2008-04-15_REVISION - M1980244 (256)

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~,~ SMITH WILLIAMS CONSULTANTS, INC. • soiUliner interface shear strength than smooth LLDPE geomembrane. Discussions regarding the shear strengths used in the stability analyses are presented in Section 5.1.2.2. Laboratory testing on representative samples of the SLF from the clay borrow indicates that the material will provide an acceptable permeability of 1 x 10-6 cm/s or less when- compacted to 95 percent of standard Proctor maximum dry density at 3% above the optimum water content or 2% below the optimum water content. Other borrow areas maybe identified during operations for use in future construction. A series of liner load tests conducted by Golder (2005) indicate that the liner systems of the VLF can withstand ore depths of approximately 800 feet. Liner load tests were conducted on both ore storage and PSSA liner system configurations from Phase I, Phase II, and Phase IV to assess the geomembrane performance under very high loads. -For the ore storage areas, the liner system consisted of (from the top to bottom) DCF, geomembrane, and SLF; the PSSA liner system consisted of DCF, geomembrane, and LVSCF.. The SLF was placed and compacted to the project specifications to replicate the field conditions. Once the liner system was constructed, a steel platen and hydraulic.ram were used to incrementally load the liner system to between 630 and 670 pounds per square inch (psi) to simulate loading under 800 feet of ore. The tests included holding the maximum load for a minimum of 24 hours before the liner system was unloaded and inspected. After testing, the geomembrane liner was removed and inspected for damage. The results from the testing program showed that all of the VLF liner systems will perform under 800 feet of ore. These results are presented-in Appendix B. For the Phase 5 VLF design, the ore depth for the Phase I through IV VLF is proposed to be increased to 800 feet over the liner system, while the ore in Phase 5 will be stacked to 590 feet. It is important to note that increasing the ore height to 800 feet primarily affects the ore loading on the ore storage area, within the VLF. The additional ore height has only a minor affect. on the ore loads within the existing PSSAs. The VLF area that will have ore stacked over 590 feet is less than 20% of the entire VLF lined area. The area of the VLF with ore stacked at 800 feet is less than 5% of the total VLF. In addition, the average ore height over the liner for the ultimate VLF is less than 350 feet. Figure-3 presents the ore depth isopach for the VLF. Based on this layout, the ore loads within the existing PSSAs change less than 10 percent; the average ore height in the Phase I PSSA is 420 feet, the average ore height in the Phase II PSSA is 220 feet, and the average ore height in the Phase IV PSSA is 440 feet. S:\PROJECTS\1125 CCBV PHASE 5 VLF\H2 - DESIGNWREQUA VLF\VLF PHASE 5 FINAL REPORT V2.DOC 24