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 develops quality-assurance and quality-control procedures so that its water-quality data are of the highest possible quality and represent stream conditions. These procedures include personnel training, database management, cleaning equipment, blank sampling, concurrent point and cross-section sampling, concurrent replicate samples, and split replicate samples. The U.S. Geological Survey and Gwinnett County Watershed Monitoring program require one of two methods when collecting water-quality samples: the Equal-Width Increment (EWI) method or automatic point sampler method. In order to obtain a representative sample during a storm, it is preferable to collect samples using the EWI method. This method collects several points along the stream cross section and at several times during the storm hydrograph. Because of the large labor requirements and difficulty in sampling storm flows consistently, EWI samples are often not practical; an alternative is to obtain a composite sample that represents the entire hydrograph using an automatic point sampler. The USGS uses quality-assurance and quality-control procedures in the Gwinnett County Watershed Monitoring program to assure that automatic point samples provide accurate, uncontaminated, and representative EWI samples.
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