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<br />Interim Results of Quality Control Sampling <br />of Surface Water for the pper Colorado <br />River National Water-Qua ity Assessment <br />Study Unit, Water Years 1 95-96 <br /> <br />By Norman E. Spahr and Robert W. Boulger <br /> <br />Abstract <br /> <br />Quality-control samples provide part <br />of the information needed to estimate the bias <br />and variability that result from sample collection, <br />processing, and analysis. Quality-control samples <br />of surface water collected for the Upper Colorado <br />River National Water-Quality Assessment study <br />unit for water years 1995-96 are presented and <br />analyzed in this report. The types of quality- <br />control samples collected include pre-processing <br />split replicates, concurrent replicates, sequential <br />replicates, post-processing split replicates, and <br />field blanks. <br />Analysis of the pre-processing split repli- <br />cates, concurrent replicates, sequential replicates, <br />and post-processing split replicates is based on <br />differences between analytical results of the envi- <br />ronmental samples and analytical results of the <br />quality-control samples. Results of these compari- <br />sons indicate that variability introduced by <br />sample collection, processing, and handling is <br />low and will not affect interpretation of the envi- <br />ronmental data. The differences for most water- <br />quality constituents is on the order of plus or <br />minus 1 or 2 lowest rounding units. A lowest <br />rounding unit is equivalent to the magnitude of <br />the least significant figure reported for analytical <br />results. The use of lowest rounding units avoids <br />some of the difficulty in comparing differences <br />between pairs of samples when concentrations <br />span orders of magnitude and provides a measure <br />of the practical significance of the effect of <br />variability. <br /> <br />Analysis of field-blank quality-control <br />samples indicates that with the exception of chlo- <br />ride and silica, no systematic contamination of <br />samples is apparent. Chloride contamination <br />probably was the result of incomplete rinsing of <br />the dilute cleaning solution from the outlet ports <br />of the decaport sample splitter. Silica contamin~- <br />tion seems to have been introduced by the blank <br />water. Sampling and processing procedures for <br />water year 1997 have been modified as a result <br />of these analyses. <br /> <br />INTRODUCTION <br /> <br />The Upper Colorado River study unit (UCOL) <br />is 1 of 59 National Water-Quality Assessment <br />(NA WQA) study units. The long-term goals of <br />the NA WQA program are to (1) describe current <br />water-quality conditions for a large part of the <br />Nation's freshwater streams, rivers, and aquifers; <br />(2) describe how water quality is changing over time; <br />and (3) improve understanding of the primary natural <br />and human factors that affect water-quality conditions <br />(Leahy and others, 1990). Hydrologic and water- <br />quality assessments of the UCOL study unit began in <br />1994. The UCOL study unit is described by Driver <br />(1994) and Apodaca and others (1996). A network of <br />14 surface-water-quality sampling stations has been <br />established in the UCOL study unit (Spahr and others, <br />1996). Sampling for water-quality constituents began <br />at three of these sites in water year 1995, and full <br />implementation of sampling began in water year 1996. <br />Site locations are shown in figure 1. Site names and <br />station numbers are listed in table 1. The NA WQA <br /> <br />Abstract <br />