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i~ <br />• or cover areas should be prepared if auger areas remain uncovered for more than <br />2 years. <br />The web widths were conservatively designed with factors of safety of 1.5 to <br />2.0 or greater to allow for strength variation or reductions due to oxidation or drying. <br />We do not anticipate significant strength reductions due to these factors. <br />Subsidence <br />We do not believe that surficial effects due to auger mining are a significant <br />concern. The auger mining will not adversely affect the stability of the excess spoil <br />pile. Three subsidence mechanisms were evaluated to evaluate possible surface <br />effects; elastic deformation, chimney subsidence and pillar (or web) collapse. <br />Based upon an assumed elastic modulus of 250,000 psi for the coal pillars, <br />. elastic deformation due to auger mining is estimated to be on the order of 0.2 inches <br />where auger mining of the X-seam is performed (Streeter Pit Area). Where 3 seams <br />are angered (West Pit) the elastic surface deformation is expected to be on the order <br />of 0.5 to 1 inch. The elastic deformation in both areas is considered negligible. <br />Chimney subsidence is considered very unlikely where the depth of <br />overburden to mined height ratio is greater than a value ranging from 5 to 10. This <br />ratio depends on the shape and bulking factor assumed15. The ratio for X-seam <br />auger mining (assuming a 7 foot diameter mined height) is about 29 for the Streeter <br />Pit Area, in the West Pit the ratio is over 12. For deeper seams the ratios are higher. <br />The possibility of chimney subsidence affecting surface features in the West Pit or <br />Streeter Pit areas is considered extremely remote. <br />Failure of the pillars (webs) left after auger mining was evaluated. In the <br />Streeter Pit area the web widths were designed using a factor of safety of 2 applied <br />• to a conservative estimate of coal strength. We believe the possibility of large scale <br />pillar failure over an area sufficient to produce surface effects is very low. <br />COLDWYO COAL COMPANY, L. P. <br />CTL/7 2].SBS 1 O <br />