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Health-Based Screening Levels for Evaluating Water-Quality Data

April 22, 2024

Federal drinking-water standards or guidelines are not available for many of the hundreds of contaminants analyzed by the U.S. Geological Survey (USGS) in sources of drinking water. To supplement federal drinking-water standards and guidelines, the USGS began an interagency pilot effort in 1998 to develop non-enforceable Health-Based Screening Levels (HBSLs) that would help communicate the potential relevance of water-quality findings from the USGS National Water Quality Program, National Water-Quality Assessment (NAWQA) Project in a human-health context.

Health-Based Screening Levels (HBSLs) are non-enforceable water-quality benchmarks that can be used to (1) supplement U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) and Human Health Benchmarks for Pesticides (HHBPs), (2) determine whether contaminants found in surface-water or groundwater sources of drinking water may indicate a potential human-health concern, and (3) help prioritize monitoring efforts. HBSLs were developed by the U.S. Geological Survey (USGS), historically by the National Water-Quality Program (NWQP) for contaminants without USEPA MCLs or HHBPs.

HBSLs were updated in January 2024 (or April 2024, for PFAS chemicals) in order to:

  • Update toxicity information and benchmarks for the 835 contaminants included in the online searchable HBSL database, including 10 contaminants with HBSLs added since the last (2018) update.
  • Update all HBSLs to be consistent with new USEPA methods and exposure assumptions.
  • Replace HBSLs for 4 contaminants that have new USEPA HHBPs.
  • Add MCLs, proposed MCLs or develop HBSLs for 27 per- and perfluoroalkyl substance (PFAS) compounds, which are newly added to the HBSL database.