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GROUND WATER - SENECA II-W SOUTH AREA Introduction This Tab addresses the probable hydrologic consequences (PHCs) from the Seneca II-W South area mining expansion, and includes the Wadge, Sage Creek and Wolf Creek coal seams. Issues of concern include potential impacts to the quality and quantity of ground water and surface water in the proposed mine area and adjacent areas. The significance of each potential impact has been determined considering the local environment, ecosystemisl, existing water uses, and the intended post-mining land use of the area. Monitoring locations included in the ground water sampling program are included in Exhibit 7-1, Hydrologic Monitoring Map. Water Inflows to Pits and Drawdowns Introduction This section describes the methods and results utilized to determine potential impacts to ground water quantity in the Seneca II-W South area. The hydrogeologic assessment required the use of two analytical techniques: 11 pit inflow volumes determined on an annual basis using Darcy's Law; and 21 annual drawdowns in the adjacent overburden and coal aquifers due to pit inflows determined using the Theis equation (Freeze and Cherry, 19791. Due to low hydraulic conductivity estimates for the Wadge, Sage Creek and Wolf Creek overburden and coal aquifers, small volumetric discharge into the pit excavations is expected and, therefore, the use of more sophisticated analytical techniques le.g., digital computer models) is not warranted. Darcy Analysis for Calculating Pit Inflows The following is a discussion of the pit inflow analysis for the Seneca II-W South expansion area. Mining in the Seneca II-W South area is projected to intercept portions of the Wadge, Sage Creek and Wolf Creek overburden and coal aquifers. Potentiometric surface maps of the Wadge Overburden and Wadge Coal water-bearing units are shown in Drawings 7-2A, Potentiometric Surface Map, Wadge Overburden Aquifer, and 7-3A, Potentiometric Surface Map, Wadge Coal Aquifer, respectively. Average 1997 ground water level elevations at each well site were utilized to generate the two Wadge maps. The saturated thickness of the Wadge overburden, required for the pit-inflow analysis, was calculated to be 24 feet using water-level data and the lithologic log from wells WOV4-1 and WOV4-2, the monitoring wells completed in Wadge overburden within the Seneca II-W South area. The boreholes logs and well cross- reference table is included in Table 7-2. The saturated thickness value used for the Wadge coal aquifer was assumed to be equal to the average coal seam thickness 112 feet), which is relatively consistent for the Seneca II-W and Seneca II-W South areas (see Tab 6-11• Potentiometric surfaces of the Sage Creek and Wolf Creek coal units are shown on Drawings 7- 36, Potentiometric Surface Map, Sage Creek Coal and 7-4A, Potentiometric Surface Map, Wolf Creek Coal. As indicated in the original permit, the coal units are confined ground water systems. The potentiometric surfaces were estimated using the top of coal surface. The coal 86 Revised 1/02