2011-03-14_REVISION - M1977493 (65)

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CM0001760 Page 6 the Dam's riprap face, as well as bentonite amendment of the borrow material to meet the permeability requirement for Zone 1. Geotechnical testing classified the Mosquito Fault borrow material as a clayey sand with a permeability that would make the material suitable for construction of the Zone 1 impervious core without addition of bentonite. Use of the Mosquito Fault borrow material is based on evaluations of both the material's hauling costs (i.e., the Mosquito Fault is west of Highway 91 on the Climax Mine) and chemical composition. The cost benefit of using Mosquito Fault soil over bentonite-amended soil is discussed in Section 4.4. The chemical characteristics of Mosquito Fault soil is being evaluated by CMC and is beyond the scope of this report. 4.1.2 Quantity Available Figure 4 shows the development of the Tenmile Tunnel Portal, the East Island and the West Island borrow areas. The development was based on soil depths from the test pits logs, borehole logs and physical constraints (e.g., haul roads, underground pump station pipeline alignment). Appendix B contains the `Borrow Soil Quantity Calculation Brief which describes the development procedures and estimated available borrow material quantity calculation. Table 4 summarizes the quantity calculation results of both the quantity of materials required to construct each zone of the Dam, as well as borrow area materials available from each borrow source. Material quantity estimates, discussed in sections 4.4 through 4.8 , indicate that approximately 101,000 CY of materials are required to construct the Dam. Of this quantity, approximately 10,000 cy is riprap which is assumed to be available from exposed fractured bedrock areas not included in the available borrow area material quantity calculations. Quantity calculations of available borrow material indicate that approximately 104,000 cy of Dam soil construction materials are readily available as follows: the Tenmile Tunnel Portal Borrow Area is estimated to yield approximately 41,500 cubic yards (cy) of soil after unusable material (e.g., peat) is removed; accounting for elevation differences between the topographic map and the test pit location surveys, the West Island Borrow Area is estimated to yield approximately 9,200 cy; and the East Island Borrow Area is estimated to yield approximately 29,800 cy. For the remaining Dam construction materials, it was conservatively assumed that approximately 50 percent (i.e., 30,000 cy) of the material from the Dam's foundation excavation volume, c:V7ynnlrypmsWimu'no1dunk6104rep2.doc I1R)1N6 _ .. ? =Environmental