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<br />April Monthly Report - 2002 <br />Page 3 <br /> <br />Mainstem Stream Monitoring and Reference Point Stream Monitoring <br />Sunnyside sampled the reference point (A-72) and the three main-stem gaging stations <br />(A-68, M-34 and C-48) on Apri13`d. The results for these samples are attached. <br />The provisional flow at A-72 on April 3, 2002 was 175 cfs. This flow places the sample <br />result in the intermediate flow category (100cfs<Q<300cfs). The dissolved zinc value for <br />this sample, obtained by averaging the results from two labs, was 707 ugJl. <br />The index number for the April sample is calculated as follows: <br />Xi = 707 <br />Xf= 399 <br />Sf= 144 <br />Ni = (707 - 399) /144 <br />Ni = +2.14 <br />The index number graph and updated reporting table are attached. <br />Evaluation of the normalized data: <br />The index value of +2.14 for April 2002 indicates that the dissolved zinc concentration at <br />the reference point A-72 was significantly above the mean value of the reference data for <br />the intermediate flow class. It appears based on an increased flow over that observed in <br />Apri12001 (175cfs vs 94cfs) that the melt and spring flush effect started early. The <br />dissolved zinc concentrations were comparable (707 ug/I vs 758 ug/1). <br />The 12 period moving average of index values rose to +0.22 from +0.20 because the 707 <br />ug/I is replacing a 758 ug/1 in the 12 month average but the flow classes are different. The <br />12 month average of (+0.22) is below the +0.577 benchmark value in the Consent <br />Decree. <br />