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V = A3 {tlp1 + t2p2) <br />Thus, the calculated volume, VwcR, to refill the dewatered zone between the Wolf Creek Reserve and the <br />overlying Wadge Seam is: <br />VWCR - (4,688 acre * ((100 ft * 0.1) + (67 tt * 0.01) <br />VWCR — 50,020 acre-ft <br />and the additional time required to refill the dewatered zone between the Wolf Creek Reserve and the overlying <br />Wadge Seam is about 100 years (50,020 acre -ft/510 acre- ft/yr). <br />Discharge from the unit will start to occur once gradients toward discharge areas are re- established. This may <br />occur before premining potentiometric levels are achieved. Discharge from the unit will Iengthen the time <br />required to restore premining potentiometric levels. <br />Drawdown in the Trout Creek Sandstone will occur if communication is established with mine workings <br />through fault zones. As previously discussed, this is not expected to occur. To date, no measurable impact to <br />the Trout Creek Sandstone has been observed. Impacts to existing wells in the Trout Creek Sandstone should be <br />minimal since these wells are all located at the margins of the Twentymile Park Basin, as shown on Map 15, <br />Alluvial Valley Floors and Water Rights. In the unlikely event that drawdown effects do occur, they are not <br />likely to extend to these areas, given the average recharge rate to the unit calculated at approximately 70 gpm <br />and the storage within the unit calculated at about 360,000 acre -ft (refer to Section 2.04.7). TC has located all <br />active adjudicated Trout Creek Sandstone wells within the affected area. TC will determine if monitoring water <br />levels in these wells is necessary, as TC is the owner of the TCSs wells shown on Map 15. <br />Diminution of Bedrock Discharee to Alluvium and Surface Streams <br />Ground water inflows from bedrock units to the underground mine will cause drawdown of potentiometric <br />levels in these units and changes in the direction of ground water flow. This may result in a decrease of natural <br />ground water discharge to alluvium and surface streams. This effect may persist long after mining ceases since <br />it may take an appreciable amount of time for potentiometric levels to recover to premining conditions. <br />The Wadge and Wolf Creek overburden/interburden units are the most likely to be affected by the ongoing and <br />proposed mining operations; however, the extremely low permeability of the Wadge /Wolf Creek <br />Interburden and Wolf Creek Coal Seam, and the very limited hydraulic connection with overlying units is <br />expected to limit any significant effects from these units. The Twentymile Sandstone is not expected to yield <br />significant inflows to the mine and therefore, no diminution of natural discharge is anticipated. The Trout Creek <br />Sandstone is not expected to be substantially affected by the mining. <br />The Wadge overburden unit has been calculated to discharge approximately 11,000 gpd (12.3 acre- ft/yr.) under <br />premining conditions. The dewatering and potentiometric lowering that will occur in this unit during mining <br />will probably result in most of this discharge being eliminated. During mining, this will be more than offset by <br />direct discharge of mine inflow water to Fish and Foidel Creeks. Much of this water is derived from storage in <br />the unit and considerable extra storage will be created by the mining operation. Consequently, once mining <br />ceases, it will take many years for potentiometric levels to recover. It has been calculated in the previous <br />section that it may take about 410 years before potentiometric levels are re- established to premining conditions. <br />Discharge from the unit may start to occur prior to total re- establishment of potentiometric levels, but this will <br />be minimal until the old mine workings are flooded to at least the elevation of the discharge area at around 6,600 <br />feet. At least 90 percent of the mine workings are below this elevation. Consequently, it is assumed for "worst <br />case" predictions, that the mining operation will cause a diminution of bedrock discharge from the Wadge <br />overburden and Wadge /Wolf Creek interburden units of about 11,500 gpd, equivalent to 0.02 cfs, for at least <br />PR14 -10 2.05 -141.1 12 /18 /14 <br />