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Potential impacts to the hydrologic balance and the likelihood that these impacts will occur are <br />given below. <br />1) Containment of pit inflow and impacts on water quality. All runoff and pit pumpage from <br />disturbed areas will be routed through approved NPDES sedimentation pond(s). These pond(s) <br />will be designed and constructed to impound runoff and pit pumpage from areas disturbed by <br />mining and provide sufficient residence time to insure that the pond discharge water chemistry <br />meets the effluent requirements specified in the NPDES Permit. A reviewof the chemical and flow <br />data indicates that the potential for any discharge from any NPDES pond to exceed receiving <br />stream or federal standards is minimal. Past history of mine operations at the Nucla Mine indicate <br />very few exceedances of the standards over the years of operations. <br />2) Interruption of groundwater flow and drawdown In order to develop the impact assessment <br />for groundwater quantity, two different analyses techniques were utilized. First, pit inflow volumes <br />were determined on an annual basis using an analytical approach developed by McWhorter, 1982. <br />The second analysis involved the determination of annual pit inflow rates and annual drawdowns <br />in the adjacent overburden and coal aquifers as a result of the pit inflows. This analysis utilized the <br />USGS 3- dimensional finite - difference groundwater flow model MODFLOW. <br />Transient simulations were performed for a five -year period, using the maximum drawdown <br />estimates for the overburden and coal. These drawdown results are expressed as a maximum at <br />the pit and are expressed as a conical depression which results in decreased drawdown at further <br />distance from the mine. For the overburden, the pit drawdown was 5 feet for years 1 and 2, 8 feet <br />during year 3, 15 feet during year 4, and 30 feet during year 5. The drawdown for the coal <br />simulation was 8 feet during year 1, 5.8 feet during year 2, 6 feet during year 3, 7.3 feet during year <br />4, and 8 feet during year 5. The zero impact contour for the overburden and coal after five years <br />of mining is approximately 4,000 feet. The overburden and coal drawdown contours do not <br />intersect any of the boundaries, therefore, no impact of the San Miguel River from drawdown in the <br />deeper part of the overburden or coal is predicted. Shallow aquifer flow into Tuttle and Calamity <br />Draws in the vicinity of the pit will be decreased, but will be offset by pumpage from the pit. <br />Simulated average daily pit inflow for the coal and overburden aquifers varied from 1,255 cubic feet <br />per day in year 1 to 5,604 cubic feet per day in year 5. WFC's approach to these potential impacts <br />is to monitor the aquifers and discharge from the pit to determine the extent of drawdown. The <br />hydrological monitoring program should provide reasonably accurate measurements of effects of <br />mining. Should the monitoring show that impacts to the groundwater aquifers are precluding its <br />use, WFC will provide alternate water sources of comparable quantity and quality. As described <br />Revised August 2010 (PR06) 2.05.6(3) -20 <br />