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July 1998 Monthly Report <br /> Page 3 <br /> - Mainstem Stream Monitoring and Reference Point Stream <br /> Monitoring <br /> Sunnyside sampled the reference point (A-72) on July 1, 1998 <br /> and the three mainstem gaging stations (A68, M34 and C48) were <br /> sampled by the Bureau of Reclamation. The sample results for <br /> Sunnyside's A-72 reference point sample are attached. <br /> The provisional flow at A-72 was 945 cfs which places this <br /> sample result in the high flow category (Q> 300 cfs) . The <br /> dissolved zinc value for this sample obtained by averaging the <br /> results from two labs was 220 ug/l. <br /> The index number for the July sample is calculated as follows: <br /> Xi= 220 <br /> Xc= 306 <br /> Sf= 104 <br /> Ni= (Xi - Xf)/Sf <br /> Ni= (220 - 306)/104 <br /> Ni= -0. 83 <br /> The index number graph and updated reporting table are attached. <br /> Evaluation of the normalized data: <br /> The index value of -0.83 for July, 1998 indicates that the <br /> dissolved zinc concentration at the reference point A-72 was <br /> significantly lower than the mean value of the data for the high <br /> flow class. In comparison to the July 9, 1997 sample result, the <br /> 220 ug/l is an improvement of 10 percent. In comparison to the <br /> June 10, 1998 sample, there was a slight improvement (220 ug/l <br /> verses 232 ug/1) between June loth and July 1st although the <br /> results are basicly the same with a 73% increase in flow. <br /> Since the index value is less than +2 . 0, Sunnyside does not plan <br /> any additional monitoring or re-analysis. <br /> The 12 period moving average of index values for dissolved zinc at <br /> A-72 (graph attached) dropped to +0. 345 in July. This is a <br /> continuation of the downward trend observed since December, 1997. <br />