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~~ process. A 2.8 to 1 horizontal to vertical slope gradient will be maintained during the construction of the tailings dam, which will be raised in successive stages to a maximum height of 30 feet. When the tailings impoundment dam has reached its storage capacity, it will occupy a rectangular area that will have the dimensions 400 feet by 260 feet at its longest and widest points. ~l 1 ~fw(~ ~ IlL'X~LII Yk S~Ura p ~ LLa r m ({tizrz~ A /~ This milling complex has been designed to maintain a stable water balance throughout the ore processing and tailings impoundment system. The milling operation will require 4 tons of water for every ton of ore processed in the gravity and flotation concentration circuits. Fresh water will be intro- duced into the milling process in the grinding circuit (see Figure 11. Most of the water that w. .1 be used in grinding and classification, and in the gravity concentration circuit, will be recycled from the thickener tank overflow launder back to the ball mill. Fresh water will also be added to the thick- ened pulp as it passes from the thickener tanY, underflow to the flotation concentration circuit. A closed circuit has been planned to recycle ~r,~ water that will accompany the tailings pumped from the mill to the tailings retention structure. The excess water that accumulates in the tailings pond will be decanted from the water pool and stored under- ground in the Hazel A. adit. A steel pipe with water decant holey will be used to remove the excess water that collects in the tailings pond. This decantation line will be used to control the water level in the tailings pond, ar~d to keep the water pool as far as possible from the crest of the embank- ment. Additional sections of steel pipe will be connected to the decantation line to regulate the elevation of the water pond as the tailings dam's height is increased. Several seep rings will be attached to the steel pipe to pre~~_nt the tailings from piping along the decantation line. TI••_ decan- tation line ~~ill be connected -with the Hazel A. adit through one of the *_^st holes that were drilled by the U.S. Bureau of Mines. This underground storage area will be used to clarify the decanted water by allowing it to settle prior to recycling the water through the mill. It will also provide additional reservoir capacity for the excess water removed from the tailings pond. The amount of water that will be decanted and stored under- ground in the Hazel A. adit will be primarily determined by the water balance maintained throughout the processing and impoundment system. The water consumed in the milling process and lost in evaporation from the tailings pond is not expected to exceed 20 percent of the water used in the mill. The water consumed in the ore m'_11ing process will mainly: result from water entrapped in the gravity and flotation concentrates and in the unconsolidated tailings. Because of the altitude and limited size of the tailings pond, only a relatively small a:,~:~unt of water is expected to be lost due to evaporation. Recycling the mill water will reduce the amount of fresh water needed in the milling process, and decrease the quantity of water pumped from Left Hand Creek. Because of the hillside location selected for the tailings impoundment structure, water runoff inflow will not be sub- stantial. A drainage diversion ditch will be excavated above the tailings pond to intercept surface water runoff and convey it away from the tailings impoundment area. _ A seepage collection ditch will also be excavated around the downstream perimeter of the tailings embankment dam. The water that collects In this ditch will be conveyed by a pipeline to the Hazel A. adit for underground storage and will be recycled through the milling facility. -15-