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r, drop in water level. This was attributed to the casing being pinched off at the interface between sandstone and shale after undermining. This well failure is attributed to near-surface cracks in Subsidence Zones 4 and 5. The geologic conditions of the Northern Mining District is very favorable for limiting the impacts of land subsidence on hydrology. The presence of 600 feet of marine shale above the mined coal and the limited extent and fine character of the unconsolidated sediments in the local valleys would reduce any potential subsidence impacts. The presented interpretation of the impacts of subsidence on the water-bearing strata in the study area is supported by numerous studies in various coal fields worldwide. Impacts ou Ground Water Quality The potential impacts of subsidence on ground water quality could develop in the following ways: Caved overburden materials replace part of the coal seam aquifer; and Fracturing develops a new hydraulic connection between aquifers with different water quality. The first example is applicable only in cases where the coal seam acts as an aquifer, which is not the case in the study area. The second example is more common in cases where several aquifers with different water quality are present. In the Foidel and Fish Creek alluvium areas, the potential interconnection could be, for example, between the Twentymile Sandstone and the alluvial aquifer. One apparent impact to the Twentymile Sandstone from subsidence is the drop in water level in monitoring well 006-82-48A. This drop in water level is attributed to a possible mechanical failure of the casing and loss of the well seal or increased porosity resulting ina lowering of the water level. Monitoring well 006-82-48A was installed in a borehole that had originally been drilled through • the Twentymile Sandstone to the Wadge Seam. Although subsidence may have precipitated the destruction of this well, no impacts on the ground water quality in the Foidel and Middle Creek alluviums are anticipated. This conclusion concurs with [he experience in other coal fields. Most of the studies of subsidence effects of surface and ground water quality in the Appalachian coal fields concluded that no significant long-term effects on water quality were observed, which confirms observations from the Foidel Creek Mine (Owili-Eger, 1987; Moebs and Barton, 1985; Schultz, 1988). Couclusious The conclusion regarding the potential impacts of the CTCC longwall operation in the Northern Mining District on the local surface and ground water resources is that the effects will be very limited due to the depth and lithological composition of the overburden above the mined Wadge Coal Seam. Impacts on surface and ground water resources are possible within 340 to 380 feet above the mined coal seam and within an angle of draw of about 17 degrees from the longwall panels. An analysis of the geologic composition of the Wadge Coal Seam Overburden indicated that only limited sandstone strata in the mined coal seam overburden are impacted by subsidence. The conclusion is confirmed by the limited ground water inflow into the current mining operation. The predicted ground surface subsidence within the Foidel Creek alluvium would reach up to 46 inches during mining in panel 12 Right, where the overburden is 600 feet thick (SubTerra, Inc., 1996). This rate of subsidence could cause short-term changes in the Foidel Creek stream gradient. However, the calculated maximum slope change (SubTerra, Inc., 1999) of 0.6% (Panel 12 Right) would not have any significant long-term impact on the stream flow and/or water quality. The meandering character of Foidel Creek, cutting through fine-grained sediments, would facilitate the fast-healing process of any temporary changes in the streambed gradient. The predicted ground surface subsidence for the Fish Creek alluvium would reach up to 60 inches during mining in ~` panel 13 Right, where the overburden is 1,400 feet thick (SubTerra, Inc., 1999). This rate of subsidence could cause short-term change of the Fish Creek streambed gradient. The maximum stream bottom gradient projected for PR 99-OS 2.05-171.9 8/27/99