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<br /> <br />Excavation in the pond area extended the interior slope downward. Our analysis <br />considered this condition when developing analysis sections as discussed below. <br />Based upon Table I, we developed two conceptual analysis sections (Figs. 1 <br />and 2). The analysis sections were selected to incorporate the worst case conditions <br />for two groups of embankments. Group I (3 embankments) includes taller sections. <br />This group is highlighted on Table I. A total height of 22 feet, with a water storage <br />height of 10 feet, was selected for this group to reflect worst case conditions <br />considering excavation below the pre-existing grade at East Taylor. Group tl <br />includes the smaller sections with heights of 9 to 11 feet. For both groups the worst <br />case geometric conditions were incorporated into the conceptual analysis section. <br />This included the highest embankment height and highest level of water storage. <br />Also modeled were the steepest combination of interior and exterior side slopes <br />along with the minimum crest width. Although no one embankment has these <br />characteristics, the conceptual sections represent a worst case combination for each <br />group. <br />Construction Documentation <br />We reviewed available construction documentation for each sedimentation <br />pond provided by Colowyo Coal Company. The level of documentation varied for <br />each pond. All ponds have some level of documentation which, as a minimum, <br />indicates certification by a registered engineer that the ponds embankments were <br />constructed in accordance with the design and construction documents and <br />specifications. As would be expected, the documentation generally was more <br />detailed for the larger, more recent sedimentation ponds. In some cases, <br />documentation included design documents, construction specifications, photos <br />during inspection and/or density testing during construction. <br /> <br />COLOWYO COAL COMPANY, LP <br />STABILITY EVALUATION • SEDIMENTATION PONDS <br />CTLlT Y8,233 ~ <br />