1997-05-29_REPORT - M1977378 - Laserfiche WebLink

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April 1997 Monthly Report Page 4 - Mainstem Stream Monitoring and Reference Point Stream Monitoring Sunnyside sampled the reference point (A-72) and the other three mainstem gaging stations (A-68, C-48 and M-34) on April 11, 1997. These results are on the attached summary sheets. The provisional flow from the outside gage at A-72 for the April 11, 1997 sample was 93 cfs which is in the low flow category (Q < 100 cfs) . The reported dissolved zinc value is 843 ug/l which is the average of results from two labs and of repeat analysis by these two labs. Repeat analysis were requested because the average of the reported values resulted in an index value of 2.47. Under the terms of the Consent Decree agreement, observations with an index value greater than +2 will be reanalyzed. The index number for the April sample using an average of the four results is calculated as follows: Xi = 843 Xf = 519 Sf = 124 Ni = (Xi-Xf)/Sf Ni = (843-519)/124 Ni = 2.61 The index number graph and updated reporting table are attached. Evaluation of the normalized data: The index value of 2.61 for April indicates this result was significantly higher than the mean value for the reference data for the low flow class. Since this result was more than +2, each lab reanalyzed the sample for dissolved zinc. These results were slightly higher. Based on Sunnyside's sample results for April 11, 1997, dissolved zinc concentrations at A-68 was 1440 ug/l, M-34 was 520 ug/1 and C-48 was 910 ug/l. These results would indicate that all three sub-basins were carrying elevated zinc concentrations on April 11, 1997. It appears that zinc concentrations in these sub- basins were elevated (based on Sunnyside's data from August 1996 - February 1997) by the following percentages; Cement Creek 20%, Mineral Creek 20% and Upper Animas 120%.