Analysis of Quality-Assurance and Quality-Control Procedures for an Urban Water-Quality Monitoring Program, Gwinnett County, Georgia

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Knaak, Andrew E.
Ankcorn, Paul D.
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The U.S. Geological Survey has, during many years of environmental monitoring, developed quality-assurance and quality-control procedures to assist in the collection of accurate and representative water-quality data. Urban storm sampling typically is performed using one of two methods; the equal-width-increment method or the automated-point-sample method. Quality-control data (equipment blanks and concurrent samples) were collected from 1997 to 2006 at 12 watersheds in Gwinnett County, Georgia, to compare these methods and to evaluate the cleanliness of field procedures. Constituent concentrations in samples collected concurrently using both methods were compared to determine how representative point sample data were of cross-sectional stream conditions. Percent differences of concurrent-sample constituent concentrations were compared with storm size to identify bias or trend when collecting samples using the automated point-sample method. Data collected using the two different methods indicated that constituent concentrations in concurrent samples generally were within 10 percent. Constituent concentrations in equipment blanks typically were less than analytical method detection limits.
Sponsored and Organized by: U.S. Geological Survey, Georgia Department of Natural Resources, Natural Resources Conservation Service, The University of Georgia, Georgia State University, Georgia Institute of Technology
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