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of discharge from the Area 2 Pit. SAR values could increase slightly as a consequence, but the magnitude of <br />increase should be slight and would depend upon the degree of cation exchange within the waste rock placed in <br />09 the Area 2 Pit. <br />The inflow to the 6 -Right Gateroad area began in the November and December of 1997. A comparison of the <br />inflow rates to streamflow data (Exhibit 5 1, Figure E51- 1) does not indicate any impact to the stream flow <br />from the increased mine inflows. The stream flows before and after the inflows began are very similar and both <br />the mine inflows and the stream inflows appear to be responding to seasonal variations in recharge and runoff. <br />A comparison of the surface water quality of the 6 -Right inflow to that of Foidel Creek water (Site 8) and to <br />spoil water (Well 26 -SP -2) is inconclusive (Exhibit 51, Table E51 -1). The 6 -Right water and the spoil water <br />have similar conductivity, dissolved solids and bicarbonate concentrations. While the 6 -Right water is similar to <br />the spoil water, it has an elevated sodium concentration. This may be due to ion exchange (see Exhibit 38 and <br />discussion above on mine inflow water quality. However, the calcium and magnesium concentrations of the 6- <br />Right water resemble that of Foidel 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 <br />development 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 <br />the 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 visible in <br />unconsolidated sediments. <br />Differential vertical settlement over a short distance will result in local changes in ground surface slopes. If 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 pending. <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. Middle Creek is also an intermittent stream with headwaters <br />approximately 10 miles upstream from the confluence with Foidel Creek. Middle Creek joins Trout Creek <br />approximately 1.5 miles northeast of the Middle Creek/Foidel Creek confluence. Fish Creek is a perennial <br />stream with headwaters in the Dunkley Flattops area. Fish Creek flows through much of the mining area and <br />joins Trout Creek approximately 1 mile north of the Trout Creek/Middle Creek confluence. <br />Predicted Impacts - 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 />PR09 -08 2.05 -160 04/29/09 <br />