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May 1997 Monthly Report <br /> Page 4 <br /> The reported dissolved zinc value is 605 ug/l which is the <br /> average of results from two labs and of repeat analysis by <br /> these two labs. <br /> Repeat analysis were requested because the average of the <br /> reported values resulted in an index value of 2.95. Under the <br /> terms of the Consent Decree agreement, observations with an <br /> index value greater than +2 will be reanalyzed. <br /> The index number for the May sample using an average of the four <br /> results is calculated as follows: <br /> Xi = 605 <br /> Xf = 306 <br /> Sf = 104 <br /> Ni = (Xi-Xf)/Sf <br /> Ni = (605-306)/104 <br /> Ni = 2 . 88 <br /> The index number graph and updated reporting table are attached. <br /> n, Evaluation of the normalized data: <br /> 7' The index value of 2 . 88 for May indicates this result was <br /> significantly higher her than the mean value of the reference data for <br /> the high flow class. Since the initial index value of 2 .95 was <br /> more than +2 , each lab reanalyzed the sample for dissolved zinc <br /> resulting in a recalculated index value of 2 .88 . <br /> BOR's sample results for May 7, 1997 , dissolved zinc concentration <br /> c , at A-68 was 680 owI741 ; M-34 was 370 j41; and C-48 was 980 wmj74� <br /> v Attached is a table and graph of the calculated index values. <br /> Also, since May is the 12th month since A-72 monitoring was started <br /> V)by Sunnyside, a 12 period moving average graph of the index values <br /> is attached. Since both of the last 2 out of 3 index values have <br /> been greater than +2 and the 12 month moving average was greater <br /> d\ethan +0.577 (+0.947) , Sunnyside submits the following evaluation to <br /> satisfy section A. 3 (d) of the Consent Decree. <br /> 1) Which subbasin is experiencing the increase; <br /> Sunnyside' s A-72 monitoring data shows little variance from <br /> the reference data set for June, 1996 through November, 1996. <br /> From December, 1996 through May, 1997 significant increases <br /> from the reference data set have been observed although only <br /> April and May have exceeded a +2 index value (ie, 2 standard <br /> deviations above the reference data mean for the respective <br /> flow class) . <br />