2014-11-17_PERMIT FILE - C1982056 (2)

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Wolf Creek Reserve Groundwater Investigation Work Plan March 6, 2014 Three wells are used to monitor water levels in the Fish Creek Sandstone. Water levels at the Ashley Well just south of the Wolf Creek Reserve dropped about 80 feet after subsidence in 1998, but afterward began to recover. Seasonal changes have been evident, but water levels have been near the original levels since 2001. Wells 91 M001 and 91 M004 were undermined in 1995 and exhibited historic water level declines corresponding to mining activity. Since 2002, water levels in well 91 M001 have risen slightly and water levels in Well 91 M004 have remained relatively steady, showing seasonal fluctuations. Numerous wells monitor water levels and quality in the alluvial aquifers. In general, the alluvium is recharged by streamflow, and water levels vary seasonally and in response to streamflow volumes and duration, not in relation to mining activities. The exception is in areas where mining - related subsidence results in lower ground surface elevations and surface water ponding. Inflows to the mine operations in the Wadge Seam historically have been small, with significant inflows encountered only occasionally when regional geologic structures were intersected. Annual inflow surveys conducted by TC personnel indicated that most of the mine area above the Wolf Creek Reserve was dry. Where groundwater was encountered, nearly all inflows were recorded as "dripping," and only rarely were inflows greater than 1 gpm recorded. The Wadge Seam above the Wolf Creek Reserve is mined out and filled with gob. Over time, slow infiltration and recharge will result in some storage, but vertical movement will be limited by the low permeability overlying and underlying units. Water Quality Groundwater from Wadge overburden wells is predominantly sodium - bicarbonate type with total dissolved solids (TDS) content ranging from about 900 to about 1900 milligrams per liter (mg /L). Well 006- 82 -74C, located immediately downgradient from the CYCC mine spoils, differs in being calcium - sulfate water with a TDS of about 2800 mg /L. Recent analyses of water from the Twentymile Sandstone showed sodium - bicarbonate water with a TDS of 1850 mg /L from well FBR -2 on the eastern permit boundary and sodium - bicarbonate - sulfate water with a TDS of 1110 mg /L from well 97013TM north of the Wolf Creek Reserve. Water from the Trout Creek Sandstone is typically sodium - bicarbonate water, sometimes with significant sulfate or carbonate, and with TDS in the range of 800 to 1000 mg /L. In most cases, TDS concentrations over the past five years have fluctuated slightly but not shown any well - defined trends. An exception is Trout Creek well FBR -2 -E, where TDS concentrations have decreased steadily since 2002. WOLF CREEK RESERVE EXPLORATION DRILLING Exploration drilling from the mine workings in the Wadge Seam was conducted to quantify available coal resources in the Wolf Creek Reserve and to obtain rock samples for quality and geotechnical characterization. Additional resource drilling is currently underway along the southern, eastern and northern perimeter of the proposed mining in the Wolf Creek Resource, where up to twenty holes will be drilled from the surface down through the Wolf Creek Seam. The locations of existing and planned drill holes are shown on Figure 3. While the underground exploration drilling was not conducted expressly for hydrologic data collection, observations during drilling indicated little to no groundwater in the interburden between the Wadge and Wolf Creek seams, and in the Wolf Creek Seam. No drilling fluid losses were noted as the holes were being drilled, and no artesian flow was observed at any of the drill sites after completing the holes. These conditions are likely a product of the fine- grained lithology of the interburden and depth, which result in very low permeability, and the past dewatering activities related to mining of the Wadge Seam. Decreasing permeability with depth has been documented in the region (Williams and Clark 1994, Robson and Stewart 1990), so the expectation of very low permeability of the interburden is supported. TETRA TECH 4