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Hwddlo a -Deny <br />s- ,- ",aer., u, <br />The evaluation was completed by a Colorado registered professional engineer in <br />accordance with generally accepted geotechnical engineering practices. This report has <br />been prepared for the exclusive use of Bowie Resources, LLC. <br />2.0 BACKGROUND <br />The available reference documentation indicates that the original geotechnical <br />investigation was completed by Lambert and Associates (Lambert) in 2003 and that <br />placement of coal mine waste at gob pile #2 began in 2004. Additional evaluation of the <br />stability of gob pile #2 was completed by Lambert and Buckhorn Geotech, Inc. <br />(Buckhorn) in 2005. Based upon the results of these analyses, maximum slopes of <br />5H:1 V were specified for gob pile #2. However, this was based upon the assumption that <br />undrained (total stress) conditions would exist within the gob pile. <br />As part of their work in 2005, Buckhorn installed vibrating wire piezometers and <br />inclinometers in gob pile #2. As a result, based upon the availability of pore pressure and <br />inclinometer data, Buckhorn re- evaluated the stability of gob pile #2 in 2008. At that <br />time, the available data suggested that undrained conditions did not exist within the gob <br />pile. Therefore, Buckhorn completed drained analyses and determined that the upper gob <br />slopes could be increased from 5H:1 V to 3H: I V. Since 2008, coal mine waste has been <br />placed on gob pile #2 to achieve slopes of 3H:1 V. <br />Continuing operations at the site are anticipated to include placing uncompacted, <br />wet gob on top of gob pile #2 to allow it to dry. Final placement and compaction will <br />occur after the material has been allowed to sufficiently dry. Based upon information <br />provided to HBET, the uncompacted, wet gob will be placed on top of gob pile #2 <br />approximately 20 feet high. The uncompacted gob will be set back from the crest of the <br />finished gob pile slopes approximately 25 feet. The gob will be end dumped such that <br />the uncompacted gob is anticipated to have a face slope angle of approximately 1.5H:1 V. <br />3.0 STABILITY ANALYSES <br />3.1 General <br />In order to evaluate the stability of the existing gob pile #2, HBET utilized cross <br />sections generated by J.E. Stover and Associates based upon available survey data. <br />Analysis of the gob pile was completed utilizing the GeoSlope GeoStudio 2007 <br />SLOPE /W software package. <br />During our review of the available documentation, HBET observed that some of <br />the analyses were completed using Spencer's method. However, some of the analyses <br />were completed using the simplified Janbu method. The simplified Janbu method does <br />not consider both force and moment equilibrium whereas the Spencer method does. In <br />general, HBET believes that the Spencer method is mathematically more robust and <br />provides a more accurate assessment of stability of slopes. As a result, HBET used the <br />Spencer method in our analyses. <br />X.12008 ALL PROJECTS'00489 - IF Stover Associates 1nc'00489 -0003 BoNie %ftne1200 - Geo'00189 -0003 R032114RI doc 2 <br />