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SubTerra, Inc. Sage Creek Mine 11/18/2009 <br />Initial Evaluation of Subsidence Impacts for Continuous Miner Development <br />i s In our opinion, there is no potential for pillar punching, under worst case loading onditions, during <br />9 <br />continuous miner development of the Sage Creek Mine entries. <br />Potential Impact on Subsidence of Encountering an Unexpected Fault <br />While faulting may locally impact mine roof stability and pillar stability there is no prior evidence or <br />experience that faulting will have any impact on the magnitude of subsidence during mine <br />development. Provisions would be made for increasing roof support density and leaving larger <br />pillars if faults were encountered during mine development. In extreme conditions, where faulting <br />results in large in -seam displacements, entry development may be curtailed and plans revised to <br />relocate the longwall around the displaced seam. This extreme condition would not affect the <br />potential for subsidence to occur from continuous miner development. <br />In our opinion, encountering an unexpected fault will not affect the potential for mine subsidence <br />over the gate road entries. <br />Potential Effects of Encountering Gas or Water on Subsidence Potential <br />The Mine drainage system will be designed, as required, to transmit inflowing water from the point <br />of discovery to sumps where it can be removed and treated prior to disposal. Similarly, any gas <br />that is encountered will be diluted by the mine ventilation system and removed from the mine in the <br />return air stream. <br />In our opinion, encountering water or gas will not affect the potential for mine subsidence over the <br />• gate road entries when the described systems perform as described. <br />If the mine is allowed to flood, the effective stress will be reduced and the calculated pillar stability <br />factor will increase. There is no credible scenario that we are aware of that would reduce the <br />pillars stability factor under these conditions. <br />Potential Subsidence Damage / Need for a Subsidence Monitoring Prooram <br />In our opinion, there is no potential for subsidence damage to structures and renewable resource <br />lands under the current room and pillar mining proposal assuming worst possible conditions. <br />Furthermore, the potential for any measurable subsidence is so remote that the provisions of <br />Section 2.05.6(6)(b)(ii) (see Attachment A), requiring implementation of a Subsidence Monitoring <br />Plan should, in our opinion, be waived. This recommendation is supported by the requirements of <br />Section 2.05.6(6)(c) which were promulgated to address subsidence occurring during longwall or <br />retreat room and pillar extraction. A Monitoring Plan would therefore logically be required prior to <br />the onset of longwall mining at the Sage Creek Mine. <br />We trust that this report is sufficient for your present purpose. If you have any questions please do <br />not hesitate to call us at 425 - 888 -5425. <br />Sincerely, <br />Chris D. Breeds, PE, PhD, President <br />4 <br />