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Toxics Cleanup Program

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What is vapor intrusion?

Vapor intrusion can happen when chemicals in the shallowest groundwater evaporate and move through the soil as a gas. These vapors can potentially make their way indoors, affecting air quality in buildings above the ground.

Groundwater impacted by volatile organic compounds (VOCs) like trichloroethene (TCE) and vinyl chloride can release small amounts of vapor into the soil. The vapors rise toward the surface of the ground through gaps between soil particles. Often there is no noticeable odor because the concentrations are so low.

Specific conditions required

Under certain conditions, soil vapors that reach building foundations can move into interior building spaces. They can build up in the air inside enclosed areas, such as crawl spaces. Whether the vapors enter the building and how much they might impact indoor air quality – depends on many factors. These factors include:

  • The building’s ventilation.
  • How concentrated the groundwater contamination is.
  • Soil conditions above the water table.
  • The type of foundation a building has – slab, crawl space, or basement.
  • The integrity of a building’s foundation.

How much is too much?

Investigators can determine what effects, if any, vapor intrusion is having on indoor air quality by inspecting buildings and collecting indoor air samples.

Many common products create the same kind of air quality issues we look for when we investigate vapor intrusion. The tests we use are sensitive enough that we need to be sure the testing environment is free of things like cigarette smoke, dry cleaned clothing, certain paints, or acetone-based fingernail polish remover. We look for very small amounts of chemicals to be sure that even people who are exposed for many hours a day over many years will not be impacted by vapor intrusion. 

What is the remedy?

Typically, the solution to a vapor intrusion problem is simple: increased ventilation. Vapors are vented outside of the buildings where they become dispersed and harmless.

Next Steps

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Related links

This page created January 11, 2017