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What can be provided in support of the expectation that ground water flow from the Grassy <br />• Valley area would report to the diatreme is the information relative to the hydraulics of the <br />rock: <br />1. The Grassy Valley diatremal rock is derived from the Grassy Valley volcanic feeder <br />(MLE Project Application, Appendix 1, Figure 9). This volcanic feeder was emplaced at the <br />same time as, and apparently from the same source as, the other feeders in the diatremal <br />system. Thus, there is no basis to believe that the geology and hydrogeology of volcanic <br />material in the feeder is any different than the geology and hydrogeology that exists in the <br />remainder of the diatremal rock. This indicates that if there is an outlet for the water from the <br />Grassy Valley feeder to the portion of the diatreme that eventually migrates to the regional <br />ground water table that is intersected the Carlton Tunnel (i.e. the south feeder) then the <br />diatremal rocks would be expected to have sufficient hydraulic conductivity to allow drainage. <br />2. There is a strong head gradient vertically downward from the surficial deposits in <br />Grassy Valley to and within the diatremal rock beneath. This is illustrated by nests of water <br />monitor wells drilled in the diatreme in Grassy Valley, within the footprint of the proposed <br />ECOSA (location shown as West Well Nest on Figure 1 included as Attachment 8). The <br />results of these wells are summarized in Table 1 below: <br />Table 1- Water Levels beneath ECOSA <br /> <br /> Ground Top of Bottom of Depth Water <br />Well Surface Open Open to Level <br />Name Elevation Interval Interval Water Elevation <br /> (ft msl) (ft bgs) (ft bgs) (ft msl) (ft msl) <br />OSABH-4 10179 18 38 21 10158 <br />CAM-1 B 10174 50 70 56 10118 <br />CAM-1A 10174 130 200 165 10009 <br />These data show that there is a strong downward vertical gradient in the material beneath the <br />ECOSA footprint. The diatremal materials can be partially saturated almost from the surface, <br />but the water pressure in the formation down to 200 feet below ground surface is only slightly <br />above atmospheric. These are conditions of strong gravitational flows from the colluvium <br />through the diatreme, and are consistent with infiltrated water proceeding down through the <br />diatreme. <br />The elevation of the lowest monitoring well (CAM-1A) in the diatreme is approximately 250 <br />feet above the lowest point of potential flozty to Grassy Creek (at approximately the elevation of <br />9,750 ft). CC&V is currently conducting field activities to complete an additional ground <br />water monitoring well nest at greater depths in order to provide that demonstration. These <br />well nests, both with completions at approximately 25, 50, 200, 450, and 700 feet below <br />ground surface are expected to provide direct evidence of downward flow in the footprint of <br />the diatreme in this area, which is the same as the flow regime that exists in all other areas of <br />the diatreme. <br />• 3. The Cameron Mine extends from an elevation of 10,200 to an elevation o <br />.? of <br />approximately 9,200 ft (MLE Project Application, Appendix 6, Figure 4). This fits within the <br />24