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n <br />U <br /> <br />The drinking :w,ittr standard lfur pH) was uiso •noimed at well GW-V _tl. <br />.~¢ricultural standard, failed in'_ wells. GW"-~~0 (Dakota troal) and GW-Y~? (alluvial). Ae <br />well GW-Y~^. [he manganese standard was also violated. Wells located in the Dakota Coal <br />sttata are not generally considered suitable for a potable water sourrx. <br />Probable Hydrologic Consequence <br />A discussion of the probable hydmlogic cottsequezxcs and reclamation plan are con[ained <br />in Section 2.OS.6(3) and Section ?.05.6(3)(b)(v) of the permit application documen[. The <br />following discussion is intended to supplement the description of potential impacts of mining <br />and mitigation of these potential etTecss. The determination of significance haz been trade <br />considering the impact on [he quality of the human environment existing water uses, and <br />the intended-post mining land use of the azea. <br />lnterru~don of sroundwater flow and drawdown. [n order to develop [he impact assessment <br />for groundwater quantity, two diffe[eat analyses techniques were utilized Firs; pit inflow <br />' volumes were determined on an annual basis using an analytical approach developed by <br />• McWhotter,1982. The second analysis involved the determination of annual pit inflow rates <br />and annual drawdowns in the adjacent overburden and coal aquifers as a result of the pit <br />inflows. This analysis uttlized the USGS i-dimensional finitedifference groundwater flow <br />model MODFLOW. <br />Transient simulations were performed [or n five-year period, using the maximum drawdown <br />estimates for the overburden and coal These dmwdown results are expressed as a <br />maximum at the pit and are expressed as a conical depression which results in decreased <br />dmwdown az further distance from the mine. For the overburden, the pit drawdown was <br />S feet for years ]and ? 8 Feet during year i. 15 feet during year 4, and i0 feet during year <br />S. The drawdown for the coal simularion was 3 feet during year I, S.3 feet during year 2, <br />6 feet during year 3, 7.3 fee[ during year •F, and 3 feet during year 5. The zero impact <br />contour for the overburden and coal after five years of mining is approximately ~t.G00 feet. <br />The overburden and coat drawdown contours do not intersect any of the boundaries, <br />therefore, no impact of the San Miguel River From drawdown in the deeper pnrt of the <br />overburden or coat is predicted. Shallow aquifer flaw hem Tuttle and Calamity Dtaws in the <br />vicinity of the pi[ Wall bt decreased. but will be offset by pumpage Pram the pit. Simulated <br />avernge daily pit inflow for the coal and overburden aquifers varied from 1.2SS cubic feet <br />per day in year 1 [0 5,604 cubic Feet per day in year :. WFC's approach to these potential <br />impacts is to monitor the aquifers and discharge from the pit to determine the extent of <br />dravMOwa The monitoring program in the following section of this document should <br />provide reasonably accurate measurements of effects of mining. Shuuld the monitoring show <br />that impacu to the groundwater aquifers are precluding its use. WFC will provide alternate <br />l0 <br />• <br />Attachment 2.04.7-5-13 <br />