2015-02-26_REVISION - C1982056 - Laserfiche WebLink

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Development and future mining of the Wolf Creek Reserve will result in limited mine water inflows to the Wolf Creek mine workings, but more significantly, will require dewatering of two existing mine water pools in the overlying sealed mine workings in the Wadge Seam in the center of the NMD, and the southern portion of the EMD. The overlying mine water pools will be drained prior to mining in the Wolf Creek Seam, as a safety and operational consideration, by drilling and completing one or more inter -seam dewatering well(s) from the Wolf Creek Seam up into the mine pool areas in the Wadge Seam workings. The resulting mine pool drainage will be transferred from the inter -seam dewatering well(s) to the NW Mains underground sump, from which the water can be transferred anywhere within the existing mine water handling system. In addition to the inter -seam dewater well(s), TC plans to complete one or more underground horizontal drillholes into the AND to allow water to be transferred into the sealed workings of the WMD, once mining is completed in this area. Mine pool drainage may be stored in the underground workings, transferred through the mine water handling system for use in either the Washplant or for underground operations (mine dust control), discharged under TC's existing CDPS Permits, or (most likely) a combination of these. It should be noted that the initial development activities for the Wolf Creek Seam have been planned and laid -out so that dewatering will not be required for this initial phase. Inflows to the WCR under full development, based on the observed 0.027 gpm /acre rate previously mentioned for the SWMD, and a total WCR mine area of approximately 4,690 acres, are estimated at 125 gpm. The two underground mine water storage reservoirs, in the SWMD (dewatered by Fish Creek dewatering boreholes), in the EMD (dewatered by the IORT 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 intermittently to maintain water levels below these maximum water level elevations. Timing and water duality 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 and Wolf Creek overburden units will cause dewatering and potentiometric drawdown in the units. Where the Twentymile Sandstone directly overlies the mine workings, it may also be affected. To date, no measurable impacts to the Trout Creek Sandstone related to mine dewatering have 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. Well FBR -2, completed in the Twentymile Sandstone, showed a water level decline of about 190 feet during mining of the eastern end of the nearby 16RT panel but has since recovered about 120 feet. Well 97013TM, completed in the Twentymile Sandstone slightly north of the 20RT panel, experienced an overall water level decline of about 120 feet from 1998 to 2012 and has since remained stable. 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 affected by ongoing and 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 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 impacts on water levels in the Twentymile Sandstone. The proximity of the Wadge and Wolf Creek overburden/interburden units to the mined zone and the expectation of subsidence- induced fracturing will result in dewatering of the units immediately above and adjacent to active mine areas. Drawdown of potentiometric levels in these units will occur beyond the area of active mining as a result of lateral movement of ground water toward these areas. Groundwater monitoring data presented in the Annual Hydrology Reports submitted through 2013 indicate that water levels in Wadge PR14 -10 2.05 -139 12118/14