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• TAB 17 <br />PROBABLE HYDROLOGIC LONgEOUENLES <br />Ground Water <br />Introduction. This tab contains a discussion of the probable hydrologic consequences of <br />the Toast mining plan on the quality and quantity of surface and ground water for the <br />proposed permit and adjacent areas. The significance of each impact or potential impact <br />was determined. The determination of significance has been made considering the magnitude <br />and extent of the impact of a probable hydrologic consequence on the hydrologic balance, <br />existing eater uses, and the intended postmi ni n9 land use of the area. <br />Ground Water Inflows to Pits and Drawdouns. <br />Introduction. This section describes the methods and results used to determine the <br />probable hydrologic consequences of mining in the Yoas[ mining area to ground water <br />• quantity. In order to make the impact assessments, two different analysis techniques were <br />employed. First, pit inflow volumes were determined on an annual basis using an <br />analytical model developed by GeoTrens based on published work by McWhorter (1982). The <br />second analysis determined annual drawdowns in the adjacent overburden and coal aquifers <br />caused by pit inflows using the Theis equation. Because of the limited use potential and <br />yields from the overburden, 4adge and Wolf Creek coal units, the use of more sophisticated <br />analytical techniques (e.g., digital models) is not warranted. <br />McWhorter Analysis for Calculating Pit Inflows. The following is a discussion of the <br />assumptions and input data used in performing the McWhorter pit inflow analysis. Mining <br />is projected to intercept the wedge overburden, the Wedge coal, the Wedge and erburden <br />(Wolf Creek overburden), and the Wolf Lreek coal. Potentiomet ric surface contours for <br />each unit were drawn on mine plan maps (scale: 1"=400') showing areas to be mined each <br />year of the proposed life-of-mine plan. Using a digitizer, saturated and unsaturated <br />areas for each unit were determined by year. The saturated thicknesses for the Nadge and <br />Wolf Lreek overburden were calculated using contour maps of the top of the wedge and Wolf <br /> Creek coals and potentiome[ric contours for the overburden units. The wedge coal's <br />i maximum saturated thickness ranged from 7.5 to 13.5 feet, while the Wolf Creek coal's <br /> saturated thickness was a consistent 17 feet. Potentiomet ric contours for the Wedge and <br />1 Revised 03/24/95 <br />