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<br />Table 7. Summary of differences between environmental and pre-processing split-replicate samples for nutrients and <br />organic carbon <br /> <br />{Lowest rounding unit is equal 10 lhe magnitude of the least significant figureJ <br /> <br /> Percent of samples Percent of samples Percent of samples <br />Constituent with no difference within plus or minus 1 within plus or minus 2 <br /> lowest rounding unit lowest rounding units <br />Ammonia 71 86 100 <br />Dis1>ol ved ammonia plus organic 7\ 100 tOO <br />Total ammonia plus organic 57 86 86 <br />Nitrite 86 100 100 <br />Nitrite plus nitrate 57 100 100 <br />Dissolved orgamc carbon 14 100 100 <br />Suspended organic carbon 29 71 71 <br />Dissolved phosphorus 86 86 86 <br />Total pho.'lophorus 71 86 86 <br />Ot1hopho~phate \00 100 100 <br /> <br />Comparison of Trace Elements <br /> <br />Trace-element samples are routinely collected <br />at only two of the network sites. therefore only two <br />pre-processing split replicates were collected for <br />trace-element constituents. The environmental and <br />pre-processing split-replicate results for these samples <br />are listed in table 8. Because of the low number <br />of pairs of samples, percentage of samples within <br />ranges of rounding units are not provided. Many <br /> <br />of the trace-element concentrations are less than the <br />laboratory reporting limit (indicated by a less-than <br />value). To detemUne the differences between the <br />environmental and pre-processing split-replicate <br />sample concentrations. a value of one-half of the <br />reporting limit was substituted for the values desig- <br />nated as a "less than:' None of the differences were <br />greater than I ugfL (microgram per liter) or I lowest <br />rounding unit. <br /> <br />12 Interim Results of Quality~Control Sampling of Surface Water for the Upper COIorBdo River National Water.Quality <br />Assessment Study Unit, Water Years 1995-96 <br />