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Mr. Michael C. Refer <br /> CAMAS America, Inc. / <br /> 12 September 1994 <br /> Page <br /> approx' acre-feet, for 500 ac-ft storage. Note that Sectio <br /> annexation agreement s to be less than or non to minimize <br /> evaporative losses. The ratio cannot be rage volume at this time because <br /> active storage will be a functio erformed by the Town in the <br /> future. Figure - Mining Plan, for the State it No. 4 to be <br /> ex on and shows the configuration of the proposed Pe ite <br /> at the completion of mining. <br /> HYDROGEOLOGY <br /> Haley & Aldrich's earlier interpretation of the reservoir site hydrogeology included the occurrence of <br /> a continuous water table surface beneath the site occurring as fracture flow in low permeability <br /> bedrock consisting of granitic gneiss and granite. During late June and early July of this year, <br /> additional geotechnical investigations were performed that provided new hydrogeological information <br /> and which substantially confirmed our earlier interpretation of ground water conditions at the site. <br /> Specifically, four deep core holes were drilled, additional ground water level observations were made, <br /> bedrock hydraulic conductivity tests were performed, and additional geologic mapping was done in <br /> the Central Quarry area. The details of these investigations will be presented in both the MIM <br /> permit amendment package that is currently being prepared and in a data report to Cooley for <br /> inclusion in its annual report to the State due in December 1994. Conclusions from this work are <br /> included herein as they relate to the issue of potential seepage losses from the reservoir. <br /> Of the four core holes drilled, two were drilled from the floor and two were drilled on benches on the <br /> west and south sides of the Central Quarry . The water level observations in these holes together <br /> with observations of ground water seepage and ponding associated with excavation of a new bench <br /> level below the earlier pit floor elevation of approximately 6500 ft are consistent with the <br /> interpretation of a water table beneath the pit floor between El 6480 and El 6470 and dipping to the <br /> north. This water table has already been depressed by recent mining activities, but should be <br /> reestablished by the filling of the reservoir. This hydrogeologic condition is, in Haley & Aldrich's <br /> opinion, favorable with respect to potential reservoir seepage losses and should result in tolerable <br /> seepage losses from a pool elevation at or below approximately El 6475. <br /> Packer tests were performed in the core holes to measure bedrock permeability. These test results for <br /> rock beyond the blast halo surrounding the pit varied from approximately 5 x 101 cm/sec to zero take <br /> (no measured permeability). Our best engineering judgement at this time is that the rock mass has an <br /> average permeability of 1 x 10's cm/sec or less except for localized higher permeability in fractured <br /> zones that comprise a small (10 to 20 percent) portion of the overall rock mass. Our earlier seepage <br /> loss assessment assumed a range of 1 x 10'to 1 x 101 cm/sec for permeability. The new data <br /> suggest that this was a reasonable estimated range and that the permeability of the rock is probably <br /> closer to the middle to lower end of the range. This refinement of Haley & Aldrich's anticipated <br /> permeability further suggests that seepage losses from the reservoir will be manageable. <br /> K�A <br />