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• 2. Length in water (feet) is the same as the total length of the cuts for each year. <br />3. Time in water is the result of dividing the length in water for a given year by the <br />pit advancement per day for the same year. This value represents the number of days <br />the pit will be open and subject to pit inflow each year. <br />4. Pit advancement is the constant length in feet per day that the pit will advance for <br />the year. It is calculated by dividing the total area to be mined in a given year by <br />a constant pit width. Pit width varied for each year. <br />5. Geometric mean values for transmissivity and hydraulic conductivity were used based <br />on aquifer tests, while liberal estimates were used for storativity values. <br />6. The saturated thickness for each aquifer is based on average water level monitoring <br />values that are representative of the area to be mined. <br />7. QNATURAL is the amount of aquifer through flow which will be intercepted by each <br />years pit advancement in gallons. <br />8, ODRAINAGE is the linear portion of inflow from aquifer storage in gallons. <br />9, OTOTAL is the sum of QNATURAL and QDRAINACE for a given year in gallons. <br /> As can be seen in Tables 17-1 and 17-2, the lowest pit inflow for the Wadge Coal (combined <br />• areas) will occur in 1994, The h ighest Wadge Coal pit inflow will occur in 2001. For the <br /> overburden aquifer, the lowest pit inflow will occu r in 1997; the 1997 mine area is <br /> unsaturated, so no pit inflows are expected. As with the Wadge Coal, the highest <br /> overburden pit inflow will occur in 2001. <br />Drawdowns from Pit Pumpage and Extent of Water Level Declines. The following analyses <br />will show a worst case drawdown situation for each aquifer by artifically determining <br />pumpa ge rates so that highwall drawdowns will not exceed aquifer saturated thicknesses <br />before the end of a given time period. For this exercise, one-foot and five-foot drawdown <br />radii will be used to determine the extent of water level declines as a result of pit <br />pumpa ge. <br />Several assumptions must be made to estimate ground water inflow into the pit and the <br />extent of drawdowns. These are as follows: <br />1. Pit inflows are simulated by a single pumping well with a one-foot radius, and a <br />. theoretical pumpage rate can be predicted by use of the Theis non-equilibrium well <br />formula. <br />• 2. No recharge to the aquifer is considered (worst case scenario). <br />3. The radius of influence is defined as the radius of the cone of depression where the <br />piezometric head has decreased by one or five feet. <br />9 <br />