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TCC is planning to recirculate underground water so that discharge to Fish Creek is not increased over the historic level during the NMD permit year. Therefore, there should be no quality impact to the streams due to the continued mining in the Northem Mining Districts. The exception to this is the short-term impact associated with dewatering the reservoir in the western mining district. This is discussed in TR 99-32. The mining in the NMD will result in subsiding areas where springs exist. TCC's experience is that there will be a temporary disruption in flow and then recovery of the springs. The reader is referred to TCC's 1996 AHR for further discussion of the recovery of springs SW 1 and SW2. No long-term impacts are anticipated to the springs in this area. In reference to Foidel Creek, TCC is not anticipating any significant impacts to the creek due to the mining of Panel 12 Right. TCC anticipates that the creek will react the same way it did previously. This reflects the fact that there are no sandstone outcrops intersecting the channel. Therefore, the potential to dewater the stream is non-existent based on TCC's prior experience with Foidel Creek given this condition, i.e. no outcrops in channel. The stream gradient for Foidel Creek is presented on Table 8, Exhibit 7e-3. TCC does not anticipate any significant erosional processes to be triggered by its' undermining and subsiding Foidel Creek. Impacts of Mining on Ground Water in the Fish and Foidel Creek Drainages The bedrock in the study area is composed of Lewis Shale in the Fish Creek valley and the central part of the Foidel Creek valley and of the Williams Fork Formation on the east and southeast parts of the Foidel and Middle Creek valleys. The Williams Fork Formation dips southwest. The original piezometric surface in the Wadge Coal Seam Overburden is estimated to be approximately 6,900 feet. The surface of ground water in the Wadge Coal Seam Overburden is now between elevations of 6,650 and 6,700 feet within the Foidel Creek AVF designated area, but is still approximately 6,900 feet in the northern part of the Twentymile Park basin. Ground water flows toward the northeast. The average hydraulic conductivity of the Wadge Coal Seam Overburden, verified by several tests, is • 0.32 ft/day. The potential water-bearing strata of the study area, above the Wadge Coal Seam, are the sandstones in the overburden of the Wadge Coal Seam, denominated as the Wadge Coal Seam Overburden, the Twentymile Sandstone, and the unconsolidated sediments in [he Foidel and Fish Creeks' alluvium. Only the Twentymile Sandstone is considered a significant aquifer. However, the Twentymile Sandstone is separated from the mined coal seam by a 500 to 600 foot-thick layer of marine shale called "Tongue of Lewis Shale." In most situations, this shale strata acts as a significant aquiclude above the mined coal. The Fish and Foidel Creeks' alluvium is composed mostly of floe-grained sediments, silts, silty clays, and clays in the areas to be subsided. The thickness and composition of the alluvial sediments was verified by the drilling of numerous alluvial wells and excavation test pits within the study area. The alluvial sediments are saturated and the water table, as measured in the existing monitoring wells along the Foidel Creek drainage area upstream and downstream of the study area, fluctuated during the annual seasons from 3 to 9 feet from the surface. The geologic composition of the Foidel Creek study azea is shown on Figure 7, Cross-Section of Alluvial Valley Lower Foidel/Middle Creeks Hay Meadows. This cross-section is located downstream of the proposed mining. In the Northem Mining district, the proposed longwall operations will be approximately 700-1,600 feet below the ground surface; the total thickness of the coal removed will be 8.0 to 8.5 feet. According to experience from the Appalachian and other coal fields, the extent of a zone with increased permeability above the longwall panel will reach approximately 30 to 40 times the thickness of the extracted coal seam. This conclusion is supported by information from the Foidel Creek Mine, where eleven ground water monitoring points were installed in the area of the Alluvial Valley Floor to monitor effects of subsidence. The monitoring wells and piezometers installed in the alluvium indicated no significant changes in water level or water quality. However, one monitoring well installed in a shallow bedrock sandstone had [o be replaced after casing failure and a Fr]~IP1~~5t~~ JUG! 2 g 2000 PR 99-OS 2.05-171.8 8/27/99