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May 1998 Monthly Report <br /> Page 3 <br /> The index number for the May sample is calculated as follows: <br /> Xi= 553 <br /> Xc= 399 <br /> Sf= 144 <br /> Ni= (Xi - Xf)/Sf <br /> Ni= (553 - 399)/144 <br /> Ni= +1. 07 <br /> The index number graph and updated reporting table are attached. <br /> Evaluation of the normalized data: <br /> The index value of +1. 07 for May, 1998 indicates that the dissolved <br /> zinc concentration at the reference point A-72 was higher than the <br /> mean value of the data for the intermediate flow class. In <br /> comparison to the May 5, 1997 sample result, the 553 ug/1 is an <br /> improvement of 9 percent even though it is in a lower flow class <br /> (intermediate flow verses high flow) where concentrations are <br /> normally higher. In comparison to the April 8 , 1998 sample, it is <br /> a significant improvement (553 ug/1 verses 858 ug/1) although it is <br /> in a higher flow class (intermediate verses low) where an <br /> improvement would be expected. It appears that the "spring flush" <br /> period may not have occurred over an extended period of time as it <br /> did in 1997 . <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 +0.456 in May. This is the first <br /> period since the moving average has been calculated that it has <br /> been below the +0. 577 trigger point value in the Consent Decree <br /> that indicated monitoring data at A-72 is statistically different <br /> (ie. worse) than the data in the reference data set. <br /> If you have any questions on this report, please contact me. <br />