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4. There is currently no clear evidence that mine water is communicating with the <br />alluvial fill Pad at locations other than in the vicinity of Sump 10, but further study is <br />needed. In order to conduct such study, the alluvial fill must be substantially <br />dewatered, the creek diversion pipeline must be in place, and solid source term <br />materials within the alluvial fill must have been excavated in accordance with <br />cleanup criteria as proposed in Attachment 1. <br />The schedule to initiate additional physical investigation of potential migration of mine <br />pool water is tied to remediation of source term materials within the Pad, currently <br />scheduled for late summer or fall of 2012 in accordance with the diversion pipeline and <br />associated Pad dewatering schedule. <br />Three potential remedial strategies to address potential impacts to water quality in <br />Ralston Creek and Ralston Reservoir from the mine pool are discussed below: <br />1. mine dewatering and ex -situ water treatment; <br />2. in -situ treatment of mine pool water to reduce source concentrations; and <br />3. grouting to permanently seal potential conduits for migration. <br />These remedial strategies each have advantages and disadvantages in terms of potential <br />effectiveness, sustainability, secondary environmental consequences, and major <br />implications with respect to the amount of time required to achieve permanent protection <br />of water quality in Ralston Creek and successfully reclaim the Site. A detailed <br />comparative analysis of remedial strategies for the mine pool was provided to DRMS in <br />response to the agency's December 14, 2010 adequacy review of the Environmental <br />Protection Plan. That assessment is provided as Attachment 2 to this submittal. <br />With respect to a schedule, in -situ treatment could be implemented quickly (within a <br />matter of months). In -situ treatment is expected to rapidly reduce concentrations of <br />uranium and other metals in the mine pool. This would greatly reduce or even eliminate <br />the potential for measurable impacts to shallow alluvial groundwater or Ralston Creek as <br />a result of any migration of mine pool water. <br />Grouting of potential conduits for migration of mine water would be a passive and <br />possibly permanent solution; however, potential conduits could not be detected unless the <br />hydraulic head of the mine pool remains above that of the alluvial fill. In addition, <br />grouting would require that the diversion pipeline is in place to dewater the alluvial fill <br />and protect the creek in the interim, and the alluvial fill must have been excavated in <br />order to expose potential indications of mine pool migration. Although a grouting <br />program could conceivably commence in the summer /fall of 2012, completion of such a <br />program is unlikely prior to the summer /fall of 2014 as an appropriate period of <br />monitoring would be required to verify success. <br />Mine dewatering and ex -situ treatment could not be initiated for at least two years <br />because a large (3+ acre) evaporation and sludge retention pond would need to be built, <br />5 <br />