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<br />Table 10. Summary of differences between environmental and concurrent-replicate samples for generai chemical <br />constituents <br /> <br />[Lowest rounding umt is equal 10 the magmlUde of Ihe leas! significBm figurt:'J <br /> <br /> Percent 01 aamp)es Percent of samples Percent of samples <br />Constituent within plus or minus 1 within plus or minus 2 <br /> with no difference lowest rounding unit lowest rounding units <br />Calcium 29 100 100 <br />Magnesium 43 86 JOO <br />Sodium 57 71 too <br />Potas!>iull1 57 100 toO <br />Sulfate 71 J(XJ 100 <br />ChJonde 14 57 71 <br />Fluoride 86 100 100 <br />LaboT'dloryalkalinity 43 71 86 <br />Silica 43 86 86 <br />Iron 43 71 86 <br />Mangane-se 71 100 100 <br />Lab pH 57 86 86 <br />Labonuory specific conductance 14 43 71 <br />R6idue on evaporation 17 34 50 <br /> <br />rounding unit. It does not appear that the larger differ- <br />ences an~ related to sampling site or constituent <br />concenlration. Variability associated with sample <br />collection, processing. handling, shipment. and anal- <br />ysis for general chemical conslituems is low and will <br />have little effect on inlerpretation of environmenlal <br />data. <br /> <br />CQmparison of Nutrients and Organic Carbon <br /> <br />Results of comparison between environmental <br />and concurrent replicales and between environmental <br />and sequential replicates for nutrients, dissolved <br />organic carbon, and suspended organic carbon are <br />listed in table II. Shaded cells in table 11 represent <br />differences greater than plus or minus I lowest <br />rounding unit. The pattern of shaded cells indicates <br /> <br />thai the larger differences are no! related to sampling <br />site or constituent concentration. A summary of <br />the differences between the environmental and <br />concurrent-replicate samples for the constilUents in <br />table 11 is given in table 12. Sequential-replicate <br />differences are not summari1.ed because of the <br />small number of samples available. The majority of <br />the differences are within plus or minus I lowest <br />rounding unit with the exception of suspended organic <br />carbon. The majority of the suspended organic <br />carbon differences are within plus or minus 2 lowest <br />rounding units. V'lriability associated with sample <br />collection, processing, handling. shipment, and anal- <br />ysis for nutrients and organic carbon is low and will <br />have little effect on interpretation of environmental <br />data. <br /> <br />20 Interim Results 01 Quality-Control Sampling or Surface Wsterfor the Upper Colorado River National Water-Quality <br />Assessment Study Unit, Water Year'a 1995--96 <br />