Health‐Based Screening Levels to Evaluate U.S. Geological Survey Ground water Quality Data

Abstract

Federal and state drinking-water standards and guidelines do not exist for many contaminants analyzed by the U.S. Geological Survey's National Water-Quality Assessment Program, limiting the ability to evaluate the potential human-health relevance of water-quality findings. Health-based screening levels (HBSLs) were developed collaboratively to supplement existing drinking-water standards and guidelines as part of a six-year, multi-agency pilot study. The pilot study focused on ground water samples collected prior to treatment or blending in areas of New Jersey where groundwater is the principal source of drinking water. This article describes how HBSLs were developed and demonstrates the use of HBSLs as a tool for evaluating water-quality data in a human-health context. HBSLs were calculated using standard U.S. Environmental Protection Agency (USEPA) methodologies and toxicity information. New HBSLs were calculated for 12 of 32 contaminants without existing USEPA drinking-water standards or guidelines, increasing the number of unregulated contaminants (those without maximum contaminant levels (MCLs)) with human-health benchmarks. Concentrations of 70 of the 78 detected contaminants with human-health benchmarks were less than MCLs or HBSLs, including all 12 contaminants with new HBSLs, suggesting that most contaminant concentrations were not of potential human-health concern. HBSLs were applied to a state-scale groundwater data set in this study, but HBSLs also may be applied to regional and national evaluations of water-quality data. HBSLs fulfill a critical need for federal, state, and local agencies, water utilities, and others who seek tools for evaluating the occurrence of contaminants without drinking-water standards or guidelines.

Status and understanding of groundwater quality in the Bear Valley and Lake Arrowhead Watershed Study Unit, 2010: California GAMA Priority Basin Project

“…An RC is defined as the ratio of a constituent's concentration measured in a groundwater sample to the concentration of a constituent's regulatory or non-regulatory benchmark used to evaluate drinking-water quality. The use of RCs is similar to approaches employed by other studies to place the concentrations of constituents in groundwater in a toxicological context (for example, U.S. Environmental Protection Agency, 1986;Toccalino and others, 2004;Toccalino and Norman, 2006;Rowe and others, 2007).…”

“…Additional information on the types of benchmarks and listings of the benchmarks for all constituents analyzed is provided by Mathany and Belitz (2013). Toccalino and others (2004), Toccalino and Norman (2006), and Rowe and others (2007) used the ratio of measured sample concentration to the benchmark concentration, either MCL-US or HBSL, and defined this ratio as the benchmark quotient (BQ). The term RC is used in this report rather than BQ because these 2 benchmark values are not the same for the 20 constituents that have MCL-CA values that differ from their MCL-US values or for the 11 constituents that neither have MCL-US nor HBSL values.…”

Groundwater quality in the Western San Joaquin Valley study unit, 2010: California GAMA Priority Basin Project

“…However, untreated groundwater that does not meet regulatory standards must be treated before it is used for public drinking water supply; thus, the RC provides a quick comparative tool for identifying groundwater resources that may require treatment before use as drinking water supplies. The use of RCs is similar to the approaches used in other studies to place the concentrations of constituents in groundwater in a toxicological context (for example, Toccalino and others, 2004;Toccalino and Norman, 2006;Rowe and others, 2007;U.S. Environmental Protection Agency, 2014).…”

“…Additional information about the types of benchmarks used and lists of the benchmark values for all constituents analyzed are provided by Mathany and others (2013). Toccalino and others (2004), Toccalino and Norman (2006), and Rowe and others (2007) used the ratio of measured sample concentration to the benchmark concentration, either the EPA MCL or the EPA and USGS health-based screening level (HBSL), and defined this ratio as the benchmark quotient (BQ). Because different water-quality benchmarks were used to calculate the RCs and BQs, the terms are comparable, but not interchangeable.…”

Status and understanding of groundwater quality in the Northern Coast Ranges study unit, 2009: California GAMA Priority Basin Project

“…Toccalino and others (2004), Toccalino and Norman (2006), and Rowe and others (2007) previously used the ratio of measured sample concentration to the benchmark concentration [either MCL-US or health-based screening levels (HBSLs)] and defined this ratio as the benchmark quotient. HBSLs were not used in this report because HBSLs are not currently used as benchmarks by California drinkingwater regulatory agencies.…”