Vapor Intrusion is the migration of chemical vapors from the subsurface into commercial and residential buildings. Vapors can migrate through soil and into buildings through cracks in foundations, basements, crawl spaces and sewers. In February 2020, the Department of Toxic Substances Control, the San Francisco Bay Regional Water Quality Control Board, and the State Water Resources Control Board issued in draft form Supplemental Guidance: Screening and Evaluating Vapor Intrusion which recommends a consistent approach when screening buildings for subsurface vapor risk to occupants and describes a framework for deciding when cleanup and/or mitigation is needed.
The regulated community expected regulators to finalize the long-awaited Guidance, but that may be delayed now that recent studies performed by the DTSC have emerged showing that the Supplemental Vapor Intrusion Guidance may have gone too far in its estimation of risk. The delay may provide some relief to site owners due to concerns that the attenuation factors prescribed in the Guidance were too conservative and would have made it impossible to achieve closure for sites with soil vapor contamination.
- History and legal framework related to vapor intrusion
- Uncertain future of the February 2020 Draft Supplemental Guidance
- Screening Levels to evaluate potential site risks during due diligence and brownfield redevelopments, and delays in site closure
- Recent DTSC “California” VI study aimed at evaluating California-specific attenuation factors
- Legal concerns, including litigation and the enforceability of agency directives in the absence of binding regulations