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The Phase 5 Extension of the VLF will result in a larger footprint to the pad as <br />well as a maximum heap height (above the liner) of up to 800 feet. The liner <br />system of the expansion area is consistent with the liner systems used in the rest <br />of the VLF. Composite liners are used throughout and a leak detection system <br />plus another geomembrane layer is included under the pregnant solution storage <br />area (PSSA). Other aspects of the design, including the maximum foundation and <br />heap side slopes are consistent with previous designs. The results of the stability <br />analyses show that the heap slopes will be stable under static and pseudo-static <br />loading conditions. <br />A significant part of this review focused on the high heap height. Three specific <br />issues of interest are: <br />• Liner puncture resistance under the high normal stresses of the 800 feet <br />high heap; <br />• Behavior of leachate collection pipe system under high normal stresses; <br />and <br />• Behavior of the heap leach ore under high normal stresses to ensure <br />adequate pore space for leachate collection. <br />The current permitted height of the VLF is 590 feet and no liner puncturing has <br />been detected, i.e. no large scale leaks that effect the water balance are present <br />and no cyanide solutions have been detected in the leak detection piping system <br />installed underneath the composite liner system. The Ore Depth Isopach map is <br />presented in Figure 3 of the AMEC report. Note that only about 18 percent of the <br />VLF area will have a final height above the presently permitted height of 590 <br />feet. <br />The design calls for the installation of an 80 mil LLDPE as part of the composite <br />liner system and 100 mil LLDPE as part of the liner system in the PSSA. The <br />three issues above are discussed in the following subsections. <br />a. Liner Puncture Resistance <br />The evaluation of the 800 feet height included a series of laboratory <br />puncturing tests performed in preparation of the last two Phases of the <br />VLF. These tests were performed by the Golder Associates, Inc. laboratory <br />in Lakewood and specific care was taken to test thin lifts of drain <br />materials overlying the geomembrane and a layer of compacted clay. <br />Testing thin lifts of drain material prevent arching from developing during <br />the test. Details of these tests are described in Appendix B.2 of the AMEC <br />report. After the loading test the geomembrane sample was subjected to <br />a vacuum test to 77 mm Hg was done to identify any pinholes as a result <br />of liner puncturing. <br />3