PERMFILE72133

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 5/12/2003
• Doc Name: Intro and Sections 1 thru 5 and 7 thru 8
• Section_Exhibit Name: Volume VII Geotechnical Studies
• Media Type: D
• Archive: No

Wf611 CNGINECIlMG $CIEN(;E & rFCHNOfOGV INC ~r~it~,
February 12, 1997 ~ ,'y~
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Jim Stover, P.E.
J.E. Stover and Associates ,,, ,=~ u~~l^ny
~I_:c~.,..,~ ;
2678 Compass Drive, Suite 101
Grand Junction, CO 81506
RE: Results of Additional Geotechnical Investigations for the Bowie No. 2 Mine Coal Mine
Waste Bank
WESTEC Project No. 97012
Dear Jim:
This letter summarizes additional drilling and testing performed at the site of the proposed coal
mine waste bank at the Bowie No. 2 Mine. The drilling and testing was performed to address
Division of Mining and Geology IDMGI concerns about material properties for the Mancos Shale
and stability of the waste bank as outlined in the Volume IV: Coal Mine Waste Bank Final
Design for the Bowie No. 2 Mine (WESTEC 1996). A summary of the investigations, updated
stability analysis, and conclusions are presented in the following sections.
SUMMARY OF INVESTIGATIONS
• On January 24, 1997 WESTEC conducted a geotechnical investigation at the site. The
program consisted of drilling two boreholes with hollow stem auger, conducting Standard
Penetration Tests (SPTs) at 5-foot intervals, collecting samples of materials, and laboratory
analysis of the samples. Laboratory analysis of the collected samples consisted of gradation
analysis, Atterberg limits, moisture content, and strength testing. The target material for the
investigation was the Mancos Shale. Borehole WBH-BO6 and WBH-B07 were completed in the
positions shown in Figure 1. Borehole WBH-BO6 is positioned in the lower region of the coal
mine waste bank. It was drilled to a total depth of 50 feet, in the sandstone colluvium. Blow
counts were obtained at 5-foot intervals and ranged from 20 blows per foot (bpf) at the top to
63 bpf near the bottom ("medium dense" to "very dense" consistency). Borehole WBH-607 was
drilled approximately 200 feet uphill from WBH-BO6. The total depth of the hole was 50 feet,
with a lithology of colluvial sandstone for approximately 30 feet, and Mancos Shale for the
remaining 20 feet. Blow counts in the colluvium ranged from 25 bpf near the top to 50 blows
for three inches at depth ("dense" to "very dense' consistency). Angering was still possible in
the Mancos Shale, and $PTS were conducted with very high blow counts ranging from 51
blows for 8 inches to 86 blows for 8 inches ("hard" consistency). No groundwater was
observed in either borehole. Borehole logs for these two holes are attached as Figure 2.
Relatively undisturbed samples were taken within the Mancos Shale by split spoon. These
samples were then laboratory tested for moisture content and for strength by direct shear test
(ASTM D3080). The samples of Mancos Shale were tested in their in-situ dry state and under
drained conditions. Results of the test indicate an estimated cohesion of 750 pounds per
square foot (psfl, and internal angle of friction of 46.7 degrees. The laboratory test summary is
• attached. This strength differs from that reported by Maxim (Maxim 1997) for the Mancos
Shale. Maxim conducted consolidated undrained (CU) triaxial tests on the Mancos Shale.
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