout
- EPA Fact Sheet -- A Citizen's Guide to Vapor Intrusion Mitigation
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