CalEPA Vapor Intrusion Screening Level Update

This blog post provides a quick summary of human health screening levels for California risk assessments, including recent updates:  

• Updated DTSC Screening Levels (HERO Note 3) – released April 2019
  https://dtsc.ca.gov/wp-content/uploads/sites/31/2019/04/HHRA-Note-3-2019-04.pdf
• Updated USEPA Regional Screening Levels (RSLs) – released November 2018
  https://www.epa.gov/risk/regional-screening-levels-rsls
• Updated RWQCB-SF Bay Environmental Screening Levels (ESLs) – released January 2019, Revision 1
  https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/esl.html
• Decision criteria for use of the various agency screening levels

The USEPA, DTSC, RWQCB, and OEHHA are all recommending the use of the USEPA attenuation factor of 0.03. Please take this attenuation factor into consideration for project planning purposes. Although this empirical attenuation factor of 0.03 is based on residential, CalEPA agencies (DTSC, OEHHA, and RWQCB) are applying the attenuation factor for all land uses including commercial. Additionally, there is no longer a separate attenuation factor used for sub-slab vapor data, the empirical attenuation factor of 0.03 should be applied to sub-slab vapor data and soil vapor data collected at depth.

According to April 2019 DTSC HERO Note 3, DTSC recommended default attenuation factors for preliminary screening evaluations can be found in Table 2 of DTSC’s 2011 Vapor Intrusion Guidance. However, DTSC also recommends that screening assessments evaluate the USEPA default attenuation factors of 0.03 for sub-slab soil gas and “near-source” exterior soil gas. It is recommended that you contact the DTSC site toxicologist to ensure appropriate use of air screening levels on a site-specific basis.

The DTSC-Modified soil gas and groundwater Johnson and Ettinger (J&E) models to predict theoretical indoor air concentrations from soil gas and groundwater data have been removed from HERO’s website. The J&E models have been removed since they have not been updated and are not based on the most current J&E model spreadsheet tool from USEPA. The USEPA J&E model can be found at the following website:
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https://www.epa.gov/vaporintrusion/epa-spreadsheet-modeling-subsurface-vapor-intrusion
 
On a project-specific basis and with consultation with oversight agency, there may be a conceptual site model and site-specific empirical data to support the use of site-specific attenuation factors.  ​