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<br />34 <br />the geologic conditions." <br />(7)"A three layer model was selected to represent the spoil, soil layer and underlying <br />bedrock. Our experience indicates the sedimentary bedrock possesses sufficient strength <br />so that failure through the bedrock is not a consideration." <br />(8)"The angle of repose is considered a good indicator of friction angle." (Exhibit #13, <br />page 9, first paragraph) <br />CTL/Thompson, Inc. is straight forward in relating the assumptions made in completing <br />it's preliminary analysis. In appraising the conclusions based upon such a preliminary <br />parametric analysis the reviewer must condition his conclusions upon those limiting <br />assumptions. If conditions in reality differ from those assumptions, the conclusions of the <br />conditioned analysis are rendered inappropriate and inapplicable. I consider all of <br />CTL/fhompson's limiting assumptions, except the last two, to be appropriate. <br />The Choice of a Three Layer Model for Fills Analysis - (7) above <br />Examination of the permit application documents have discerned an apparent <br />inconsistency in regazd to the specific relationship of the proposed fills, the lowermost <br />surface mined coal seam, and the backfilled spoil within the mined area. The text <br />descriptions included within the "2.05.3(2) Operations Description -First Permit Term" <br />section of the application suggest that the 21 proposed fills will be constructed below the <br />elevation of the lowermost surface mined coal seam, as is the case for the traditional head <br />of hollow fill. If this is indeed the case then the simplistic three layer model of spoiUclay <br />soillbedrock chosen by CTLII'hompson, [nc. might be appropriate. However, the cross <br />sections included within the "2.05.4 Reclamation Plan ... Backfilling and Grading" <br />section of the text (Figures 2.05.4-1 through 2.05.4-14) depict many of the fill tops higher <br />in elevation than the adjacent backfilled spoil. The top of Fill #4, for example, is <br />depicted on figures 2.05.4-8 and 2.05.4-9 as being approximately 170 feet above the <br />adjacent lowermost extracted seam. This is in significant disagreement with the <br />generalized (spoiUclay soil bedrock) fill sections analyzed within Exhibit #]3 and <br />represented as typical of the proposed spoil fill structures. Founding these fill structures <br />partially on spoil abutments might significantly affect the material parameters and cross <br />sectional configurations used within the stability analyses. <br />The applicant must resolve these apparent inconsistencies. The application should first <br />be revised to clarify the relationship of the proposed fills, the lowermost mined seam, and <br />the adjacent backfill. Following resolution of this existing confusion, CTL/Thompson, <br />Inc. May need to formulate a more complex and appropriate model for use in the revision <br />of its generalized preliminary analysis and future completion of the required site-specific <br />fill stability analyses. <br />Relationship of the Angle of Repose and the Internal Friction Angle - (8) above <br />