2010-06-04_PERMIT FILE - C1982056A (10)

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GROUND WATER SYSTEM •A detailed discussion of ground water hydrology is presented under Rule 2.04.7(1). The proposed life -of -mine area for the Foidel Creek Mine is located within the Twentymile Park ground water basin. The Twentymile Park Basin is an enclosed ground water basin. Therefore, any mining related impacts on the ground water hydrologic system should be confined within the basin. Potential Mining Related Impacts on Ground Water Quantity and Quality The mining and related operations have the potential to locally affect the water levels, and the water chemistry of the ground water contained in the Wadge overburden unit, the Twentymile Sandstone aquifer and the Trout Creek Sandstone aquifer. The Wadge overburden unit will be directly affected due to removal of the Wadge Coal Seam, which is at the bottom of the unit. The Twentymile Sandstone and the Trout Creek Sandstone aquifers may be affected if significant hydrologic communication is established with the underground workings. This is not likely to occur except in the vicinity of major fault zones or if greater than predicted subsidence results, due to the existence of thick, intervening bedrock sequences of very low permeability as described in the general description of geology and hydrology (sections 2.04.5, 2.04.6 and 2.04.7). To date, June 1999, no significant hydrologic communications have been encountered with these two aquifers. During the mining operation, the major ground water effects will be on water quantities in the immediate overburden. Ground water inflows from the overburden sequence into the mine workings will cause dewatering of the sequence near the mine and will cause drawdown of potentiometric levels at some distance from the mine. If significant hydrologic communication is established with the Twentymile Sandstone or the Trout Creek Sandstone then drawdown of potentiometric levels in these units will also occur. Discharge of these bedrock aquifers to surface streams may be reduced as a result of these drawdowns. The extent of these effects is examined in more • detail under Rule 2.05.6(3)(b)(iii), Probable Hydrologic Consequences, of this revision application. No water quality effects in these units are anticipated during the mining operation, as flows will be from the units to the workings. Mine inflows will be collected in sump areas within the mine and pumped to the surface where they will be treated and discharged to surface streams. The effects of this operation on surface water flows and quality are discussed under Rule 2.05.6(3)(b)(iii), Surface Water Probable Hydrologic Consequences. After mining operations at the Foidel Creek Mine have been completed and the mine workings are allowed to flood, there is the potential for water quality effects on units that are in communication with the workings. The increased surface area of rock material that has been exposed to weathering is more susceptible to leaching by the ground water in the flooded workings. This may lead to increased solute concentrations and changes in water chemistry characteristics. As pre- mining potentiometric levels and ground water, flows are re- established, discharge of this lower quality water to other units and to surface streams is occurring. The effects of this occurrence are discussed under Rule 2.05.6(3)(b)(iii), Probable Hydrologic Consequences Ground Water System Effects on Ground Water Quality of Aquifers. Leaching of waste rock material in disposal areas upgradient from the underground mining operation, and of caved and fractured material in and above the mined workings is unavoidable and will result in increased TDS levels in affected Wadge Overburden ground water unit. Once leaching has occurred, there is no practical technology currently available to treat the water to decrease TDS concentrations. Decreases in TDS levels will occur after sufficient water has percolated through the newly exposed material; however, this may take several hundred years under existing hydrologic conditions. The only method to minimize the impacts of mine - related leaching on ground water quality is to minimize the amount of water, which can pass through these materials. The effects of this leaching are discussed in Effects on Ground Water Quality of Aquifers and Surface Water Systems Impacts of Mine Discharge below. It should be noted that despite some unavoidable increase in TDS concentrations or change in ion balance, the overall ground water impacts are limited to this relatively unimportant overburden unit. Water supply wells in the PR 99 -05 2.05 -133 APPROVED JUN 2 8 2000 328/00