Unacceptable risks for VIAP include long term chronic risks, immediate threats to safety (e.g., fire or explosion potential from vapors or methane) and short-term adverse health effects (acute) from inhalation of toxic chemicals. The potential for immediate threats to occur is often the greatest after a new release but all risks should be evaluated in the investigative process for buildings within the lateral inclusion zone (LIZ).
Note: If odors are detected or combustible, explosive, or O2-deficient conditions are found to exist inside a building, first responders should be contacted immediately. Chemicals with acute inhalation health effects may exceed acceptable air concentrations, with no other indications, therefore indoor air sampling will be necessary to make this determination.
Unacceptable risks are possible and need to be evaluated or mitigated under the following conditions:
- Sub-slab soil vapor has been identified above site-specific volatilization to the indoor air criteria (SSVIAC) or screening levels. For chemicals with identified acute health effects, unacceptable risks are possible from a single sampling event; however unacceptable risks for chemicals with chronic health effects would be possible after consistent and multiple sampling events above SSVIAC or screening levels,
- Odors or chemical concentrations above acceptable indoor values have been identified within a building, or
- A vapor source has entered a building or an underground conduit that can transport vapor directly to a building.
Additional Information is provided in Attachment A.3 on the acute vapor risks associated with VIAP and Volume 6 – Volatilization to the Indoor Air Criteria.
Indoor air sampling is the best measure of chemical concentration at the point of exposure for human health. Acceptable air concentrations, which are risk-based levels in indoor air that are the basis for developing screening levels and criteria, are provided in Volume 6 to compare indoor air sampling results. Given the variability of indoor air concentrations, this should not be used as a single line of evidence, and generally one (1) sampling event is insufficient to fully evaluate all risks.
Note: RRD does not regulate all sources of indoor air contamination. RRD regulates the volatilization of hazardous substances into indoor air from the subsurface at contaminated sites as a result of a release of hazardous substances to the environment. Therefore, when sampling indoor air, it is recommended to collect sub-slab soil gas samples to determine what chemicals of concern from the release are regulated by RRD in the indoor air.