Laserfiche WebLink
• The boreholes were drilled with a Dietrich D50 track-mounted drill rig using a 4'/a-inch solid <br />stem continuous flight auger. Soil samples were obtained using atwo-inch I.D. split-spoon <br />"California" sampler. Standard penetration tests (SPT) were conducted in general accordance <br />with ASTM D 1586 to characterize the consistency of the foundation soils. The recovered soils <br />were logged by a geotechnical engineer, and representative samples of subsurface materials <br />encountered were brought back to our laboratory for detailed examination and testing. Open <br />standpipe piezometers were installed in each borehole. <br />Native soils at the Gob Pile No. 3 footprint consist of colluvial and alluvial materials originating <br />from sedimentary units and colluvial slope wash deposits on the slopes to the northwest. In <br />general, subsurface soils encountered during drilling consisted of damp to moist, stiff to hard, <br />silty clay with variable gravel and cobble content to clayey gravel and cobbles. Some sandy <br />lenses and layers were encountered, as well as occasional boulders. Overall, the soils were quite <br />heterogeneous as may be expected for alluvial and colluvial deposits. Increased cobble and <br />boulder content was observed in three of the boreholes at depths of 40 to 70 feet. The driller had <br />difficulty cleaning auger cuttings out of some of the boreholes at depth, thereby making soil <br />sampling difficult. <br />The boreholes were drilled to total depths ranging from 40 to 90 feet. No definitive evidence of <br />bedrock was encountered in any of the boreholes to these depths. However, in borehole BG06- <br />02, located at the northwestern portion of the gob pile footprint, the driller noted that shale <br />bedrock was possibly encountered at an approximate depth of 83 feet. Due to slough in the <br />borehole, we were unable to verify shale bedrock at this depth with the available drilling tools. <br />Open standpipe piezometers were installed in each of the boreholes. The depth and screened <br />interval of the piezometers was varied to characterize groundwater conditions at various depths. <br />Groundwater levels were measured during drilling and twice subsequent to completion of <br />drilling. Table 2 presents groundwater monitoring at the Gob Pile No. 3 footprint to date. <br />Table 2. Summary of Groundwater Monitoring <br /> Piezometer Construction <br /> Total Depth Screened Interval Depth to Groundwater <br />Borehole ID (ft) (ft) 12/1?J06 1!31/07 <br />BG06-01 58 48-58 Dry to T.D. 57.5 <br />BG06-02 29 19-29 19.1 19.0 <br />BG06-03 50 40-50 39.3 33.9 <br />BG06-04 40 30-40 36.9 27.0 <br />BG06-05 18 8-16 Dry to T.D. Dry to T.D. <br />8G06-06 28 18-28 Dry to T.D. Dry to T.D. <br />BG06-07 28 18-28 Dry to T.D. Dry to T.D. <br />3.2 Gob Pile No. 2 <br />Boreholes BG06-10, BG06-1 t, and BG06-12 were drilled within gob at Gob Pile No. 2. The <br />boreholes were drilled primarily to obtain thin-walled (Shelby) tube samples, therefore few <br />• standard penetration tests were conducted. In general, gob consisted of moist, very stiff, clayey <br />gravel to gravelly clay with variable sand, cobble and boulder content. The boreholes were <br />Bowie Gob Pile No. 3 stability report <br />Project 1106-481 A02 <br />Page fi of 17 <br />