USGS Fact Sheet FS-026-98
Quality Control at the U.S. Geological Survey National Water Quality Laboratory
Kimberly D. Pirkey and Stephen R. Glodt
April 1998
The National Water Quality Laboratory (NWQL) — the primary analytical facility of the U.S. Geological Survey (USGS) — analyzes environmental samples from across the United States and around the world. Samples of water, sediment, aquatic biological materials, and air are analyzed at the laboratory using state-of-the-art instruments and methods. These analyses require a comprehensive quality-assessment process.
Quality assessment consists of two separate but related components: quality-control data and quality-assurance elements. Quality-control (QC) data are produced to measure bias and variability of the analytical method. With QC data, the magnitude of errors, and thus the quality of the environmental data, is not known. Some examples of QC data sample types include standard reference materials, laboratory replicates, laboratory reagent blanks, spikes, and surrogates. Assessment of QC data is essential to evaluating environmental analytical data produced by the laboratory. Definitions of QC data sample types used by the NWQL are emphasized in this Fact Sheet.
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