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• <br />• <br />• <br />at 10 foot intervals thereafter. When competent bedrock material was encountered in <br />Boreholes WBH -84 and -65, the drilling switched from auger to mud rotary using a 4-inch <br />diameter tricone bit. During rotary drilling, cuttings were logged for consistency. Each <br />borehole was drilled to the competent Mancos shales. Boreholes WBH-64 and -B5 were each <br />taken to approximately 55 feet in depth, both extending 22 feet below the shale interface. <br />Appendix A shows the log for these Boreholes, and Drawing 95266-03 shows the geologic <br />cross section in its existing condition. The drilling confirmed a downward trending Mancos <br />shale contact with a 10- to 20-foot layer of colluvial sandstone over the shale. At the <br />competent Mancos contact, SPT split spoon drives penetrated less than 6 inches. Recovered <br />split spoon drive material was dry, very dense, and hard. SPT blow counts within the colluvial <br />sandstone indicated amoderate-strength material, which was also dry. Toward the old coal <br />loading area, Till material above the colluvium increases in depth. This fill material is <br />characterized by low SPT blow counts, indicating a low strength, loose material. <br />In Boreholes WBH-B4 and -B5, where the mud-rotary bit was used, water was needed to <br />circulate cuttings to the ground surface for sampling and logging. Groundwater depth in these <br />holes could not be directly measured. A 1.5-inch PVC piezometer was installed in Borehole <br />WBH-84 to measure the groundwater after drilling-related water had dissipated and the <br />conditions had stabilized. The total depth of the piezometer was 54 feet below the ground <br />surface Ibgsl, and screened to 24 feet bgs. The annulus was filled with high permeability <br />sand, and a bentonite cap was installed above the screen. Several weeks after installation, <br />on November 11, the piezometer reading indicated a water level at 27 feet bgs. Since <br />Borehole WBH-B3 was drilled to 30 feet with no groundwater encountered, the water level <br />within the piezometer still likely reflects the drilling water and not stabilized groundwater <br />conditions. <br />96266/1424.RPT Coel Mine Weste Benk Final Design for the Bowie No. 2 Mine <br />June 1996 W E S 7 E C <br />11nfgUACY-Ol <br />4 <br />