Guidance on the Use of Benchmarks in Screening-Level Assessments
When conducting screening-level assessments, it is important to apply the most recent guidance on the use of Health-Based Screening Levels and Maximum Contaminant Levels. Screening-level assessments provide an initial perspective on the potential significance of detected contaminants to human health and help prioritize further investigations. The most recent guidance on the use of water-quality benchmarks in screening-level assessments is provided in SIR 2007-5106, which includes information on:
- Selection of benchmarks;
- Comparison of contaminant concentrations in water to benchmarks;
- Evaluation of the potential significance of contaminant occurrence to human health; and
- Limitations of screening-level assessments
Periodic updates to the guidance provided in SIR 2007-5106 will be posted on this website
Working with stakeholders
It may be useful for USGS staff to share preliminary water-quality findings with the
appropriate Federal, State, or local drinking-water agencies prior to presenting
or publishing interpretive statements about drinking-water quality. Such
agencies have regulatory responsibilities in the area of drinking water, they
will be stakeholders in the results, and they have significant technical
expertise that can be brought to bear in assessing water-quality data in the
context of human health. When appropriate, evaluations of the potential
human-health implications of USGS water-quality information can be communicated
through jointly authored publications and (or) press releases by the agency that
has responsibility for the protection of human health. For example, the first
study that applied HBSLs to ground-water quality data was conducted in New
Jersey, and the study report (USGS
SIR 2004-5174) was co-authored by representatives of the New Jersey Department of Environmental
Protection.
Agencies responsible for the protection of human health may
be asked the following questions by their constituents:
1. Were "problems" found? Contaminants with concentrations greater than human-health benchmarks, if any, are identified.
2. Were people informed? It may be appropriate to inform a variety of stakeholders about approved water-quality results that have undergone a quality-control review. For example, water-quality results may be sent to homeowners and water utilities that provide USGS personnel access to their property and permission to sample their wells or water supplies. Letters to these stakeholders should provide resources for additional health-related information or questions. Such resources include county or state health departments, U.S. Environmental Protection Agency (USEPA) fact sheets, the Agency for Toxic Substances and Disease Registry ToxFAQs, and USEPA's Safe Drinking Water Hotline (or 1-800-426-4791). Information about working with stakeholders also may be found in USGS's 1990 policy for reporting Maximum Contaminant Level exceedances (memo 90.38).
3. Were "problems" resolved? Resolving water-quality "problems" is typically beyond the USGS's mandate. However, water-quality results can be shared with the regulatory agencies responsible for cleanup and remediation of water resources.
Examples of HBSL Applications
Several published studies have used Health-Based Screening Levels (HBSLs) to help provide an initial perspective on the potential human-health significance of contaminant concentrations in water. These studies also provide useful examples of analyses and language applied to the use of HBSLs and Maximum Contaminant Levels (MCLs) as water-quality benchmarks:
- National assessment of VOCs in ground water and a corresponding Fact Sheet about what those finding may mean to human health.
- National assessment of pesticides in streams and ground water. This assessment did not use HBSLs, but it contains examples of the application of MCL, Lifetime Health Advisory, and Cancer Risk Concentration values as water-quality benchmarks in the context of human health.
- State-scale analyses of the occurrence of anthropogenic organic compounds in ground water and finished water of community water systems in Nevada and the northern Tampa Bay area in Florida.
- Fact Sheet providing background on the HBSL effort.
- State-scale analyses that applied HBSLs to ground-water quality data in New Jersey (journal article;SIR 2004-5174). Both of these documents use HBSLs calculated using the original methodology, and not the revised methodology described in SIR 2007-5106.
- Original HBSL methodology and history of the HBSL effort.