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0 <br />Photo taken looking east along the foundation excavation bench (near <br />the proposed toe of refuse) for the CWDA No. 4 footprint during the <br />geotechnical investigation. CWDA No. 2 is in the background. <br />Coal refuse placement at CWDA No. 4 commenced in 2007 with 2.514: IV slopes from the toe of <br />the refuse bank to 50 feet. Above 50 feet refuse has been placed at 3H:1V slopes. Native soils • <br />have been blended with refuse to improve workability and compaction. Bowie would like to <br />increase the storage capacity of CWDA No. 4 by increasing the ultimate height from 118 feet <br />(per the initial stability evaluation by BGI (2007)) to 150 feet. Slope angles of the refuse are <br />proposed to remain the same. <br />3.0 GEOTECNNICAL INVESTIGATION <br />Geology of the Bowie mine area in general, and the CWDA No. 4 in particular, consists of nearly <br />Flat Cretaceous sedimentary bedrock units ( Dunrud, 1989). Cretaceous Marcos Shale (Km) is <br />mapped near the bottom of the valley slope. The Manors Shale is described by Dunrud as light <br />to medium gray shale and mudstone with local, thin limestone beds. Unmapped local alluvial <br />and colluvial deposits are also referenced. The Cretaceous Rollins Sandstone (Kmvr), a fine to <br />very fine grained sandstone unit, overlies the Marcos Shale. The Rollins Sandstone outcrops <br />can be observed above the existing CWDA No. 4. The coal bearing member of the Cretaceous <br />Mesa Verde formation overlies the Rollins Sandstone. On the north side of the North Fork of <br />the Gunnison River valley, the Marcos Shale is covered with colluvial deposits originating from <br />the upslope sedimentary bedrock units. Slopes of the native ground surface at the CWDA No. 4 <br />footprint (prior to disturbance) were approximately 15 to 20 degrees. Slopes above the refuse <br />bank steepen to approximately 35 to 40 degrees. <br />BGI conducted a geotechnical drilling investigation for the CWDA No. 4 in December 2006. Two <br />boreholes, designated BG06 -08 and BG06 -09, were drilled at the refuse bank footprint to <br />• <br />Bowie No 2 Refuse Pole No 4 2009 Remed 4abilltv.aoc <br />PM*d k06 -481 -003 <br />Page 4 of 12 <br />