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SubTerra, Inc. Twentymile Coal Company 04/07/09 <br />Foidel Creek Mine <br />Permit Revision PR09 -08 Subsidence Evaluation <br />6. Conclusions and Recommendations <br />The evaluation summarized in Section 3 indicates that minor impacts are predicted as a result of <br />subsiding County Road 27 in the Western Mining District at the Foidel Creek mine. Mitigation is likely <br />to be confined to cold patching of cracks that may appear in the road surface during undermining. <br />The evaluation presented in Section 4 predicts that Fish creek will overflow its high bank(s), primarily <br />above 15 -Left in the Western Mining District at the Foidel Creek mine. Subsidence is predicted to <br />have the following impacts on Fish Creek and its AVF: <br />1. A maximum increase in creek bottom gradient of 0.007 (0.7 %). <br />2. Increase in the surface area of Fish Creek from 9.2 acres to 50 acres following excavation <br />of Panels 15 through 13 -Left. <br />3. Temporary increase in Fish Creek's surface area to 77 acres during peak flow conditions. <br />It is our understanding that the magnitude of predicted surface water area changes in the Northern <br />Mining District contained in our 1999 and 2002 reports were never realized illustrating the <br />conservative nature of these predictions. This is likely due to the dynamic process where <br />differential subsidence displacements are readily accommodated by the natural processes of <br />erosion and deposition that occurs rapidly under the high flow conditions experienced during spring <br />months. <br />If you have any questions regarding the above, please do not hesitate to call us at 425 - 888 -5425. <br />C0 Best Regards <br />Chris Breeds, PE, PhD <br />President <br />C0 <br />PN: 2009 -04 <br />