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July 1999 Monthly Report <br /> Page 4 <br /> The provisional flow at A-72 on July 6, 1999 was 757 cfs which places this sample result <br /> in the high flow category (Q>300cfs). The dissolved zinc value for this sample, obtained <br /> by averaging the results from two labs, was 180 ug/l. <br /> The index number for the July sample is calculated as follows: <br /> Xi = 180 <br /> Xf= 306 <br /> Sf= 104 <br /> Ni = (Xi—Xf) /Sf <br /> Ni = (180 — 306) /104 <br /> Ni = -1.21 <br /> The index number graph and updated reporting table are attached. <br /> Evaluation of the normalized data: <br /> The index value of -1.21 for July, 1999 indicates that the dissolved zinc concentration at <br /> the reference point A-72 was significantly lower than the mean value of the reference <br /> data for the high flow class. In comparison to the July 1, 1999 sample result, this value is <br /> lower (180 ug/1 verses 220 ug/1) with a lower flow(757 cfs verses 945 cfs). <br /> Since the results are significantly lower than the reference data set and the immediately <br /> previous years monitoring results, Sunnyside does not plan any additional monitoring. <br /> The 12 period moving average of index values dropped to +0.58 from+0.61. While this <br /> value is still above the +0.577 benchmark value in the Consent Decree, it appears that the <br /> abnormally high value in May was not part of a continuous monthly pattern. It will <br /> require monitoring results significantly lower than the reference data, in order for the 12 <br /> month average to drop and stay below+0.577 before November or December. <br />