2009-10-30_PERMIT FILE - C1982056A (5)

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SWMD, where it will report to the Fish Creek Borehole sump, and can be transferred to the Barricade Chamber, the Area 1 Pit, or discharged to Fish Creek at Site 115. • The two underground mine water storage reservoirs, in the SWMD (dewatered by Fish Creek dewatering boreholes), in the EMD ( dewatered by the TORT dewatering boreholes), provide an estimated storage capacity of approximately 1,410 and 2,540 acre -feet, respectively. In order to maintain adequate freeboard (approximately 25 feet below the minimum seal elevation = 5,935 ft for SWMD, and 5,889 ft for EMD), the storage pools are now being pumped intermittantly to maintain water levels below these maximum water level elevations. Timing and water quality issues related to mine water discharge are discussed in "Effects on Ground Water Quality of Aquifers and Surface Water Systems Impacts of Mine Water Discharge ". Dewatering and Potentiometric Drawdown in Bedrock Units Projected inflows to the mine from the Wadge overburden unit will cause dewatering and potentiometric drawdown in the unit. Where the Twentymile Sandstone directly overlies the mine workings, it will also be affected. To date, no measurable impact to the Trout Creek Sandstone has been observed, and water quality data from mine inflows does not indicate any significant connection to either the overlying Twentymile Sandstone or the underlying Trout Creek Sandstone. Well 006- 82 -48A, completed in the Twentymile Sandstone, showed a rapid water level decline before being rendered inoperable due to being undermined by a longwall panel. Other Twentymile Sandstone wells, however, which are not directly underlain by mine workings, do not show any direct impact from mining. Major fault zones are not expected to provide significant conduits for ground water flow through the marine shale in the part of the basin underlain by the proposed mining activities. This is due to the nature of the marine shales and the high overburden stress in this area, which would tend to keep the fault zones closed. Appreciable ground water flows through fault zones has only been observed at the basin margins where overburden stress is S relieved. Well BRDH -7 is located approximately one -half mile from the mine workings and has not shown any significant water level decline (Figure 12a). Future mining is expected to have only localized impact on water levels in the Twentymile Sandstone. The proximity of the Wadge overburden unit to the mined zone and the expectation of subsidence - induced fracturing will result in dewatering of the unit immediately above and adjacent to active mine areas. Drawdown of potentiometric levels in this unit will occur beyond the area of active mining as a result of lateral movement of ground water toward these areas. The extent of potentiometric lowering was investigated using the finite- difference simulation model described in Exhibit 13, Ground Water Model Documentation. The model did not account for mine inflow derived from dewatering of the overburden directly above active mining areas. However, this does not invalidate the prediction of drawdown effects as this is based on the estimates of lateral movement toward mined areas which was correctly assessed. The extent of potentiometric lowering is illustrated by predicted drawdown after 5 years of mining (starting in 1983) and it is shown on Figure 13, Predictive Analysis After 5 Years of Mining. This figure indicates that drawdown effects will extend to the outcrop areas of the overburden unit at the margin of the Twentymile Park Basin. Evaluation of data from observation wells indicates that these predicted effects are probably overestimated. Recovery of potentiometric levels within the overburden unit will occur following mining through recharge of the unit, primarily at the basin margins. Subsidence effects will cause fracturing and rubblization of the overburden unit, so that its postmining permeability will initially be much higher than typical premining values. Consequently, the rate of potentiometric recovery will primarily be governed by the rate of recharge. • Recharge to the mine workings will primarily be from the updip spoils area of the adjacent Eckman Park surface mine. During mining, and for most of the recovery period following mining, the workings and overlying overburden adjacent to these spoils areas will not be saturated i.e. the effective potentiometric head will be at the elevation of the base of the mined zone. The spoil at the old highwalls is expected to be fully saturated under reclaimed conditions, as is the case near the Foidel Creek Mine portal area. The effective potentiometric head in PR09 -08 2.05 -139 08/25/09