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August 1999 Monthly Report <br /> Page 4 <br /> The index number for the August sample is calculated as follows: <br /> Xi = 237 <br /> Xf= 306 <br /> Sf= 104 <br /> Ni = (Xi—Xf) /Sf <br /> Ni = (237— 306) /104 <br /> Ni = -0.66 <br /> The index number graph and updated reporting table are attached. <br /> Evaluation of the normalized data: <br /> The index value of -0.66 for August, 1999 indicates that the dissolved zinc concentration <br /> at 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 August 5, 1998 sample result, this <br /> value is lower (237 ug/l verses 290 ug/1). The flows were (584 cfs verses 291 cfs). The <br /> August 5, 1998 sample has a better comparison to the reference data set (-0.76 verses <br /> —0.66) because it is in the intermediate flow class. <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 rose to +0.59 from +0.58 even though it <br /> was significantly lower than the reference data set because the result it was replacing was <br /> even lower. While this value is still above the+0.577 benchmark value in the Consent <br /> Decree, it appears that the abnormally high value in May was not part of a continuous <br /> monthly pattern. It will require monitoring results significantly lower than the reference <br /> data, in order for the 12 month average to drop and stay below+0.577 before November <br /> or December. <br />