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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5027

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Glossary

Aquatic-life Benchmark Pesticide concentrations in water that, if exceeded, may be of potential concern for aquatic life. In this report, benchmarks are given for fish, benthic invertebrates, and vascular plants, for both acute and chronic exposure.

Benchmark Quotient (BQ) The ratio of a measured concentration of a detected contaminant to its benchmark, and in this report, to a USEPA drinking water standard Maximum Contaminant Level (MCL) value (for regulated compounds); Health-Based Screening Level (HBSL) value (for unregulated compounds); and Aquatic-life benchmarks when available.

Cancer Risk Concentration The drinking-water concentration associated with a specified cancer risk level (typically 1 in 10,000, 1 in 100,000, or 1 in 1,000,000), under certain exposure conditions: consumption of 2 liters of drinking water per day by a 70-kilogram body weight individual over a lifetime (70 years) (U.S. Environmental Protection Agency, 2006).

Clackamas Watershed Management Group (CWMG) A group of public agencies including Clackamas County Water Environment Services (WES) and the Clackamas River Water Providers (CRWP)—a consortium of local water agencies including the Cities of Estacada and Lake Oswego, Clackamas River Water, North Clackamas County Water Commission, South Fork Water Board, and Sunrise Water Authority—that manage or utilize water resources in the Clackamas River Watershed.

“e” coded data Pesticide concentration values that are “e” coded indicate values estimated by the laboratory because (1) certain compounds had poor recoveries or are particularly difficult to analyze, (2) sample matrix effects (highly turbid water, for example) interfered with laboratory analyses, or (3) concentrations were less than laboratory reporting levels (LRLs), resulting in reduced statistical certainty for reported concentrations. The probability of a false positive result for a pesticide detection in this study was less than 1 percent, whether the value was “e” coded or not.

Formazin Nephelometric Unit (FNU) The measurement unit for turbidity data collected by the continuous water-quality monitors in the Clackamas River. FNUs are similar to Nephelometric Turbidity Units (NTUs), the difference being the wavelength of light used to make the measurement (infrared light type instruments report in FNUs, whereas white light instruments report in NTUs). Due to the fact that suspended particles scatter light of different wavelengths with varying efficiency, FNU data often are not directly comparable to NTU data. See http://or.water.usgs.gov/grapher/fnu.html for more information.

Health-Based Screening Level (HBSL) HBSLs are benchmark concentrations of contaminants in water that, if exceeded, may be of potential concern for human health. HBSLs are nonenforceable benchmarks that were developed by the USGS in collaboration with the U.S. Environmental Protection Agency (USEPA) and others using (1) USEPA methodologies for establishing drinking-water guidelines, and (2) the most recent, USEPA peer-reviewed, publicly available human-health toxicity information (Toccalino and others, 2003; Toccalino, 2007).

Human-Health Benchmarks Benchmark concentrations used in this report to evaluate observed concentrations in finished drinking water. These include USEPA MCL values for regulated contaminants and USGS HBSL values for unregulated contaminants.

Maximum Contaminant Level (MCL) A legally enforceable drinking-water standard that sets a maximum allowable level of a particular contaminant in public water systems. MCLs are set as close as feasible to the maximum level of a contaminant at which no known or anticipated adverse effects on human health would occur, taking into account the best available technology, treatment techniques, cost considerations, expert judgment, and public comments (U.S. Environmental Protection Agency, 2006).

Nephelometric Turbidity Ratio Unit (NTRU) The measurement of turbidity reported by benchtop instruments used in this study to measure the turbidity of storm samples. This method uses a light source with a wavelength of 400-680 nanometers (nm), 90 degree detection angle, and multiple detectors with ratio compensation. See Formazin Nephelometric Unit (FNU).

Pesticide Toxicity Index (PTI) PTI values were calculated for each sample to estimate its relative toxicity by summing the toxicity quotients for each pesticide detected in a sample (or the concentration divided by the median toxicity endpoint, typically an LC₅₀ [the lethal concentration for 50 percent of the test population] for a 96-hour chemical exposure). The PTI does not, however, determine whether water in a sample is toxic (Munn and Gilliom, 2001).

Storm Event (Synoptic) Sampling A data collection effort occurring over a short period of time at a number of sites to characterize spatial conditions or provide a snapshot of conditions during target periods such as the spring pesticide application season or the first flush event in autumn. In this study, pesticide synoptic samplings occurred during spring and fall storms in 2000 and 2005.

Unregulated Pesticide Compounds As used in this report, pesticide compounds without Federal and (or) State drinking-water standards.

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