Vapor Intrusion Regulations in California

California regulatory oversight agencies are considering more stringent standards on the evaluation of vapor intrusion data at sites with volatile organic compound (VOC) impacts to soil, soil vapor, and groundwater.  This could have far-reaching consequences for property owners.  Many property owners are already seeing more difficulty with vapor intrusion concerns and the new regulations definitely not make it any easier.

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In a nutshell, we are currently, and have been for years, using actual data collected from the site to relate soil vapor to indoor concentrations or use computational models such as the Johnson and Ettinger model to calculate a probable value for indoor air concentrations.  These sites are generally dry cleaner sites, industrial sites, or properties located nearby these types of sites.  The VOCs in question generally are trichloroethylene (TCE) and tetrachloroethylene (PCE); however, other VOCs are included in these studies as well.

Another computational modeling metric is the slab attenuation factor.  Slab attenuation factor is essentially how fast vapors move from an area below the slab into the building.  Obviously, this factor can vary widely depending on the construction of the building.  A building with a crawl space and wooden floorboards will allow vapors to move much faster than a modern concrete slab-on-grade building; obviously.

The San Francisco Regional Water Quality Control Board (RWQCB) has released several new Environmental Screening Levels (ESLs) and new vapor intrusion guidance with a lowered default screening attenuation factor to 0.03.  This attenuation factor was developed by the Federal Environmental Protection Agency (EPA) for a limited number of east coast sites and does not represent the standard construction practices employed in west coast states, let alone allow for the various fluctuations based on the construction methods employed on a given building.


{See our blog post on the new ESLs for TCE & PCE   and stay tuned for an upcoming blog post next month – a deep dive on what TCE is and why it matters so much to us}


Preston Brooks of Cox, Castle & Nicholson was interviewed by last month where he succinctly states, “Practitioners are urging the California EPA to be circumspect about the new standard because we do think that it will have a significant detrimental effect on real estate transactions, particularly on projects that have a lower margin of profitability, like affordable housing and homeless shelters.  We think that this new standard imposes unnecessary steps, cost and time delays that are unnecessary.”  Here at McAlister GeoScience, we agree.  Site-specific data and evaluations are important to say the least and we are attempting to work with the California regulatory agencies on this.

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