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IDEM > Your Environment > Vapor Intrusion > Vapor Intrusion: Definitions Vapor Intrusion: Definitions

Ambient Air Sample
An outdoor air sample that is representative of the air surrounding a home or building.
Biodegradation
Decomposition of soil gas into other compounds by the action of micro-organisms that exist in the soil.
Breathing Zone
Defined as the area from 3 – 5 feet above the ground, lower if small children are present. Indoor Air samples should be taken from this zone to insure that they are representative of the air being breathed in the building.
BTEX
An acronym that stands for "Benzene, Toluene, Ethylbenzene and Xylene." These compounds are major components of gasoline and are commonly used to indicate the presence of gasoline contamination. BTEX readily biodegrades in soil.
Chlorinated Compounds
These include chemicals such as PCE (also know by its chemical name tetrachloroethene) and TCE (also known by its chemical name trichloroethene) that are commonly used in dry cleaning and industrial operations. These chemicals can breakdown into others which may also be of concern for vapor intrusion. They do not readily biodegrade in subsurface soil and may require active remediation to remove.
Cracks
A fracture, often a narrow opening in the cement floor or foundation of a building that can provide a means for soil vapor to enter a home or building.
Indoor Air Sample
An air sample taken from within the living or work space of a home or building that is used to determine the concentration of the chemical that may be inhaled.
Preferential Pathway
A subsurface feature that exists below ground as a fracture, utility line, or pipeline though which soil gas moves more easily than through the natural soil.
Soil Gas Sample
An air sample taken from the air in the soil pore spaces. Soil gas samples are used to characterize chemical concentrations in the soil.
Sub-Slab Sample
An air sample collected immediately beneath a home or building with a basement foundation and/or a slab-on-grade. Sub-slabs are collected to determine the concentration of chemicals in the soil vapor beneath a home or building because these chemicals may enter the building.
Summa Canisters
An airtight, stainless-steel container which is used to collect air samples. Summa canisters are evacuated and used under vacuum to take indoor air, ambient air or soil air vapor samples.
Vapor Intrusion (Radon) Mitigation System
A mechanical device(s) that applies a low amount of suction immediately below the foundation or the occupied space of the building and collects soil vapors which are then vented to the outside. For more information on how these systems operate, please see the IDEM Web page "How Do You Get Radon Out of a Building?"