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<br />process. A 2.8 to 1 horiz6ntal to vertical slope gradient <br />will be maintained during the construction of the tailings <br />dam, which will be raised in successive stages to a maximum <br />height of 30 feet. When the tailings impoundment dam has <br />reached its storage capacity, it will occupy a rectangular <br />area that will have the dimensions 400 feet by 260 feet at its <br />longest and widest points. <br />This milling complex has been designed to maintain a stable <br />water balance throughout the ore processing and tailings <br />impoundment system. The milling operation will require 4 tons <br />of water for every ton of ore processed in the gravity and <br />flotation concentration circuits. Fresh water will be intro- <br />duced into the milling process in the grinding circuit (see _ <br />Figure 1). Most of the water that will be used in < <br />classification, and in the gravity concentration c: <br />be recycled from the thickener tank overflow laun <br />the ball mill. Fresh water will also be added tc <br />etted pulp as it passes from the thickener tank u <br />the flotation concentration circuit. A closed <br />been planned to recycle the water that will ac <br />tailings pumped from the mill to the tailing: <br />structure. The excess water that accumulates in t <br />pond will be decanted from the water pool and st <br />ground in the Hazel A. adit. A steel pipe with N <br />holes will be used to remove the excess water that <br />the tailings pond. This decantation line will <br />control the water level in the tailings pond, and <br />water pool as far as possible from the crest of <br />ment. Additional sections of steel pipe will be c <br />the decantation line to regulate the elevation o: <br />pond as the tailings dam's height is increased. ~ _ __ <br />rings will be attached to the steel pipe to prevent the <br />tailings from piping along the decantation line. The decan- <br />tation line will be connected with the Hazel A. adit through ~' <br />one of the test holes that were drilled by the U.S. Bureau of <br />Mines. This underground storage area will be used to clarify <br />the decanted water by allowing it to settle prior to recycling j <br />the water through the mill. It will also provide additional <br />reservoir capacity for the excess water removed from the <br />tailings pond. <br />The amount of water that will be decanted and stored under- <br />ground in the Hazel A. adit will be primarily determined by <br />the water balance maintained throughout the processing and <br />impoundment system. The water consumed in the milling process <br />and lost in evaporation from the tailings pond is not expected <br />to exceed 20 percent of the water used in the mill. The water <br />consumed in the ore milling process will mainly result from <br />water entrapped in the gravity and flotation concentrates and <br />in the unconsolidated tailings. Because of the altitude and <br />limited size of the tailings pond, only a relatively small <br />amount of water is expected to be lost due to evaporation. <br />Recycling the mill water will reduce the amount of fresh water <br />needed in the milling process, and decrease the quantity of <br />water pumped from Left Hand Creek. 1 <br />Because of the hillside location selected for the tailings• I ~+ <br />impoundment structure, water runoff inflow will not be sub- ~ <br />stantial. A drainage diversion ditch will be excavated above <br />the tailings pond to intercept surface water runoff and convey. i <br />"``it away from the tailings impoundment area. "~~,: ~ <br />.-- <br />A seepage collection ditch will also be excavated around the <br />downstream perimeter of the tailings embankment dam. The <br />water that collects in this ditch will be conveyed by a <br />pipeline to the Hazel A. adit for underground storage and will <br />be recycled through the milling facility. <br />-15- <br />