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April 1998 Monthly Report <br /> Page 3 <br /> The index number graph and updated reporting table are attached. <br /> Evaluation of the normalized data: <br /> The index value of +2 .73 for April, 1998 indicates that the <br /> dissolved zinc concentration at the reference point A-72 was <br /> significantly higher than would be expected in comparison to the <br /> mean and standard deviation of a reference data set although it is <br /> comparable to the +2 . 61 obtained in April of 1997 . <br /> The other three mainstem gaging stations were similiar in <br /> concentrations and flow to 1997 with elevated dissolved zinc <br /> concentrations. The Animas was the largest contributor for both <br /> years. Riverwatch data shows this being somewhat typical at A-68 <br /> with 1993 being even higher (1700+ ug/1) and 1995 also elevated <br /> (1000+ ug/1) but not to the same level. <br /> Following is a comparison table of the gaging station results for <br /> April of 1997 and 1998 . <br /> Gaging 1997 Flow 1998 Flow 1997 dZn 1998 dZn <br /> Station cfs cfs ug/l ug/1 <br /> A-72 88 86 843 858 <br /> A-68 25 29 1440 1510 <br /> M-34 34 48 520 510 <br /> C-48 19 13 910 830 <br /> The 12 period moving average of index values for dissolved zinc at <br /> A-72 (graph attached) rose to +0. 607 for April, 1998 as compared to <br /> +0 . 597 for March 1998 . This rise may not prevent the moving <br /> average from dropping to +0.577 or lower if May monitoring results <br /> for dissolved zinc at A-72 are around 700 ug/l. <br />