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• It is our understanding that borrow activities will continue up to and during gob placement at <br />Gob Pile No. 4. It is anticipated that native soils will be excavated from the slope as the gob <br />platform rises. This will provide material for subsoil cover, provide soil to blend with the gob, <br />and will increase the gob pile capacity. We recommend the excavations into the native soil be <br />benched into the slope as described in this report to maintain adequate short-term stability of the <br />excavation slope and to improve stability of the gob pile along the native soil contact. <br />We understand that foundation underdrains and surface water diversion channels will be <br />designed by others to drain the shallow foundation soils and direct surface water off, around, and <br />away from the gob pile. <br />2.3 Geology <br />According to Dunrud (1989), geology of the Bowie mine area in general, and the Gob Pile No. 4 <br />in particular consists of nearly flat Cretaceous sedimentary bedrock units. Cretaceous Mancos <br />Shale (ICm) is mapped near the bottom of the valley slope. The Mancos Shale is described by <br />Dunnrd as light to medium gray shale and mudstone with local, thin limestone beds. Unmapped <br />local alluvial and colluvial deposits are also referenced. The Cretaceous Rollins Sandstone <br />(Krttvr), a fine to very fine grained sandstone unit, overlies the Mancos Shale. The Rollins <br />Sandstone outcrops can be observed above the existing Gob Pile No. 2 and proposed Gob Pile <br />No. 4. The coal bearing member of the Cretaceous Mesa Verde formation overlies the Rollins <br />Sandstone. On the north side of the North Fork of the Gunnison River valley, the Mancos Shale <br />• is covered with colluvial deposits originating from the upslope sedimentary bedrock units. <br />3.0 SITE INVESTIGATION <br />A geotechnical drilling investigation has been conducted by BGI for the proposed Gob Pile <br />No. 4. Two boreholes were drilled at the Gob Pile No. 4 footprint to chazacterize the foundation <br />conditions. Three boreholes were drilled within gob at Gob Pile No. 2 for sampling and strength <br />testing of the compacted gob material. The findings of our geotechnical investigation are <br />discussed in this section. <br />3.1 Drilling Program <br />Two boreholes, designated BG06-08 and BG06-09, were drilled at the Gob Pile No. 4 foundation <br />footprint in December 2006. Three boreholes, designated BG06-10 through BG06-12, were <br />drilled within gob at Gob Pile No. 2, with the intent to obtain thin-walled Shelby tube samples <br />for strength testing. <br />The boreholes were drilled with a Simco 2800 H.S. truck-mounted drill rig. The boreholes at the <br />Gob Pile No. 4 footprint were drilled with a 4'/a-inch solid stem continuous flight auger, while <br />boreholes in gob at Gob Pile No. 2 were drilled with 3'/<-inch ID hollow stem augers. Soil <br />samples were generally obtained at using standard split spoon and split-spoon "California" <br />samplers. Standard penetration tests (SPT) were conducted in general accordance with ASTM <br />D 1586 to characterize the density or consistency of the subsurface materials. The recovered soil <br />Bowie Gob Pile No. 4 stability report <br />Project #OS-126-GEO <br />Page 6 of IS <br />