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➢ A slope of 2.5H:1 V (horizontal:vertical) for the first 50 vertical feet of the stockpile <br />(beginning at the toe). <br />➢ A slope of 5H:1 V above the first 50 vertical feet to an ultimate height of approximately <br />210 feet. <br />➢ Fifteen -foot wide terraces at 50 vertical foot spacing, graded for drainage to the lateral <br />diversion ditches. <br />According to Dunrud (1989), geology of the Bowie mine area in general, and the coal waste <br />stockpile in particular consists of nearly flat Cretaceous sedimentary bedrock units. Mancos <br />Shale is mapped near the bottom of the valley slope with the Rollins Sandstone overlying the <br />Mancos Shale. On the north side of the valley, the Mancos Shale is covered with colluvial <br />deposits. The Rollins Sandstone outcrops can be observed above the current coal waste <br />stockpile. <br />3.0 SITE INVESTIGATION <br />A drilling investigation has been conducted by Buckhorn at the coal waste disposal area for the <br />Bowie No. 2 mine. A total of eleven boreholes have been drilled to date to sample and <br />characterize the coal waste and native materials and install instrumentation to monitor pore <br />pressure and ground movement within the coal waste. The drilling program and installed <br />instrumentation are discussed in this section. <br />3.1 Drilling Program <br />A total of eleven boreholes were drilled at the coal waste stockpile in June, August, and <br />December 2005. The boreholes, designated BG05 -01 through BG05 -11, were drilled with a <br />Simco 2800 H.S. truck - mounted drill rig. Locations were selected to attempt to characterize the <br />overall gob material. However, subsurface information and samples are necessarily limited to <br />eleven boreholes. <br />Boreholes BG05 -01 through BG05 -03 were drilled in June 2005 on top of the coal waste <br />stockpile platform at approximate elevations of 6,060 feet. As indicated on the attached Site <br />Plan, BG05 -01 was drilled on the eastern side of the platform, BG05 -02 was drilled on the <br />approximate maximum section (central portion) of the platform, and BG05 -03 was drilled on the <br />western side of the coal waste stockpile platform. Boreholes BG05 -04 through BG05 -07 were <br />drilled along the 20 -foot wide bench constructed approximately 50 vertical feet above the toe of <br />the coal waste stockpile. BG05 -04 was drilled on the eastern side of the bench, BG05 -05 and <br />BG05 -06 were drilled adjacent to each other near the maximum section of the coal waste <br />stockpile, and BG05 -07 was drilled at the western side of the bench. Boreholes BG05 -01 <br />through BH05 -07 were logged and sampled in the field by a geotechnical engineer. Boreholes <br />BG05 -08 through BH05 -11 were drilled in December 2005 on top of the coal waste stockpile <br />platform. The boreholes were drilled solely to obtain thin - walled "Shelby tube" samples for <br />triaxial shear testing. Therefore, these boreholes were not logged. <br />Bowie No 2 Gob Pile Stability Dec2005 <br />Project 405- 126 -GEO <br />Page 5 of 18 <br />