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the values for the two areas into the above equation yields a total recharge rate from the spoil areas of about <br />170,000 gpd (23,000 ft3 /day) or 190 acre -ft per year (see following calculation). An additional 200 gpm (320 <br />acre -ft per year) will come from the 6 -Right area. Since this area is higher than most of the mine workings, it is <br />expected to flow at that rate for most of the time the mine is refilling. Thus, the total average recharge rate after <br />mining is expected to be approximately 510 acre -ft per year. <br />Q = ((7.5 ft2 /day * 300 ft * 5,000 ft) /1,000 ft) + _ ((7.5 f2 /day * 300 ft * 15,000 ft)/ 3,000 ft) <br />Q = 23,000 ft3 /day = 170,000 gpd = 190 acre - ft/year <br />The Wadge overburden unit in mined areas is estimated to consist of a rubblized zone about 100 (t,) feet thick <br />and an overlying highly fractured zone about 200 feet thick (t2). The area of the Wadge Seam mining operations <br />is about 24 square miles (13,100 acres) (A,). Outside of the mined area, the overburden unit will have <br />reasonably similar characteristics to baseline conditions. This area is approximately 6 square miles (3,840 <br />acres) (AA For this relatively simple calculation, the following parameters are estimated: <br />Average drawdown in mined areas <br />= 1,000 feet (d,) <br />Average drawdown in unmined areas <br />= 500 feet (d2) <br />Porosity of rubblized zone <br />= 0.1 (p,) <br />Porosity of highly fractured zone <br />= 0.01 (p2) <br />Confined storage coefficient (all zones) <br />= 0.0001 (S) <br />The total volume of water required to restore potentiometric levels to pre- mining conditions is given by: <br />V = A, {t,PI + t2p2 + S (d, - (t, + t2))) + A2 Sd2 <br />where: V = total volume of water (acre -ft) <br />A, = area dewatered (acres) <br />A2 = area of potentiometric lowering but no dewatering (acres) <br />t, = thickness of rubblized zone(ft) <br />p, = porosity of rubblized zone <br />t2 = thickness of highly fractured zone (ft) <br />P2 = porosity of highly fractured zone <br />S = confined storage coefficient (all zones) <br />d, = average drawdown in dewatered areas (ft) <br />d2 = average drawdown in non - dewatered areas (ft) <br />Substituting the assumed values in this equation yields a value for V of 158,100 acre -ft (see following <br />calculation). Using a recharge rate of about 510 acre -ft per year, it can be seen that it would take about 310 <br />years (158,100 acre -ft/510 acre -ft/yr) for the overburden unit to recover to premining levels. <br />V = (13,100 acre * ((100 ft * 0.1) + (200 ft * 0.01) + (0.0001 * (1000 ft — (100 ft + 200 ft)))) + 3,840 <br />acre * 0.0001 * 500 ft) <br />V = 158,100 acre -ft <br />Assuming that the enhanced permeability of the rubblized zone and highly fractured zone above the Wolf Creek <br />Seam results in a hydraulic connection between the Wadge and Wolf Creek seams, the additional time required <br />to fill the volume encompassing the Wolf Creek Seam and Wadge /Wolf Creek Interburden affected by mining <br />can be calculated by the same method. The area encompassed by the mine (A,) is 4,688 acres, and the average <br />thickness of the interburden is 167 feet. The rubblized zone (t,) would comprise the lower 100 ft of interburden, <br />and highly fractured zone 02) would comprise the remaining 67 feet of interburden. Mining of the Wolf Creek <br />Seam is not expected to significantly increase the area or degree of dewatering area above the Wadge Seam or <br />the surrounding area experiencing drawdown. Consequently, A2, d, and d2 are zero, and the equation becomes: <br />V = A, {t,p, + t2p2) <br />TR13 -83 2.05 -141 11/03/14 <br />