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towards the pits causing measurable drawdowns in the immediate vicinity of the <br />pits.) Neither model specifically considered shallow aquifer recharge <br />resulting from irrigation, although existing field data from the overburden <br />and coal aquifers include characterizations modified by irrigation <br />conditions. Consequently these analyses may underestimate impacts during the <br />irrigation season. Peabody plans to monitor pit inflows at Nucla East to <br />verify the accuracy of the predictions. <br />Aquifer characteristic parameters were derived from slug test field data. Two <br />to five tests of multiple wells were used to derive geometric means for <br />hydraulic conductivity, storage coefficients and transmissivity. Saturated <br />thickness data was derived from mean annual water level values for the <br />overburden and the average coal seam thickness. Additional assumptions of <br />each model are in Tab 17 of the permit application. <br />The MODFLOW analysis predicted greater inflows, as expected, due to its <br />capability to model recharge. Both models predicted that the majority of the <br />inflow would be derived from the overburden, and that inflows would be at <br />their highest level during the fifth year of mining (Table 1). The McWhorter <br />analysis predicted 22.1 acre-feet/year (0.03 cfs) of total inflow in year 5 <br />while the MODFLOW analysis predicted 47.1 acre-feet/year (0.06 cfs) of total <br />inflow in year 5. MODFLOW predicted 5' to 30' drawdowns of the overburden <br />aquifer in the pit over the five year period accompanied by 5.8' to 8' <br />drawdowns of the coal aquifer in the pit over the five year period (Table 2). <br />The most extensive drawdown of the overburden aquifer was predicted to occur <br />during year 5 when 2' of drawdown would be observed 0.7 mile from the center <br />of the Nucla East area. By year 5, 0.25' of drawdown could be expected in the <br />coal aquifer 2500' from the center of the permit area. <br />The operator predicts that drawdown may impact water levels found in two of <br />the more shallow, adjacent wells registered in the Nucla area under well <br />permit numbers 97552 and 13592. These wells are 150 feet and 116 feet deep <br />respectively. Impacts will be restricted to nominal increases in the amount <br />of energy required to pump the well, and probably will not be detectable. <br />Table 1 <br />Comparison of Predictions for Mine Pit Inflows <br />from Two Models (acre-feet/year) <br />Year - Model <br />McWhorter MODFLOW <br />ver ur en oa ota ver u en oa o a <br />I 1.21 0.51 1.72 7.36 3.18 10.54 <br />II 1.48 0.47 1.95 7.30 2.29 9.59 <br />III 3.99 0.80 4.79 11.71 2.39 14.10 <br />IV 9.05 1.22 10.27 21.98 2.87 24.85 <br />V 20.5 1.58 22.08 43.90 3.16 47.06 <br />-18- <br />