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<br />Animas above Silverton. A68 <br />Remediation of combined mine waste and either the phase 1 or phase 2 adit scenarios <br />will have very little effect on reducing the concentration of Al, Cd, Cu, Fe, Mn, or Zn at <br />A68. Cd and Mn will continue to exceed chronic TVS under the average stream flow <br />condition in the late winter and early spring. Zn will continue to exceed both acute and <br />chronic TVS year-a-round. Cu, when corrected for the dissolved fraction, should meet <br />TVS. AI and Fe meet aquatic life TVS criteria. <br />A substantial amount of Cd, Mn, and Zn enters the Animas River from unidentified, <br />diffuse sources between Arrastra Gulch and Abb. The largest tailings piles (previously <br />ponds} in the Basin lie near the river along this- stretch. The site is permitted and has <br />undergone extensive remediation work over the past ten years. In the fall of 1999, a <br />trench was dug to bedrock above the tailings, and a barrier and drainage system was <br />installed to capture groundwater flow that might enter the piles. Data collected after <br />1999 was not used for the UAA Therefore, the impacts of the most recent remediation <br />work are unknown. In addition, it is doubtful that one year's data would be enough to <br />identify changes in water quality due to these actions. Given the minimal remediation <br />potential identified upstream, an evaluation of the "reversibility" of the load of Cd, Mn, <br />and Zn that -enters the Animas River between Arrastra Gulch and A68 will be needed to <br />determine if water quality can be substarrtially improved at A68. This is currently under <br />investigation (1VPS 319 Segment 3a Characterization Project). <br />Cement Creek at Silverton. CC48 <br />Remediation of combined mine waste and the phase 1 adit scenario should reduce <br />levels of Cd, Cu, and Zn belov~~ levels encountered in Cement Creek before SGC began <br />treatment of upper Cement Creek at the Gladstone treatment plant. implementation of <br />the phase 2 scenario in Cement Creek will have only a small beneficial effect beyond <br />phase 1 on the concentration of Cd, Cu, and Zn at CC48, unless phase 1 is significantly <br />unsuccessful. Figures 11.1 d and 11.1 a indicate that either the phase 1 or phase 2 <br />remediation scenario will have little effect on levels of Fe or Mn. Remediation will have <br />no effect on the level of Al. Concentrations of all six metals will remain above both <br />acute and chronic TVS for aquatic life. Metal reductions will benefit downstream <br />segments of the Animas River however. <br />Mineral Creek near Silverton. M34 <br />Remediation of combined mine waste and the phase 1 adit scenario should reduce <br />levels of Cd, Cu, and Zn to concentrations that meet chronic TVS during average stream <br />flow. The current level of Mn is less than TVS for aquatic life. Implementation of phase <br />1 reductions should Lower the level of total recoverable Fe, however it will continue to <br />exceed aquatic life TVS year-a-round. This analysis shows that remediation is nat <br />expected to measurably change the concentration of dissolved recoverable Al, which will <br />continue to exceed acute TVS criterion during the winter. Implementation of phase 2 <br />reductions will primarily lower levels of total recoverable Fe, however, Fe will continue <br />to be higher than TVS for aquatic life. <br />