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r~ <br />u <br />lhopwed HP( MoNromg Pion far rhs Ncw Harimn Mine ? <br />The drinking water standazd (for pId7 was also violated at well GW-N20. <br />Agricultural standards #azled in 2 wells, GW-N7A (Dakota coal) and GW-N22 (alluvial} At <br />well GW-N22, the manganese standard was also violated. Wells located in the Dakota Coal <br />strata are not generally considered suitable for a potable water source. <br />Probable Hydrologic Consequence <br />A discussion of the probable hydrologic wnsequcnces and reclamation plan are contained <br />in Section 205.6(3) and Section 205.6(3)(b)(v) of the permit application document. The <br />following discussion is intended to supplement the description of potential impacts of mining <br />and mitigation of these potential effects. The determination of significance has been made <br />considering the impact on the quality of the human environment, esisting water uses, and <br />the intended post mining land use of the area. <br />Interruption of groundwater flow and drawdown. In ordei to develop the impact assessment <br />for groundwater quantity, two different analyses techniques were ut0ized. Fus; pit inflow <br />volumes were determined on an annual basis using an analytical approach developed by <br />• McWhorter, 1982 The second analysis involved the determination of annual pit inflow rates <br />and annual drawdowns in the adjacent overburden and wal aquifers as a result of the pit <br />inflows. This analysis utilized the USGS 3-dimensional Suite-difference groundwater flow <br />model MODFLOW. <br />Traosieat simulations were performed for afive-year period, using the matdmum drawdown <br />estimates for the overburden and coal. For the overburden, the pit drawdown was S feet <br />for years 1 and 2, 8 feet during year 3, 15 feet during yeaz 4, and 30 feet during yeaz 5. The <br />overburden drawdown wntoun do not intersect any of the boundaries, therefore, no impact <br />of the San Miguel River from drawdown in the deeper part of the overburden is predicted. <br />Shallow aquifer flow inm Tuttle and Calamity Draws in the vicinity of the pit will be <br />decreased, but will be offset by pumpage from the pit. The drawdown for the coal <br />simulation was 8 feet during yeaz 1, 5.8 feet doting yeaz 2, 6 feet during year 3, 73 feet <br />during yeaz 4, and 8 feet during year 5. Some boundary effects aze evident on the coal <br />drawdown plots as the drawdawn eventually intercepted all four boundaries, including the <br />San Miguel River. Simulated average dally pit inflow for the coal and overburden aquifers <br />varied from 1,755 cubic feet per day in yeaz 1 to 5,604 cubic feet per day in yeaz S. WFCs <br />approach to these potential impacts iS to monitor the aquifers avid discharge from the pit <br />to determine the eMent of drawdownJ The monitotng program proposed in the following <br />section of this document should provide rcasonabty accurate measurements of effects of <br />mining. Should the proposed monitoring show that impacts to the groundwater aquifers are <br />preluding its use, WFC will provide alternate water sources of compazable quantity and <br />quality. As described in the water augmentation plan, WFC has a 114 acre foot consumptive <br />• <br />Attachment 2.04.7-5-33 <br />