Buying or Selling Land? Important Information on Vapor Intrusion

Vapor intrusion (VI) of volatile contaminants of concern (COCs) into occupied structures is an ongoing public health concern which can seriously impact property transactions. Numerous contradictory guidelines exist which has caused confusion in the regulated community. In addition, VI research is ongoing and new discoveries are being made that are contributing to clarifying various aspects of the VI issue. To assist in mitigating confusion created by contradictory guidelines, and to update current VI guidelines, the Department of Toxic Substances Control (DTSC), the San Francisco Regional Water Quality Control Board (SFRWQCB), and the State Water Resources Control Board (SWRCB), are working together to create supplemental VI guidance, which is being referred to as the “2018 Cal/EPA VI Supplement”. This supplement will impact the way that consultants approach VI screenings and investigations, which will in turn impact costs and decision-making in the property transfer process.

The working group has created a 4-step process to protect current occupants of buildings with VI issues and to protect future occupants after the site is fully assessed. The working group contends that this will bring state-wide consistency to the process and improve risk management.
 
As presented by members of the working group at the AEHS conference in San Diego, the four steps include:
 
Step 1, Identification and Prioritization
Developing an initial Site Conceptual Model (CSM) using proximity to contaminants, evaluation of who occupies the buildings and for what purpose, and preferential pathways such as utility lines to identify which buildings should be evaluated first for VI.
 
Step 2, Soil Gas Screening
Sampling near buildings to determine if a threat to occupants exist.
 
Step 3, Indoor, Outdoor, and Sub-slab Air Sampling
For occupied buildings where a threat to occupants might exist, conducting multiple rounds of paired indoor and sub slab air sampling concurrent with outdoor air sampling.  The sub slab and outdoor air data are used to identify confounding factors.
 
Step 4, Risk Management Framework
Step 4 (the most controversial), will be a framework that will help determine when to manage risk (mitigate and/or remediate to bring down indoor air concentrations of COCs). 

​Concerns exist in the regulatory community that because subsurface and building conditions can change over time (contaminant plumes can migrate, slabs can degrade, etc),  a  conservative attenuation factor of subslab to indoor air of AF-0.03 should be used for future exposure calculations to “ensure long-term protection of human health”.

The working group hopes that these proposed steps will streamline current State guidance.
 
These guidelines have not yet been officially released but should be released soon.  Once released, the regulatory agencies will use the VI data collected using this recommended approach to generate a California-specific empirical database, which will help reduce uncertainty and improve how risk associated with VI is evaluated.

​Once the data is evaluated, the four-step process outlined above will be modified as necessary and finalized guidelines will be released before the end of 2018.

Based on this ongoing process, Alta recommends following existing guidelines, while modifying VI investigations so that they are in line with the soon to be released four-step process. This approach will improve the chances that the VI investigation will remain valid for the long-term, protecting both buyer and seller. If you are a business that has a potential issue with VI of COCs into your buildings, Alta has a team of experts that can assist you with a variety of VI issues. Contact us at info@altaenviron.com or (800) 777-0605.

Post by Mike Cassidy, Vice President of Site Assessment and Remediation