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TAB 17 PROBABLE HYDROLOGIC CONSEWENCES Ground Water Introduction. This Tab contains a discussion of the probable hydrologic consequences of the Seneca II-W mining plan on the quality and quantity of surface and ground water for the proposed permit and adjacent areas. The significance of each impact or potential impact was determined. The determination of significance has been made considering the impact of a probable hydrologic consequence on the quality of the human environment, existing water uses, and the intended pos training land use of the area. C round Water Inflows to Pits and Drawdowns. Introduction. This section describes the methods and results used to determine the probable hydrologic consequences of mining in the Seneca II-W mining area to ground water • quantity. In order to make the impact assessments, two different analysis techniques were employed. First, pit inflow volumes were determined on an annual basis using an analytical approach developed by McWhorter (1982). The second analysis determined annual d rawdowns in the adjacent overburden and coal aquifers due to pit inflows using the Theis equation. It should be noted at this point that due to low Overburden and Wadge Coal hydraulic conductivities, only small inflows will occur and the use of more sophisticated analytical techniques (e.g., digital models) is not warranted. McWhorter Analysis for Calculating Pit Inflows. The following is a discussion of the assumptions and input data used in performing the McWhorter pit inflow analysis. Mining is projected to intercept both the overburden and Wadge Coal aquifers. Poten ti ometric surface contours for each aquifer were drawn on mine plan maps (scale: 1"=400') showing areas to be mined each year. Since the north and south mining areas have different hydrologic properties, these areas were analyzed separately. Using a digitizer, saturated and unsaturated areas for each aquifer were determined by year. The saturated thickness for the overburden was calculated using a contour map of the top of the Wadge Coal and potentiometric contours for the overburden aquifer. The Wadge Coal's saturated thickness was set at the average coal seam thickness of 12 feet, rvhich is relatively consistent for the area. Potentiometric contours for the Wadge Coal were used to determine the pressure head above this confined aquifer. 1