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unit to be affected within the proposed permit and adjacent areas are owned by TC. The extent of effects is <br />discussed quantitatively under Mule 2.05.6(3)(b)(iii), Probable Hydrologic Consequences. <br />Water inflow will occur to the Foidel Creek Mine from the overburden units and possibly from the Trout Creek <br />Sandstone aquifer. Historically, no significant inflows from the Trout Creek sandstone have been detected. <br />Mine inflows may cause a temporary drawdown in the overlying undisturbed portion of the overburden units <br />and similarly in the Trout Creek Sandstone. Projections of mine inflows and unit drawdowns are discussed <br />under Rule 2,05.6(3)(b)(iii), Probable Hydrologic Consequences. The highest rate of inflow under steady -state <br />conditions was projected and measured to be about 645 gpm. This water was initially pumped into <br />Sedimentation Pond D and has been and will be pumped into both Sedimentation Pond D and to the Fish Creek <br />Water Treatment Facility. TC may pipe the water from Foidel Creek Mine Portal directly to Site 114 for use in <br />the underground operations. From Site 114, the water is pumped to the Million - Gallon Tank and eventually this <br />water is piped underground for use in dust suppression. <br />Portions or the overburden units are projected to be effectively dewatered immediately above active mining <br />areas and mined -out areas. TC's monitoring of the Wadge overburden unit verified this prediction. Drawdown <br />effects within the overburden units are expected to be contained within the Twentymile Park Basin limits during <br />active mining, but water levels are also expected to recover after mining ceases and the workings are allowed to <br />flood. As all wells completed in the units within the de- watering zone are owned by TC, no adverse effects on <br />other water users will occur. For mining to date, there is no substantive evidence indicating that any faults that <br />have been mined through were in hydrologic connection with the Trout Creek Sandstone. <br />Other than impacts from the pumping of Well FCM No. 1 (001 -83 -106), the only drawdown effects in the Trout <br />Creek Sandstone from direct mining activities will occur if significant communication with the mine workings is <br />established. The potential for this to occur is limited to major fault zones, and based on experience to date, the <br />potential is small. Projected drawdowns under worst -case conditions would probably be limited to the west - <br />central part of the Twentymile Park Basin. There will be some drawdown resulting from ongoing use of Water <br />Supply Well FCM No. 1, which is completed in the Trout Creek Sandstone_ The effects of this drawdown are <br />not projected to be significant. <br />Water levels may also be affected in the Twentymile Sandstone. Those areas, which are in subsidence zones, <br />are expected to experience water level declines. Based on monitoring of this sandstone near subsided areas of <br />the mine, the areal extent of the water level decline has been small. This is further discussed in Ground Water <br />Inflow to the Mine, below. <br />The potential effects of underground mining for the Foidel Creek operation have been generally discussed <br />earlier in the section. The following potential effects will be discussed more quantitatively in this section: <br />1) Ground water inflow to the mine <br />2) Dewatering and reduction of potentiometric levels in bedrock units <br />3) Diminution of bedrock discharge to alluvium and surface streams as a result of potentiometric <br />level reductions <br />4) Effects on ground water quality of unit systems following active mining and flooding of mine <br />workings and related subsided zones <br />5) Effects of discharge to alluvium and surface streams of ground water from flooded workings and <br />related subsided zones following active mining <br />Ground Water Inflow to the Mine <br />The underground mining activities at the Foidel Creek Mine have the potential to drain ground water from the <br />mined coal seam, and overlying and immediately underlying rock units. Bedrock units overlying and <br />underlying the Wadge and Wolf Creek coal seams, which contain ground water, would typically have formation <br />pressures higher that the atmospheric pressure that would exist in any open mine workings. Consequently, if <br />there is sufficient hydrologic communication, there will be movement of ground water from these units into the <br />active mine - workings. <br />TR13 -83 2.05 -134 11/03/14 <br />