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Beware of New Environmental Sc...

Beware of New Environmental Screening Levels

By Kirk Tracy

In January (2019), the San Francisco Bay Regional Water Quality Board (“Water Board”) published new Environmental Screening Levels (“ESLs”) for over 100 chemicals found at sites with contaminated soil and groundwater, an update from the prior ESLs published in 2016. Per the Water Board, the “ESLs address a range of media (soil, groundwater, soil gas, and indoor air) and a range of concerns (e.g., impacts to drinking water, vapor intrusion, and impacts to aquatic habitat).”[1] ESLs are typically used by the Water Board to determine whether additional investigation is required at the site.  However, achieving regulatory site closure does not necessarily require reducing all contaminant levels to below the respective ESLs. Indeed, the Water Board notes that the information provided in its ESL documents “is not intended to establish policy or regulation.”[2]  Further, the ESL User’s Guide indicates that “the presence of a chemical at concentrations in excess of ESL does not necessarily indicate adverse effects on human health or the environment, rather that additional evaluation is warranted” and that “ESLs should not be used as criteria to determine when chemical concentration at a site must be reported to a regulatory agency.”[3]

The new numbers include significant reductions for screening levels of tetrachloroethene (“PCE”) and trichloroethene (“TCE”). PCE is a chemical often associated with and found present in the soil and groundwater at the sites of dry-cleaners, where PCE has been used as a cleaning solvent for decades, and both PCE and TCE are associated with used as a metal degreaser in various businesses, amongst other uses. A summary of the updates to the “Tier 1” ESLs for PCE and TCE are:

Water Board’s

Tier 1 ESLs for PCE[4]

Groundwater (µg/L) Soil (mg/kg) Sub-slab Vapor (µg/m3) Indoor Air (µg/m3)
2016 3.0 0.42 240 0.48
2019 0.64 0.08 15 0.46


Water Board’s

Tier 1 ESLs for TCE[5]

Groundwater (µg/L) Soil (mg/kg) Sub-slab Vapor (µg/m3) Indoor Air (µg/m3)
2016 5.0 0.46 240 0.48
2019 1.2 .085 16 .048


Of further note, the Water Board is working with the State Water Resources Control Board, the Department of Toxic Substances Control (DTSC), and the Office of Environmental Health Hazard Assessment (OEHHA) to develop a supplemental vapor intrusion guidance document for conducting uniform vapor intrusion evaluations in California. The supplemental guidance is expected to provide information on the following topics:

  • Soil gas, subslab, indoor air, and outdoor air sampling recommendations to understand spatial and temporal variability
  • Sewers as a potential migration route and pathway of exposure
  • Recommendations for use of USEPA 2015 attenuation factors for screening
  • Risk management framework for vapor intrusion
  • Development of a California-specific vapor intrusion database[6]

The supplemental vapor intrusion guidance is anticipated for release as draft for public comment during 2019, with further information available on the State Board Vapor Intrusion Webpage at:


It should also be noted that not all regions for the Water Board have adopted these more restrictive ESLs. The new ESLs will certainly impact due diligence and real estate transactions across the San Francisco Bay Area, if not the whole state.

[1] https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/esl.html

[2] Id.

[3] User’s Guide: Derivation and Application of Environmental Screening Levels (ESLs), at 3, available at https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/ESL/ESL%20Users%20Guide_22Feb16.pdf

[4] See ESL Workbook at: https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/ESL/ESL_Workbook_Interim%20Final_24Jan19_Rev1%20(1).xlsx.

[5] See ESL Workbook at: https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/ESL/ESL_Workbook_Interim%20Final_24Jan19_Rev1%20(1).xlsx.

[6] Id.

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