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Volatile Organic Compounds in Indoor Air
Volatile organic compounds (VOCs) may arise in indoor air from sources other than vapor intrusion, so the presence of a VOC is not necessarily proof that vapor intrusion is of concern.
Because of the potential for VOCs to exist in indoor air from multiple sources, it is often useful to compare indoor air measurements to concentrations that have been observed in buildings that are not known to be impacted by vapor intrusion, and which may be thought of as typical “background”.
Sources of Indoor Air Contamination
Information on common household products that cause measureable levels of VOCs in indoor air can be found in the National Institutes of Health Household Products Database.
Background Concentrations of VOCs in Indoor Air
Dawson HE and McAlary T. 2009. A compilation of statistics for VOCs from post-1990 indoor air concentration studies in North American residences unaffected by subsurface vapor intrusion. Ground Water Monitoring and Remediation, 29(1): 60-69.
- Indoor Air Background Data
Includes a list of reference of documents regarding background indoor air data and links to each document.
- Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences.
Literature Review and Implications for Vapor Intrusion Assessment. Helen Dawson, Ph.D. U.S. EPA, Region 8, Denver, Colo. Vapor Intrusion Workshop – AEHS Spring 2008, San Diego, CA.
The Indoor Environment Department of the Environmental Energy Technologies Division (EETD) in the E.O. Lawrence Berkeley National Laboratory (LBNL)
- Hodgson AT and Levin H. 2003. Volatile organic compounds in indoor air: a review of concentrations measured in North American since 1990. Revised October 2003. LBNL-51715.
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Comparing Site to Background
In performing a comparison of site levels to "background" or “ambient” levels, it is important to understand that both site levels and background levels are characterized by distributions, and that a comparison must be based on sound statistical techniques. Useful guidance for how to conduct statistical comparisons of site data to background includes:
- Guidance for Comparing Background and Chemical Concentrations in Soil for CERCLA Sites (PDF) (89 pp, 1.3 MB)(OSWER 9285.7-41, September 2002)
- Performance of Statistical Tests for Site Versus Background Soil Comparisons When Distributional Assumptions Are Not Met (PDF) (56 pp, 1.4 MB) EPA/600/R-07/020, March 2007
If the measured level of a chemical is not statistically higher than the level that would be expected for that chemical based on background levels, then it may be concluded that the site-related contribution for that chemical is sufficiently minor that further quantitative evaluation is not needed. If the chemical is observed to be present at a level higher than would otherwise be expected, then it is appropriate to retain that chemical for quantitative risk evaluation.
EPA's Indoor Air Quality (IAQ) webpage provides information and links to resources on sources of air pollution in homes and offices, and addressing indoor air quality in public and commercial buildings.