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~I` ?a <br />'~. <br />SMITH WILLIAMS CONSULTANTS, INC. <br />• <br />slopes of 2H:1 V, as explained in Section 4.4. The Phase 5 VLF ore topography is shown on <br />Drawing A200, and cross sections through the VLF are shown on Drawing A210. <br />The majority of pregnant solution generated during operation of Phase 5 VLF will be contained <br />within the Phase 5 VLF internal PSSA. Where the Phase 5 ore overlaps onto Phase IV, the <br />pregnant solutions will report to the Phase I and II PSSAs. The Phase 5 PSSA will be <br />constructed on native ground and compacted fill and ore, and is located along the eastern edge of <br />Phase IV. The western edge of the PSSA will be founded on the regraded and compacted Phase <br />IV ore slope. The eastern edge of the PSSA will be founded on compacted fill overlying either <br />native ground (Squaw Mountain) or the regraded Arequa Gulch Overburden Storage Area <br />(AGOSA). The PSSA embankment and termination berms will be constructed from compacted <br />fill. <br />The majority of the ore storage area will be constructed on native ground and compacted fill <br />overlying bedrock, with the exception of the northeastern edge of the ore storage area, which will <br />be constructed on the regraded slopes of the AGOSA. <br />As part of the Phase 5 VLF design, a dynamic water balance model was developed to determine <br />• the volume of solution that would be generated as a result of the additional Phase 5 VLF area. <br />The dynamic water balance model tracks solution through the ore heap and reporting to the <br />PSSAs. The model incorporates delays in solution movement through the ore heap and time- <br />dependant draindown. As in previous Amendments, the water balance model accounts for <br />normal operating volume, solution accumulation due to seasonal climatic variations to a 95- <br />percent confidence interval, 12-hour draindown during pump outages, and excess water during <br />extreme climatic conditions (100-year/24-hour storm event), while maintaining the minimum <br />freeboard within each PSSA. The minimum freeboard for the Phase 5 PSSA is 5 feet. <br />Operational and post closure surface-water diversion systems have been designed around the <br />perimeter of the VLF. The operational Phase 5 VLF diversion channel will need to be <br />constructed along the margins of the VLF. During the construction and operation of the Phase 5 <br />VLF, temporary surface-water diversion channels also will need to be constructed to route <br />surface-water flow away from disturbed areas, as needed. The post closure surface-water <br />diversions would be located along the margins of the reclaimed VLF slopes. Permanent surface- <br />water diversion channels have been designed to divert upgradient surface water generated from <br />the 100-year/24-hour storm event. In addition, a sedimentation pond has been incorporated into <br />the design. The sediment pond is located along the north end of the Phase 5 VLF and was <br />designed to fully contain two times the run-off from the 10-year, 24-hour storm event applied to <br />S:\PROJECTS\1125 CCBV PHASE 5 VLF\H2 - DESIGNWREQUA VLFlVLF PHASE 5 FINAL REPORT V2.DOC '7 <br />