Quality-assurance data for routine water analysis in the laboratories of the US Geological Survey for water-year 1984

The U.S. Geological Survey maintains a quality-assurance program based on the analysis of reference samples for its two water-analysis laboratories located in Atlanta, Georgia, and Denver, Colorado. Reference samples containing selected inorganic constituents are prepared at the U.S. Geological Survey's Ocala, Florida, office, disguised as routine samples, and sent daily or weekly, as appropriate, to each laboratory through other U.S. Geological Survey offices. The results are permanently stored in the National Water Data Storage and Retrieval System (WATSTORE), the U.S. Geological Survey's data base for all water data. These data are analyzed statistically for precision, bias, and comparability. The results of these statistical analyses are presented for data collected during the 1984 water year. Nutrient samples, simulated-precipitation (low-concentration level) samples, and selected pesticide samples also were submitted as samples of unknown concentrations. The results of these determinations were statistically analyzed for comparability and these data are presented.

An overall evaluation of the data for water year 1984 indicated a lack of precision in the Atlanta laboratory for the determination of five constituents and in the Denver laboratory for seven constituents. A biased condition existed in the determination of twenty common constituents at both laboratories. Finally, if any constituent determined by ICP indicated bias, it tended to be positive.