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<br />I <br />TAB ,7 <br />PROBABLE HYDROLOGIC CONSEQUENCES <br />Ground Water <br />tntroducti on. This lab contains a discussion of the probable hydrologte consequences of <br />the Nucla mining plan on the quality and quantity of surface and grou~M water for the <br />proposed permit and adjacent areas. The stgntftcanee of each impact or potential fapact <br />was detsrmi med. The determination of significance has been made considering the impact of <br />a probable hydrologic eonaequence on the quality of the human envf ronmant, existing water <br />uses, aM the intended postmining land use at the area. <br />Cround Mater Inflows to Pita and Orawdowna. <br />Introduction. This section deseri bas the methotls and results used to determine the <br />probable hytlrologie conaequexes of mining in the Nuola East mining area to ground water <br />quantity. In order to oaks the impacC assessments, two different analysis techniques were <br />aaryloyed. First, pit inf7 ow volumes ware determined on an annual basis using an <br />• anal yti sal approach developed by McWhorter, 1962. The aeeond analysis fnvol ved the <br />determination of annual pit inf7 ow rates end annual drawdowns to the adj scent overburden <br />and coal aquifers as a result of the pit inflows. This analysis employed the use of the <br />USCS 3-di nensi anal ft ni te-dlfferance ground water flaw nwdal MODFLOW. <br />The too analysic techniques show a range 1n year 5 pit inflow volumes of from 20.5 to 44 <br />acre feet. This is largely due to the fact that the McWhorter analysis assumes no <br />recharge. It was felt that one anal yaia technique should incorporate the ef(eeta of <br />recharge and thus it was incorporated in the MODFLOM model tuna, All drawdown projections <br />were ce leulateO usfng the higher pit inflow rates that include the effects of recharge. <br />McWhorter Analysis for Calculating Pft Inflows. The fo7lowt m~ fa a di stases on of the <br />asausptions and input data used in performing the McWhorter pit tnflow analysis. The <br />saturated thickness for the overburden wss determined by usfng average yearly water level <br />values frao adjacent noni tors ng walla and a contour map of the top of the Dakota coal. <br />The Dakota coal~a saturated thickness was ealcul atpd by using the average coal seam <br />thf ckneaa per year (Tables 17-1 end 17-2). Values used for hydraulic conductivity, <br />77-1 Revised 04/71/80 <br />u <br />REVISED MARCH 2006 Attachment 2.05.6(3)-2-8 <br />