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Monitoring results from the Fish Creek alluvial wells and associated surface sites (AVF -14, SW -14, 008 -AU3, <br /> and 305) were consistent with surface observations and surveys, indicating no significant subsidence - related <br /> changes in flows or water quality. <br /> • Subsidence Cracks The potential occurrence of subsidence cracks is another feature that could disrupt the <br /> surface and shallow ground water regime. The current experience from Pennsylvania and West Virginia, <br /> supported by other experience gained from mines in the Somerset, Paonia areas in Colorado, indicates that <br /> subsidence cracks may develop in areas of low overburden and on bedrock outcrops. The subsidence <br /> monitoring conducted at the Fish Creek AVF study area, immediately downstream of the RCR27 culvert in Fish <br /> Creek in the WMD, did not indicate any visible cracks in the Fish Creek channel. Subsidence cracks occurring <br /> across a stream channel could cause the disruption of the stream. However, because of the presence of thick, <br /> fine- grained sediments in the stream bed of the study area, the cracks will naturally seal quickly, and no <br /> significant impacts on flows are expected. <br /> The occurrence of the subsidence cracks on the surface may not necessarily result in direct inflow into the mine <br /> when a surface water body was disrupted. Studies by various authors such as Orchard (1969, 1975) in Great <br /> Britain, Williamson (1978) in Australia, and Hydro -Geo Consultants, Inc. in West Virginia (1991) and Ohio <br /> (1988), indicated that the subsidence cracks are limited in depth by the development of compressive stresses <br /> replacing the tensile stresses that cause surface fracturing. The depth of surface subsidence cracks due to tensile <br /> stress does not typically exceed 50 feet. Development of this type of crack would be limited in the <br /> unconsolidated sediments of the Foidel and Middle Creek alluviums, which are to 30 feet thick near the <br /> confluence of these two streams. The presence of up to 600 feet of marine shales between the ground surface <br /> and the mined coal will also limit the impacts of subsidence. <br /> TCC has done considerable subsidence monitoring work at the Fish Creek AVF study area, area immediately <br /> downstream of RCR27 culvert in Fish Creek in the WMD, to determine if subsidence would impact the creek <br /> and its Alluvial Valley Floor. One component of the work focused on making visual observations of Fish Creek <br /> 0 to determine if any cracking was occurring in the creek channel. The channel included sections of both <br /> sediment and exposed bedrock. The visual observations, which included those made by representatives of the <br /> DMG, indicated that no cracking of the channel occurred during longwall mining. <br /> Subsidence Effects on Springs and Seeps Mining in the NMD and WMD will result in subsiding areas where <br /> springs and seeps exist. TCC's experience is that there will be a temporary disruption in flow, and then recovery <br /> of the springs. Refer to TCC's 1996 AHR for further discussion of the recovery of Springs SW1 and SW2. No <br /> long -term impacts are anticipated to the springs and seeps in these areas. <br /> GENERAL SUMMARY AND CONCLUSION <br /> The described streamflow and water quality impacts for expansion of underground mining into the EMD at the <br /> Foidel Creek Mine are within the limits of impacts discussed by Kaman Tempo (1982) and by Parker and Norris <br /> (I 983) relative to the study area. It is apparent that such hydrologic impacts are relatively greater in stream <br /> reaches near mine discharges. Mine discharges may be treated, as necessary, to reduce levels of total suspended <br /> solids, and possibly to settle out oxidized trace metals prior to discharge to a stream. For the most part, <br /> dissolved solids and major ionic solute concentrations associated with mine flows will be unaffected by <br /> treatment, and will be mixed with receiving stream waters. Total Recoverable Iron will be removed by the FCB <br /> treatment facility at Site 115. <br /> Dissolution of soluble minerals will occur as a result of the process of dewatering and handling of discharged <br /> water from the underground mine. Because ongoing underground mining opearations, and adjacent surface <br /> mined areas are located in areas recharging groundwater to the overburden unit,. hydro - geochemical changes in <br /> water flowing through this unit have already occurred and are expected to continue. The supporting analysis <br /> e conducted to assess these changes is included in the groundwater PHC section. <br /> PR09 -08 2.05 -164 04/29/09 <br />