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discussion above on mine inflow water quality. However, the calcium and magnesium concentrations of the 6 <br />• Right water resemble that of Foide! Creek. <br />Subsidence Impacts on Surface Water <br />Subsidence due to longwall mining can impact surface streams or impoundments in the following ways: <br />• Vertical settlement of the surface; <br />• Local changes in surface slopes: <br />• Vertical or sub-vertical subsidence cracks caused by tensile strain. <br />The degree of impact depends on local topographic and geological characteristics in addition to the mining <br />parameters. The degree of vertical subsidence and changes in surface slope can be calculated and the development <br />of surface fractures can be predicted from the mining parameters. <br />Vertical settlement can have an impact on any hydraulic system, natural or man-made, which depends on gravity <br />flow. Natural streams, ponds, and ditches can be disturbed by sudden changes in surface configuration. <br />Subsidence can either cause an increase or decrease in local ground surface slope. The change in the gradient of <br />any stream channel can have an impact on the stream by changing its Flow characteristics and material transport. <br />Vertical settlement of identical magnitude over large areas has frequently a negligible effect on surface water <br />bodies. The changes of stream gradient are minor (if any) and the vertical displacement has very little effect on the <br />impoundments, such as stock ponds. The magnitude of the vertical settlement is dependent on the materials <br />underlying the stream bed. The impacts would be more pronounced in the bedrock and much less <br />visible in unconsolidated sediments. <br />• Differential vertical settlement over a short distance will result in local changes in ground surface slopes. !f such <br />changes occur along any stream channel, its gradient will change. Any gradient changes will impact the stream <br />characteristics (flow and material transport). In an extreme case, the gradient changes could disrupt the flow and <br />cause ponding. <br />Subsidence Impacts on Foidel, Middle and Fish Creeks <br />Foidel Creek is an intermittent stream with headwaters approximately 5 miles upstream of the permit boundary. <br />Foidel Creek is a tributary to Middle Creek, and the confluence of these streams is approximately 3,000 feet <br />downstream of the proposed mined area. <br />Predicted Im~cts -Foidel Creek The Foidel Creek stream flow monitoring has been performed within the <br />permit area at three stations. USGS Stations 09243800 and Site 8, located within the undermined area and <br />upstream of panels 4 and 5, and USGS Station 09243900, located on the eastern end of the undermined area. <br />USGS Station 09243900 had a range of mean annual Flow from 0.07 cfs in 1977 to 4.39 cfs in 1981, during a <br />period of record from October 1975 through 1992. High flow occurs during the snowmel[, typically in April <br />through June, and low Flow occurs typically in July through September. The potential changes in the Foidel Creek <br />gradient due to surface subsidence caused by the longwall mining in panels 9 Right through 6 Right were <br />estimated. This estimate is based on the characteristics of Foidel Creek and results of the ground surface <br />subsidence study presented in Exhibit 7E of this application. <br />• <br />AE°~R~~rHD JUN 2 8 2000 <br />PR 99-OS 2.05-161 03/28/00 <br />