1989-10-10_REVISION - M1988112 (12)

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Phase 2 will consist of twa raises to the main embankment • and creation of a single disposal area by deposition of the tailings over the top of the splitter embankment. All embankment construction will be performed using native soils as tfie construction material. The Phase 2 disposal area is shown on Figure C-4. A synthetic liner will be placed beneath the main embankment and the entire tailings disposal area. Liner placement will occur on a prepared foundation consisting of fine-grained native soils which have been compacted to 95 percent maximum Proctor density. The liner material will be a 40-mil very low density polyethylene (VLDPE). VLDPE is a highly flexible and ultraviolet resistant liner material which has demonstrated the ability to accommodate field conditions such as settlement and conform to coarse grained materials without puncture. The liner system has been designed to collect water draining from the tailings and route this water to a downgradient collection pond system. • The liner material beneath the disposal area and main embankment will be covered with a drain layer of relatively coarse-grained native soils to provide a drainage layer for tailings dewatering. This layer will be two feet thick over the entire disposal area. A network of 4, 6, 8 and 10-inch diameter perforated ADS pipe will be placed in the drain layer to facilitate drainage. Tailings deposition will be performed using managed thin-lift deposition. Tailings will be spigotted peripherally around the disposal area to allow free water drainage toward the center adjacent to the splitter embankment in the Phase 1 operations and the center of the disposal area in Phase 2 operations. Two free water pools will be created in Phase 1 while during Phase 2 the two pools will be combined into one pool. D-21