When assessing the environmental conditions of a property, you should not only be aware of what you can see at the surface but also what may reside within the subsurface as well. Contamination from spills or leaks may not only impact soil and groundwater but they can also volatilize into a vapor phase and migrate into occupied structures.

What is Vapor Intrusion?

Vapor intrusion occurs when vapor forming contaminants from a subsurface source migrate into an overlying structure. These vapors typically enter buildings through openings for utility lines, crawl spaces, and cracks in a foundation or basement wall.

What are VOCs?

The type of contaminants most commonly encountered during vapor intrusion investigations includes a class of chemicals that are capable of evaporating at room temperature known as Volatile Organic Compounds (VOCs).

Common VOCs include solvents such as Trichloroethylene (TCE) which is often associated with dry cleaning fluid and manufacturing and chemicals associated with petroleum products such as Benzene, Toluene, Ethylbenzene and Xylenes (BTEX) which are found together in gasoline.

How Do VOCs Get Into the Ground?

VOCs can enter the subsurface in a number of ways including leaking underground storage tanks, pipeline failures, spills, dumping and other kinds of releases.

Once in the subsurface, contaminants migrate downward through overlying soils eventually reaching the water table where the contaminants move in the direction of groundwater flow. If present, VOCs begin to volatilize and in this vapor phase can migrate through subsurface soils following the path of least resistance such as utility line trenches or seeping directly into a structure by way of a basement, crawl space or cracks.

What are the Concerns with Vapor Intrusion?

Harmful concentrations of VOCs can be present inside a structure before being noticed by odors. In extreme cases, these vapor phase chemicals can accumulate in homes or other occupied structures at concentrations capable of:

  • Near-term hazards such as an explosion
  • Acute short and long term health effects


Evaluating a home or other structure for the presence of vapor intrusion is often conducted when the structure is located near or above an area of contaminated soil and/or groundwater.  Testing for vapor intrusion typically involves the collection of one or more soil vapor samples by an environmental professional. A small hole is bored through the basement floor and a sample of the soil vapors is extracted using specialized equipment and sent to a certified laboratory for the analysis of VOCs. If the analysis shows VOCs are present above the applicable regulatory levels then indoor air testing may also be necessary.


If testing confirms the presence of potentially harmful levels of VOCs, a mitigation system using subsurface depressurization can be installed at the property. These systems are similar to those used for venting radon gas and can inhibit the entry of harmful VOCs into the building by continuously venting the contaminated air. The vapors extracted by the system are pulled from beneath the structure, directed through an activated carbon canister (to treat the vapors) then discharged to the atmosphere.

Contact GSI Environmental Today

If you believe your home or business may be affected by vapor intrusion, the experts at GSI Environmental can help you evaluate and cost-effectively remediate vapor intrusion at your site.  Learn more about our vapor intrusion evaluation services by calling 717-691-9799 or by filling out our contact form.