Vapor Intrusion in the Regulatory Community: How ESTCP is Impacting Investigations

Environmental Screening Levels (ESLs) are concentrations for groundwater, soil, soil gas, and indoor air derived by the San Francisco Bay Regional Water Quality Control Board for over 100 chemicals to allow direct comparison to environmental sample data collected at contaminated sites. The ESLs are developed to help the San Francisco Bay Regional Water Board (RWB) staff protect water quality in the region. In early 2019, the San Francisco Bay Regional Water Quality Control Board released a  User’s Guide that explained how these ESLs are derived and how they should and should not be used.  The User’s Guide provides a regulatory basis for the ESLs, their history and use, a comparison to other available screening levels, the RWB’s approach to site closure evaluations, and other technical documents for use in combination with the ESLs. In Section 5.4.1 (Vapor Conduit Pathway Evaluations: Sewer/Utility Conduit Air), the Guidance recommends usage of the  Investigation Protocol developed by Dr. Thomas McHugh from GSI Environmental, Inc. and his team under ESTCP project  ER-201505 until formal regulatory agency guidance is developed.

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Although the sewer and utility tunnel pathways are often mentioned in regulatory guidance documents, there is little information detailing the conceptual model or assessment methods. Dr. McHugh and his team addressed this issue during their ESTCP project by obtaining a better understanding of sewers and utility tunnels as preferential pathways for vapor intrusion (VI). Through identifying risk factors and studying the  conceptual model, the project team developed and validated an investigation protocol that provides a standardized framework for evaluating sewers and utility tunnels as potential preferential pathways for VI. The protocol includes initial desktop screening to classify sites as higher or lower risk and recommends early field testing of sewers and utility tunnels for higher risk sites and conventional VI investigation (including indoor air testing) for lower risk sites. More detailed results from this demonstration are available in the project’s  Final Report.

To learn more about this and other projects focused on vapor intrusion, visit  SERDP and ESTCP's web site.

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