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Ground Water Inflow to the Mine <br />• The underground mining activities at the Foidel Creek Mine will result in reduction of the original hydrostatic <br />pressure within the Wadge Coal Seam to atmospheric conditions. Bedrock units overlying and underlying the <br />Wadge Coal Seam will be under higher hydrostatic conditions and consequently, if there is sufficient hydrologic <br />communication, there will be movement of ground water from these units into the active mine workings. <br />The overburden unit will be directly affected by the removal of the Wadge Coal Seam. Good hydrologic <br />communication with the unit may occur through natural fractures and faults, which are enhanced by stress-relief, <br />and subsidence related to the mining activity. Complete dewatering of the immediately overlying overburden unit <br />by gravity drainage is anticipated in active mine areas. Lateral movement of ground water in the overburden unit <br />toward the active mine areas will cause some dewatering and more general lowering of potentiometric levels near <br />the mine. <br />Historic Inflows: The Foidel Creek Mine has been operated since 1983. Since that, time inflows and discharges <br />have been monitored. In addition, a number of estimations of future inflows have been prepared. Past inflow, <br />estimates have been made using theoretical models. Since more than 4000 acres of area have now been mined, the <br />most recent inflow estimates have been made using historic inflow to project future inflows. <br />The quantity of mine inflow and the resultant effects on potentiometric levels on the Wadge overburden unit were <br />studied using atwo-dimensional finite-difference, simulation model for the original Foidel Creek Mine permit <br />application (Exhibit 13, Ground Water Model Documentation). The results and predictions of the model were <br />used in the development of a Mine Water Control Plan included in Exhibit 33. Most of the estimated infow was <br />projected to occur as leakage from the Trout Creek Sandstone through faults intersecting the mine. Additionally, <br />the projected inflows projected for the existing mining operation have not been realized to date. This is based <br />upon the fact that it was anticipated that the faults would act as conduits and allow for Flow of ground water into <br />~,he mine. The mine has not intercepted the number of faults originally projected and, in addition, the faults have <br />been dry. <br />To date, June 1999, none of the faults identified in this report has yielded sustained inflows. >n addition, no <br />evidence has been found that there is any significant connection between the mine workings and either the <br />underlying Trout Creek Sandstone or [he overlying Twentymile Sandstone. One significant localized inflow was <br />encountered in the 6-Right Entry in late 1997. <br />The discussion of the historic inflows are divided by mining areas: I) the North Mains and portal areas (NMS), 2) <br />The I" Panel South plus the South West panels (Panels ]SW to 3 SW) plus the South Panels (1 Left to 6 Left) <br />which will be called the Western Mining District (WMD) 3) the Eastern Mining Dis[ric[ (EMD) consisting of <br />Panels 2Right to 9 Right, and 4) the Northern Mining District (NMD) consisting of Panels 12 Right through 16 <br />Right.. Future mining areas are the rmaining panels in the Northem Mining District (NMD) and the Northwest <br />Mining District (NWMD) containing the reserves to the north and west of the WMD. The current areas listed in 1 <br />through 4 are shown on Map 16. <br />InFlows have historically been encountered in the NMS area. From 1993 to 1997 the inflows to the NMS, as <br />measured in the annual mine infow surveys remained constant at approximately 30 to 40 gpm. The conductivity <br />of this water, which ranges from approximately 2500 to 4500 µmhos/cm, indicates that it is primarily derived from <br />groundwater that has been mixed with spoil water from the updip spoils. Atypical spoil well analysis is shown in <br />Exhibit 49, Table E49-1. It has a mixed cation - sulfate bicarbonate water with a conductivity of 3610 µmhos/cm. <br />U addition, most of this inflow has been observed from seeps that are within 2000 feet of the portal. <br />n <br />U <br />APPROVED JUN 2 8 2000 <br />PR 99-OS 2.05-135 03/28/00 <br />