A state-scale pilot effort was conducted to evaluate a Health-Based Screening Level (HBSL) approach developed for communicating findings from the U.S. Geological Survey (USGS) National Water-Quality Assessment Program in a human-health context. Many aquifers sampled by USGS are used as drinking-water sources, and water-quality conditions historically have been assessed by comparing measured contaminant concentrations to established drinking-water standards and guidelines. Because drinking-water standards and guidelines do not exist for many analyzed contaminants, HBSL values were developed collaboratively by the USGS, U.S. Environmental Protection Agency (USEPA), New Jersey Department of Environmental Protection, and Oregon Health & Science University, using USEPA toxicity values and USEPA Office of Water methodologies. The main objective of this report is to demonstrate the use of HBSL approach as a tool for communicating water-quality data in a human-health context by conducting a retrospective analysis of ground-water quality data from New Jersey. Another important objective is to provide guidance on the use and interpretation of HBSL values and other human-health benchmarks in the analyses of water-quality data in a human-health context.
Ground-water samples collected during 1996-98 from 30 public-supply, 82 domestic, and 108 monitoring wells were analyzed for 97 pesticides and 85 volatile organic compounds (VOCs). The occurrence of individual pesticides and VOCs was evaluated in a human-health context by calculating Benchmark Quotients (BQs), defined as ratios of measured concentrations of regulated compounds (that is, compounds with Federal or state drinking-water standards) to Maximum Contaminant Level (MCL) values and ratios of measured concentrations of unregulated compounds to HBSL values. Contaminants were identified as being of potential human-health concern if maximum detected concentrations were within a factor of 10 of the associated MCL or HBSL (that is, maximum BQ value (BQmax) greater than or equal to 0.1) in any well type (public supply, domestic, monitoring). Most (57 of 77) pesticides and VOCs with human-health benchmarks were detected at concentrations well below these levels (BQmax less than 0.1) for all three well types; however, BQmax values ranged from 0.1 to 3,000 for 6 pesticides and 14 VOCs. Of these 20 contaminants, one pesticide (dieldrin) and three VOCs (1,2-dibromoethane, tetrachloroethylene, and trichloroethylene) both (1) were measured at concentrations that met or exceeded MCL or HBSL values, and (2) were detected in more than 10 percent of samples collected from raw ground water used as sources of drinking water (public-supply and (or) domestic wells) and, therefore, are particularly relevant to human health.
The occurrence of multiple pesticides and VOCs in individual wells also was evaluated in a human-health context because at least 53 different contaminants were detected in each of the three well types. To assess the relative human-health importance of the occurrence of multiple contaminants in different wells, the BQ values for all contaminants in a given well were summed. The median ratio of the maximum BQ to the sum of all BQ values for each well ranged from 0.83 to 0.93 for all well types, indicating that the maximum BQ makes up the majority of the sum for most wells. Maximum and summed BQ values were statistically greater for individual public-supply wells than for individual domestic and monitoring wells.
The HBSL approach is an effective tool for placing water-quality data in a human-health context. For 79 of the 182 compounds analyzed in this study, no USEPA drinking-water standards or guidelines exist, but new HBSL values were calculated for 39 of these 79 compounds. The new HBSL values increased the number of detected pesticides and VOCs with human-health benchmarks from 65 to 77 (of 97 detected compounds), thereby expanding the basis for interpreting contaminant-occurrence data in a human-health context.
Purpose and Scope
Need for and History of the Human-Health Pilot Effort
Development and Use of Health-Based Screening Level Values
Description of Study Area
Design of Public-Supply Well Network
Design of Domestic-Well Networks
Design of Monitoring-Well Networks
Analytical Considerations for Ground-Water Quality Data
Minimum Reporting Levels and Estimated Concentrations
Interpreting Detection Frequencies
Minimum Reporting Levels Compared to Human-Health Benchmarks
Guidance for Interpreting Water-Quality Data in a Human-Health Context
Step 1: Identify Human-Health Benchmarks and Compare to Measured Concentrations
Tier 1 - Benchmarks for Regulated Compounds
Tier 2 - Benchmarks for Unregulated Compounds
Step 2: Identify Contaminants of Potential Human-Health Concern Using Benchmark Quotients
Step 3: Interpret the Occurrence of Contaminants of Potential Human-Health Concern
Assessment of Ground-Water Quality in New Jersey
Step 1: Human-Health Benchmarks Identified and Compared to Measured Concentrations
Tier 1 - Regulated Pesticides
Tier 2 - Unregulated Pesticides
Volatile Organic Compounds
Tier 1 - Regulated Volatile Organic Compounds
Tier 2 - Unregulated Volatile Organic Compounds
Step 2: Contaminants of Potential Human-Health Concern Identified
Step 3: Occurrence of Contaminants of Potential Human-Health Concern Interpreted
Magnitude of BQ Values and Detection Frequency
Well Type and Use of Water
Occurrence by Well Type
Occurrence by Aquifer
Occurrence by Land Use
Contaminant Sources and Physicochemical Properties
Patterns of Occurrence of the Contaminants of Potential Human-Health Concern
Pattern 1: BQmax Greater than or Equal to 1 and Frequently Detected
Pattern 2: BQmax Greater than or Equal to 1 and not Frequently Detected
Pattern 3: BQmax Less than 1 but Greater than or Equal to 0.1 and Frequently Detected
Pattern 4: BQmax Less than 1 but Greater than or Equal to 0.1 and not Frequently Detected
Health-Based Comparison of Wells with Multiple Contaminants
Benchmark Quotient Computations for Multiple Contaminants in Individual Wells
Occurrence of Multiple Contaminants by Well Type
Occurrence of Multiple Contaminants by Aquifer and Land Use
Benefits of Applying Health-Based Screening Levels to Water-Quality Data
1. U.S. Environmental Protection Agency and New Jersey MCL values (current as of August 2004) for regulated pesticides and VOCs analyzed in ground-water samples from the Long Island-New Jersey Study Unit
2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs analyzed for in ground-water samples from the Long Island-New Jersey Study Unit
3. Unregulated pesticides and VOCs analyzed in ground-water samples from the Long Island-New Jersey Study Unit that have no human-health benchmarks (as of August 2004)
Toccalino, P.L., Norman, J.E., Phillips, R.H., Kauffman, L.J., Stackelberg, P.E., Nowell, L.H., Krietzman, S.J., and Post, G.B., 2004, Application of health-based screening levels to ground-water quality data in a state-scale pilot effort: U.S. Geological Survey Scientific Investigations Report 2004-5174, 64 p.
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Send questions or comments about this report to the author, P.L. Toccalino (503) 748-1083.
For more information about USGS activities in South Dakota, visit the USGS South Dakota Water Science Center.
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, vist the VOC National Systhesis home page.
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