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r1 <br />LJ <br />Mining into the saturated coal bed will produce mine inflows as the coal bed is <br />dewatered. Experience gained by mining in the graben indicates initial flow rates will be <br />much greater than the flow rate after mining. Using Darcy=s law to calculate the flow <br />rate in the graben after mining yields the following: q =kia = (0.11) (4,500 x 8) (0.05) _ <br />198 cubic feet per day = 1.02 gpm. Where area is the length times height of <br />development 4500 feet times 8 feet and the hydraulic gradient is the slope of the coal <br />seam 5%. This calculation checks favorably with the estimated flow rate presented <br />above. <br />The February 18, 1985, Hydro-Geo Consultants report speculates the source of water <br />for the mine are surface streams and/or shallow aquifers from the upper reaches of <br />McClane Creek. This would indicate the flow though the coal seam is from the <br />northwest to the northeast. Therefore, long term flow into the mine will enter from the <br />exposed northwest coal ribs and the water should percolate into the downdip northeast <br />exposed coal ribs. The top or maximum elevation of the saturated coal zone is <br />projected at about 5580 feet. The elevation of the floor of the mine portals is about <br />5610 feet over 30 feet above the saturated coal zone. Since the hydraulic gradient of <br />the saturated coal zone is below the elevation of the portals, perpetual mine discharge <br />is improbable. The coal at the portal would be saturated if the hydraulic gradient within <br />the mine plan area were high enough to cause perpetual mine discharge. There is no <br />compelling evidence (drill holes are all dry) that would indicate the mine workings will <br />intersect any substantial perched aquifer system that would alter the hydrologic <br />characteristics in the mine plan area. <br />The rate at which the saturated coal ribs are exposed should govern the maximum mine <br />inflow rate. A five entry system exposes 1,480 lineal feet of rib per 100 feet of advance <br />assuming 80 foot square pillars. That same 100 feet of development produces 5,400 <br />tons of coal assuming an eight foot mining height. Based upon the k factor of 0.11 feet <br />per day, it takes about one year to dewater an 80 foot square pillar (40 feet / 0.11 feet <br />per day). Therefore, exposed coal ribs contribute to mine inflow for one year. At an <br />annual production rate of 0.5 million tons per year, using this five entry system, a total <br />of 9,000 feet of development would be required. This would expose 133,000 <br />[(1,480)(9,000)/100] feet of rib. This amount of exposed rib would produce an <br />estimated maximum mine inflow as follows q =kia = (0.11) (133,000 x 8) (0.05) = 5,900 <br />cubic feet per day . 30 gpm. A production rate of 1.7 million tons per year would <br />increase the projected water flow to about 100 gpm. The most recent mine inflow <br />calculation for 2005 was 31.4 gpm (2005 AHR) which is in the same order of magnitude <br />as that calculated for the 0.5 million ton per year production rate. <br />Some of the mine inflow may be consumed underground during normal operations. <br />However, during periods of downtime, all of the mine inflow will be pumped to the <br />surface and discharged into East Salt Creek. For the purposes of projecting the effect <br />• mine discharge will have on East Salt Creek, it will be assumed the maximum mine flow <br />Appendix N - TR-16 - 2 - 10/08 <br />