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C -1996 -083 TR -72 23- Mar -2012 <br />Geotech Review - MLT Page 2 of 3 <br />In January 2005, responding to Stipulation No. 16, BRL submitted an application for TR -36 <br />which included a new study prepared by Lambert. This study, dated January 13, 2005, <br />incorporated material characteristics for CMW produced by BRL's new processing plant. <br />Lambert found that the pile configuration used for the original design would not achieve the <br />required minimum FOS of 1.5, and that the slopes would need to be flattened. An additional <br />Lambert study, dated March 17, 2005, was submitted by BRL to address the Division's adequacy <br />concerns. This study determined that in order to achieve a minimum FOS of 1.5, the lower slope <br />would be reduced from 21-1: IV to 2.5H:1V, and the upper portion of the pile would be placed <br />with a slope of 5H:1 V. <br />Development of a new coverfill borrow area, immediately west of the original Gob Pile 42, was <br />proposed with TR -43. Excavation of material from the hillside, leaving a cut slope of 3H: IV, <br />was approved in September 2006. <br />In 2007, with TR -44, BRL proposed the westward expansion of the CMWDA, into the TR -43 <br />excavation area. This expanded area is also termed CMWDA 94. The application included a <br />February 1, 2007 Geotechnical Report prepared by Buckhorn Geotech, Inc. Buckhorn's <br />design(s) for this disposal area resulted in a pile height of 118 feet, an excavated slope of 2H:1 V <br />(or 2.5H:IV), with an outer CMW slope of 31-1: IV (or 2.51-1: IV). Both designs achieved a <br />critical FOS of greater than 1.50. On Page 12 of the report, Buckhorn recommended a <br />maximum excavation slope of 2H. 1 V, as this would provide a FOS of 1.50. Approval of TR- <br />44 increased the combined storage capacity of Disposal Areas 1, 2 and 4 from 800,000 to <br />1,075,000 cubic yards. <br />The quest for additional storage capacity for the prep plant's production of CMW continued with <br />BRL's September 2008 application for TR -56. This revision included Buckhorn Geotech, Inc.'s <br />September 22, 2008 Revised Stability Evaluations report. Following an analysis of material <br />properties, together with data from inclinometers and piezometers, the slope configuration of <br />CMWDA No. 2 was steepened, above the first bench, to 3H: IV overall. In addition, the design <br />considered an ultimate height of the pile of 300 feet. Various permit maps were updated under <br />TR -61 to incorporate modifications approved with TR -56. <br />The most recent modification to BRL's disposal of CMW came with TR -64 in December 2009. <br />A new May 18, 2009 Buckhorn Geotech study, "Revised Stability Evaluation of Coal Mine <br />Refuse Disposal Area No. 4 ", was incorporated into the permit. Based on Buckhorn's analysis, <br />the Division approved BRL's requests to increase the height of CMWDA No. 4 from 118 feet to <br />150 feet. The analysis utilized a 1.31-1: IV cut slope into the native soils beneath, but did not <br />determine a factor of safety for this slope, as it would be buttressed by placement of the CMW. <br />Another aspect of TR -64 was the "absorption" of the upper portions of CMWDA No. 1 into <br />CMWDA No. 4. <br />TR -72 Adequacy Comments <br />With respect to geotechnical information, the TR -72 application includes revised Maps 15 -3, 18, <br />and Volume IX Figures 1 and 2. Pages 1, 3, 4 and 11 of Volume IX have also been revised to <br />