1999-07-26_HYDROLOGY - M1977378 - Laserfiche WebLink

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May 1999 Monthly Report Page 4 Ni = (Xi—Xc) / Sf Ni = (211 — 306) / 104 Ni = -0.91 The index number graph and updated reporting table are attached. Evaluation of the normalized data: The index value of+4.26 for May, 1999 indicates that the dissolved zinc concentration at the reference point A-72 was significantly higher than the mean value of the reference data for the intermediate flow class. In comparison to the May 7, 1998 sample result, the 1013 ug/1 is significantly higher (1013 ug/l verses 553 ug/1) but the flow was only 44% of what it was in 1998 (125 cfs verses 284 cfs) although both results are in the intermediate flow category. Although the index value is greater than +2.0, Sunnyside did not request a lab reanalysis, because the sample was originally split and sent to two different labs for analysis. These results were comparable and Sunnyside is confident they are reliable. Since the results were received just prior to Sunnyside's scheduled June sample date, Sunnyside requested an expedited analysis from the labs for the June samples (A-72, A- 68, M-34 and C-48)to determine whether the result was anomalous and if not which tributary was the source. The dissolved zinc values obtained were as follows: A-72 (211 ug/1); A-68 (270 ug/l); M-34 (83 ug/1); C-48 (623 ug/1). these values are relatively low. Therefore, it is not likely that a reason for the abnormally high May dissolved zinc result at A-72 will be found in 1999. Based on the results from the Bureau of Reclamation's (BOR's) mainstem sampling for May 6, 1999 the Upper Animas (A-68) was apparently the major contributor with a dissolved zinc concentration of 1900 ug/l which had dropped to 211 ug/1 by June 9, 1999. The conditions existing on May 6, 1999 were as follows; • The samples were taken on a clear-mild day after a significant wet snowstorm the previous day. The original sample day coordinated with BOR was on May 5"' but it was delayed till May 6°i due to the storm.