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When the Times Mine bulkhead was constructed in the summer of 1987, Gold Hill Ventures, <br /> Ltd., was the operator of the Cash Mine and the Gold Hill Mill. The bulkhead was designed by <br /> Louis W. Cope, P. E., an independent Colorado Registered Professional Engineer and Gold Hill <br /> Ventures, Ltd. retained consultant. It was constructed by two very competent, experienced <br /> underground miners who knew what they were building. Practically every Mining Engineers' <br /> Handbook ever published in the last hundred years contains a section on constructing <br /> underground bulkheads to control or retain water. A review of the literature available at that time <br /> discloses that the US Bureau of Mines considered a single three foot thick concrete bulkhead to <br /> be more than adequate for this purpose. CMC believes that the Times Mine bulkhead can <br /> withstand the maximum hydrostatic pressure for the amount of process water that will be stored <br /> behind the bulkhead. The Times Mine bulkhead is three (3) feet thick. At the location of the <br /> bulkhead in this narrow point in the Cross-cut, the bulkhead is six (6) feet high and four (4) feet <br /> wide. What follows is a calculation for the fluid pressure on the bulkhead: <br /> Maximum Fluid Pressure: <br /> P=D x H D=Water Density 62.4 lbs. /ft3 & H=fluid height in ft. <br /> P=62.4x6' <br /> P=374.4 lbs./ft2 or 2.6psi when divided by 144 in2 per ft2 <br /> Pressure on bulkhead(using pressure at base, for whole bulkhead 6'x 4' or 3,456 in2) <br /> P=2.6 psi x 3,456 in2 =8,985.6 lbs. on bulkhead total height <br /> This would be the maximum load for no more than 6 feet of water for a width of 4 feet where the <br /> bulkhead is situated in the Times Mine Cross cut. <br /> Note: The load would decrease with height, such that the pressure at the bottom of the bulkhead is 2.6 psi, <br /> while at the top the pressure approaches 0 psi. Since the input pipe is 4.5 feet above the floor,the centroid <br /> would be 2.25 feet above the floor of the mine, or 2.25 feet below the water surface. <br /> This is believed to be the maximum pressure that could be present behind the Times Mine bulkhead,with <br /> the Cross-cut completely full of water, and it is not more than the bulkhead can safely handle. <br /> 12) What is the maximum elevation at which the operation proposes to store water in the Winona <br /> Mine workings versus the elevation of the Times Mine portal, and the collar elevation of the 50 <br /> foot winze that connects the Times Mine to the Wynona Mine? Will the operation need to keep <br /> water levels below a particular elevation to minimize hydrostatic pressure on the bulkhead? How <br /> does the operation intend to monitor water levels in the workings (e.g.,pressure transducer with <br /> data logger, periodic manual measurements)? <br /> 7 <br />