The U.S. Geological Survey (USGS) has a need to communicate the significance of the water-quality findings of its National Water-Quality Assessment (NAWQA) Program in a human-health context. Historically, the USGS has assessed water-quality conditions by comparing water concentration data against established drinking-water standards and guidelines. However, because drinking-water standards and guidelines do not exist for many of the contaminants analyzed by the NAWQA Program and other USGS studies, this approach has proven to be insufficient for placing USGS data in a human-health context. To help meet this need, health-based screening level (HBSL) concentrations or ranges are being determined for unregulated compounds (that is, those for which Federal or State drinking-water standards have not been established), using a consensus approach that was developed collaboratively by the USGS, U.S. Environmental Protection Agency (USEPA), New Jersey Department of Environmental Protection, and Oregon Health & Science University. USEPA Office of Water methodologies for calculating Lifetime Health Advisory and Risk-Specific Dose values for drinking water are being used to develop HBSL concentrations (for unregulated noncarcinogens) and HBSL concentration ranges (for most unregulated carcinogens). This report describes the methodologies used to develop HBSL concentrations and ranges for unregulated compounds in State- and local-scale analyses, and discusses how HBSL values can be used as tools in water-quality assessments. Comparisons of measured water concentrations with Maximum Contaminant Level values and HBSL values require that water-quality data be placed in the proper context, with regard to both hydrology and human health. The use of these HBSL concentrations and ranges by USGS will increase by 27 percent the number of NAWQA contaminants for which health-based benchmarks are available for comparison with USGS water-quality data. USGS can use HBSL values to assist the USEPA and State and local agencies by providing them with comparisons of measured water concentrations to scientifically defensible human health-based benchmarks, and by alerting them when measured concentrations approach or exceed these benchmarks.
History of Pilot Effort and Reaching Consensus
USEPA Human Health-Based Benchmarks and Those Used by USGS
Health-Based Screening Level (HBSL) Approach
Acceptable Sources of Cancer Classifications and Toxicity Values for HBSL Development
Developing HBSL Concentrations for Unregulated Noncarcinogens
Methodology for Unregulated Noncarcinogens
Examples: Unregulated Noncarcinogens
Developing HBSL Concentrations or Concentration Ranges for Unregulated Carcinogens
Methodology for "Known," "Likely," Group A, and Group B Carcinogens
Methodology for "Suggestive Evidence" and Group C (Possible) Carcinogens
Examples: Unregulated Carcinogens
Benefits of Using HBSL Benchmarks
Use of HBSL Values as Tools in Water-Quality Assessments
Toccalino, Patricia, Nowell, Lisa, Wilber, William, Zogorski, John, Donohue, Joyce, Eiden, Catherine, Krietzman, Sandra, Post, Gloria, 2003, Development of health-based screening levels for use in State- or local-scale water-quality assessments: U.S. Geological Survey Water-Resources Investigations Report 03-4054, 22 p.
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
Download the Report (PDF, 968KB).
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Send questions or comments about this report to J.S. Zogorski (605) 394-3214.
For more information about USGS National Water-Quality Assessment Program, visit the NAWQA Program home page or more information about the USGS National Water-Quality Assessment Program Volatile Organic Compound National Syntheses, visit the VOC National Synthesis home page.
For more information about USGS activities in South Dakota, visit the USGS South Dakota Water Science Center home page.
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