APPCOR10836

• Permit No: C1996083
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/19/1997
• Doc Name: BOWIE RESOURCES LTDS RESPONSE TO GEOTECHNICAL COMMENT MEMORANDA OF JAN291997-FIFTH SUPPLEMENTAL
• From: DMG
• To: DAVE BERRY
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources

1313 Sherman SI., Room 215 ~
Denver, Colorado 80203 I~~
Phone: (303) 8h6~35h7
FAX. [phone]
DEPARTMEN'T' OF
NATURAL
RESOURCE.'
DATE: February 19, 1997
Roy Romer
Governor

TO: Dave Berry lames S. Lochhead
Executive Director
Michael B. Long

FROM: Jim Pendleton Division Director
RE: Bowie Re urces Lt Response to Geotechnical Comment
Memoran a of J ry 29, 1997 -Fifth Supplemental Response -
Dated February 13, 1997 (Permit No: C-96-083)
I have reviewed the response letter submitted by James Stover, P.E. of J.E. Stover &
Associates, representing Bowie Resources, Ltd. With this letter Mr. Stover submits an additional
analysis of the proposed gob pile's stability, prepared by WESTEC. This analysis responds to
the geotechnical adequacy question contained in my memorandum of January 29, 1997.
'Geotechnical Laboratory Testing, Proposed Gob Pile" (Memo #2)
WESTEC mobilized a drill rig to drill two additional test borings within the footprint of the
proposed waste pile. Samples of the Mancos Shale were collected and analyzed in WESTEC's
laboratory. WESTEC's simple shear tests, performed under unsaturated conditions determined
the Mancos Shale at this location to exhibit an angle of internal friction of 46.7 degrees with an
estimated cohesion of 750 psf. WESTEC theorizes that MAXIM's earlier MANGOS Shale
testing, which resulted in much lower strength results, was performed under undrained/saturated
conditions. WESTEC believes that MAXIM's chosen analytical conditions are unrepresentative
of the conditions which will exist within the proposed waste pile. Using its strength
determinations, WESTEC repeated its stability analyses of the proposed waste pile. This
revised stability analysis determined the pile to have a static safety factor of 2.7 and a
pseudostatic safety factor of 2.0. As such the pile satisfies the requirements of our regulations.
In my opinion, this revised sample testing and stability analysis has satisfied my earlier
geotechnical concerns. I recommend approval of the waste pile design, as supported by this
revised stability analysis.