Health-Based Screening Levels (HBSL)

Health-Based Screening Levels for Evaluating Water-Quality Data

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) National Water-Quality Assessment (NAWQA) Program for contaminants without USEPA MCLs or HHBPs.

    HBSLs were updated in June 2014 in order to:
  • Provide benchmarks, when possible, for 267 new contaminants analyzed by the NAWQA Program.
  • Remove HBSLs for contaminants with new USEPA chronic HHBPs.
  • Be consistent with new USEPA policies by calculating both Noncancer and Cancer HBSLs for some contaminants.

The table below contains 777 contaminants, of which: 155 have HBSLs, 79 have MCLs, 117 have HHBPs, and 426 have no available benchmark. MCLs and HHBPs are provided for user convenience; for more information about them, and to obtain current values, please visit the USEPA websites. HHBPs listed on this website were current as of August 2013, but were updated in January 2017; this website will be updated to reflect those changes. Learn more about HBSLs and guidance on their use.


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HBSL values current as of June 30, 2014USEPA BenchmarksUSGS Benchmarks
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a This study contains Chemical Abstract Service (CAS) Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM.
b USEPA Maximum Contaminant Levels (MCLs) were current as of April 2012. Users should verify USEPA MCL values here or here.
c USEPA Human Health Benchmarks for Pesticides (HHBPs) listed on this website were current as of August 2013, but were updated in January 2017; this website will be updated to reflect those changes. Users should obtain current HHBP values here.
d See "HBSL Methods & Guidance" for guidance on the use of multiple benchmarks for a single compound.
e See "HBSL Methods & Guidance" for equations used to calculate USGS noncancer and cancer Health-Based Screening Level (HBSL) values. HBSLs were current as of Oct 26, 2017.