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overburden unit to be affected within the proposed permit and adjacent areas are owned by TCC. The extent of <br />• effects is discussed quantitatively under Rule 2.05.6(3)(b)(iii), Probable Hydrologic Consequences. <br />Water inflow will occur in the Foidel Creek Mine from the overburden unit and possibly from the Trout Creek <br />Sandstone aquifer. As of June 1999, no significant inflows from the Trout Creek sandstone have been detected. <br />These inflows will cause a temporary drawdown in the adjacent undisturbed portion of the overburden unit and <br />similarly in the Trout Creek Sandstone. Projections of mine inflows and unit drawdowns are given under Rule" <br />2.05.6(3)(b)(iii), Probable Hydrologic Consequences. The highest rate of inflow under steady -stale conditions is <br />expected to be about 645 gpm. This water was initially umped into Sedimentation Pon D and has been and will <br />be pumped into both Sedimentation Pond D and - the FCB treatment facility TCC may pipe th water from Foidel <br />Creek Mine portal directly over to 14 for use in the underground operation. Ai Site 114 the water is pumped <br />to the million gallon tank and eventually – this water is piped underground for use in dust suppression. ✓ <br />The overburden unit is projected to be effectively dewatered immediately above actively mined areas. TCC's <br />monitoring of this unit verified this prediction. Drawdown effects within the overburden unit are expected to <br />extend to the Twentymile Park Basin limits during active mining but will recover after mining ceases and the <br />workings are allowed to flood. As all wells completed in the unit within the de- watering zone are owned by TCC, <br />no adverse effects will occur. To date, June 1999, 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.l (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. There is only small likelihood of this occurring along major fault zones. Projected drawdowns under <br />worst case conditions will probably be limited to the west- central part of the Twentymile Park Basin. There will be <br />drawdown resulting from the use of water supply well FCM No. I, which is completed in the Trout Creek <br />• Sandstone. The effects of this drawdown are not projected to be significant. <br />Water levels will also be affected in the Twentymile Sandstone. Those areas, which are in subsidence zones, are <br />expected to experience water level declines. Based upon monitoring of this sandstone near subsided areas of the <br />mine, the areal extent of the water level decline has been small. This is further discussed in Ground Water Inflow <br />to the Mine below. <br />The potential effects of the underground mining at 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; and <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 />�J <br />APPROVED JUN 2 8 2000 <br />PR 99 -05 2.05 -134 3/28/00 <br />