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<br />2010 <br /> <br />. <br /> <br />Figure 5 near here. <br /> <br />The primary cause of elevated metal concentrations in the upper A.xansas River is acidic. metal-laden <br /> <br />drainage from abandoned mines and mine tailings. The most substantial sources of mine drainage are located in the <br /> <br />Leadville area and include the Leadville Mine Drainage Tunnel (LMDT) and the Yak Tunnel (Moran and Wentz. <br /> <br />1974; Wentz. 1974; Bunting. 1989; Clements, 1991), although nonpoint sources of mine drainage in the Leadville <br /> <br />area are undoubtedly significant as well. The LMDT discharges to the East Fork of the A.xaJ1sas River upstream <br /> <br />from Leadville and the Yak Tunnel discharges to California Gulch near Leadville. In the spring of 1992, water- <br /> <br />treatment plants came on line at both sites. Both plants utilize a chemical-precipitation procedure to remove metals <br /> <br />from the mine drainage before being discharged to receiving streams.As previously mentioned. treatment plants <br /> <br />were installed at the two most substantial sources of mine drainage. the LMDT and the Yak Tunnel, in the spring <br /> <br />of 1992. This action coincided with the last year of data collection for the study. The pre-treatment (April 1990- <br /> <br />. Man:h 1992) and post-treaDlent (April 1992-March 1993) dissolved and total-recoverable metal data were <br /> <br />compared for statistical differences with the Wilcoxon rank-sum test. The results of this analysis are presented in <br /> <br />Table 2. The statistical test results indicate that concentrations of Cd, Cu, Mn. and Zn were significantly smaller (p <br /> <br />< .05) during the post-treament period at many sites between Leadville and Parkdale, therefore. the occurence of <br /> <br />metal concentrations exceeding aquatic-life water-quality standards has also decreased in the post-treatment <br /> <br />period. One complicating factor in the analysis is that streamflow was typically larger for the post-treatment <br /> <br />samples than for the pre-treatment samples. although the difference in instantaneous streamflows for the 2 periods <br /> <br />was not stntistically significant at any site. Statistical testing on flow-adjusted concentrations was not perfonned <br /> <br />because of the absence of any significant explanatory variables for metal concentrations. Although. these test <br /> <br />. <br /> <br />11 <br />