In areas of known soil and groundwater contamination by solvents (VOCs) such as dry cleaning solvents, the volatile chemicals can migrate into nearby buildings, crawl spaces or other enclosed space.

The vapor intrusion risk can occur as a result of contaminated groundwater which has migrated beneath the property from an up-gradient, off-site source. These vapors present a health risk to the occupants in high concentrations.

The affected property owner usually has no responsibility for the cleanup of contamination. However, owners and lenders face potential liability from the occupants of the building and may have to take steps for mitigation of contaminated vapors.

If soil or groundwater contamination is suspected, Phase 2 soil vapor sampling is conducted using specific procedures and specially prepared samplingcontainers. Results of laboratory analysis can be compared with Regional Water Quality Control Board (RWQCB) Environmental Screening Levels (ESL).

If soil vapor results exceed these levels, indoor air sampling should be conducted by a Certified Industrial Hygienist (CIH) to evaluate the risk to occupants and potential liabilities to owners.