The United States Geological Survey (USGS) operates laboratories for the analysis of physical characteristics of natural water bodies, including fluvial sediment. Sediment laboratories, producing data for the USGS, determine suspended-sediment concentration (SSC), fine/sand separation, and particle size distribution (PSD). The usefulness of these data is dependent on the accuracy and reliability of laboratory analyses. To ensure the physical sediment data produced or used by the USGS are of a known quality and are sufficient to provide long-term comparability and consistency on a national basis, the USGS initiated the Sediment Laboratory Quality Assurance (SLQA) Project in August 1996. To improve and assess data quality produced by the USGS and to enable comparison among laboratories, participation in the SLQA Project by USGS sediment laboratories and by laboratories contracted by the USGS is required. Results from the SLQA studies may be used to assess variability in environmental data and to improve laboratory performance.
Annually, two single-blind SLQA studies are conducted. Participating laboratories are asked to determine suspended sediment concentration, sediment mass, separation of fine- and sand-size material, and particle size distribution using the standard techniques with which they analyze environmental samples. Laboratories are asked to only submit results for analyses they routinely perform. Currently (2019) twenty-one federal, state, contract, and private laboratories participate in the SLQA. Sediment Laboratory QA data may be accessed through this web site.
The SLQA project also prepares double-blind reference samples. This enables the submission of disguised quality control sediment-water samples with environmental samples to laboratories for analysis. The quality control samples are formulated with similar characteristics as the environmental samples with which they are submitted. Analyses of double blind samples provide a measure of bias and variability due to laboratory methods, which may be used to quantify data quality for the accompanying environmental samples. Double-blind samples have also been used for comparing analytical techniques and improving collection methods.
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