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CONCLUSIONS Quality-control samples provide part of the information needed to estimale the bias and variability that result from sample collection, processing, and analysis. This report discusses the qualily-control samples of surface water collected during water years 1995-96 in the UCOL study unit. Initial design of the quality-control plan incorporated the expected and measured constituenl concentrations. streamflow conditions. and land use to distribute samples within the network. Results of the analysis of pre-processing split-replicate, concurrent-replicate, sequential- replicate. and post-processing split-replicate quality- control samples indicate that variability resulting from sample collection. processing. handling. ship- ping. and analysis generally is low and will have no practical effect on environmental data interpretation. No large systematic increase in variability resulting from sample collection or processing is evident in the results of the analysis. Analysis of field-blank samples indicated that. with the exception of chloride and silica. no systematic contamination of samples is apparent. Interpretation of the chloride em;ronmental data will need to be qualified by reference to the chloride blank contamination. The silica contamina- tion was the result of silica in the blank waler and will nO! affect interpretation of environmental data. Data analysis presented in this report has resulted in the following procedural changes for sampling within the UCOL surface-water network: (I) Fully disassemble the fillings and tubing of the outlet ports of the decaport sample splitter during field cleaning and rinsing; (2) implement recording and tracking of lot numbers and certificate of analyses for water used as blank water; (3) leach dissolved organic carbon filters with at least \00 ml of organic blank water prior to processing the sample (smaller volumes were previously used); (4) process additional field blanks and replicates for trace-element constituents (few samples available to dale); and (5) tesl the effi- ciency of the field cleaning prowcol by processing blanks after tield-c1eaning equipment rather than using laboratory-cleaned equipment. These changes were implemenled in water year 1997. REFERENCES CITED Apodaca. L.E., Driver. N.E., Stephens, V.c.. and Spahr. N.E.. 1996, Environmental selting and implications on waler quality, Upper Colorado River B<Jsin, Colorado and Utah: U.S. Geological Survey Water-Resources Investigations Report 95--4263, 33 p. Driver. N .E., \994. Nation.l Water-Quality Assess- ment Progral11-Upper Colorado River Basin: U.S. Geological Survey Open-File Report 94-102. 2 p. Leahy. P.P.. Rosenshein. J.S., and Knopman. D.S.. 1990, Implementation pl;m for the National Water-Quality Assessment Program: U.S. Geological Survey Open~ File Report 90-174.10 p. Spahr, N.E.. Driver, N.E.. and Stephens.V.c., 1996. The Upper Colorado River National Water- Quality Assessment Program surface-waler- monitoring network: U.S. Geological Survey Facl Sheet FS-191-96. 4 p. U.S. Geological Survey, 1996. Water resources data, Colorado, water year I 995-v . 2. Colorado River Basin: U.S. Geological Survey W..Her-Data Report CO-95-2, 471 p. -1997, Water resources data. Colorado. water year 1996-,'.2. Colorado River Basin: U.S. Geolog- ical Survey Water-DaJa Report CO-96--2. 551 p. 34 Interim Results ot Quality-Control Sampling of Surface Water for the Upper Colorado River National Water~Quality Assessment StUdy Unit. Water Years 1995-96 ~ IJ.S. (;QVE&NHEIIT PRINTING orneE; 1991 - 67)-08) I ~0006 REGlO~ NO_ a