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Mr. Tom Kaldenbach <br />April 5, 2013 <br />Page 5 <br />containment of water in the mine pool should be monitored over an extended period of time <br />before the containment can be considered a success. <br />Cotter will continue to monitor and report mine pool level and water quality at the same intervals <br />and using the same methods currently in practice at the mine. These analyses will be reported to <br />DRMS for a period of ten years in conjunction with the quarterly report requested in Item 17 <br />below, beginning after the second quarter of 2013. <br />10. Please add a firm commitment in Exhibit E stating that, in the event In -Situ treatment fails to <br />adequately achieve remedial performance benchmarks, Cotter will conduct mine dewatering and <br />ex -situ treatment to a depth of 150 feet, or other depth as necessary, to maintain a clear hydraulic <br />gradient into the mine and protect Ralston Creek from potential impacts related to the mine pool. <br />In the event in -situ treatment results, as described in Cotter's response to comment 26 below, <br />cannot be sustained, Cotter firmly commits to taking the necessary actions required to ensure <br />negative impacts to Ralston Creek are mitigated. <br />11. Please add to Exhibit E a conceptual design for a perpetual, passive ex -situ treatment system <br />and identf the specific criteria which must be met by the water quality in the mine pool and <br />Ralston Creek before passive ex -situ treatment will begin. <br />Cotter believes that uranium concentrations in the mine pool, consistent with those presented in <br />the response to comment 26 below, are reasonably obtainable and therefore passive ex -situ <br />treatment will not be required. Thus, Cotter is not proposing a passive treatment system at this <br />time. However, should such a need be identified in the future, Cotter will propose to DRMS a <br />system appropriate to the site conditions and consistent with state and federal permit requirements <br />at that time. <br />12. Please add to Exhibit E an option to make the diversion pipeline a permanent structure, and <br />specify the criteria that must be met for making the decision to leave it as permanent, and the <br />criteria that must be met before removing the pipeline. <br />Cotter discussed with Federal regulatory agencies the idea of a permanent pipeline when the <br />creek by -pass was being explored in late -2010. Those discussions highlighted important issues <br />associated with a permanent diversion pipeline, e.g., permanent loss of riparian and Preble's <br />Meadow Jumping Mouse habitat. Any attempt to permit a permanent pipeline would likely be <br />met with significant opposition. It is Cotter's belief that the solid source material mitigation <br />proposed in AM -04, coupled with mine -pool mitigation via in -situ treatment, will be <br />accomplished within the 10 -year permit of the existing pipeline. The absence of solid source <br />material in the valley between the mine and Ralston Creek and in -situ results in the mine pool <br />consistent with those detailed in the response to comment 26 below will justify removal of the <br />temporary diversion pipeline. <br />13. Please identify in Exhibit E the treatment concentration targets for uranium and other <br />constituents of concern. <br />Please see Cotter's response to comment 26 below. Additionally, concentration targets for site - <br />specific constituents of concern will take into account the results of the newly installed monitor <br />wells, which will help define background water quality. <br />