2013-02-11_PERMIT FILE - C1996083 ‎(2)‎

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 2/11/2013
• Doc Name: 11/20/2012 Buckhorn Geotech Report TR-75 As Built Stability Analysis
• Section_Exhibit Name: Volume IX Coal Mine Waste Disposal Area No. 2
• Media Type: D
• Archive: No

BUCKHOR EEOTECH
Civil, Structural & Geotechnical Engineers
November 20, 2102
Tamme Bishop, PE
JE Stover & Associates
23532 North 7" ST., Unit B
Grand Junction, CO 81501
RE: BOWIE# 2 MINE, CWDA PILE #4
SUBJ: RESPONSE TO DRMS COMMENTS
Dear Tamme:
222 South Park Ave. • Montrose, CO 81401
Ph.: (970) 249 -6828 • FAX: [phone]
Per your recent request, we have re- analyzed the Bowie Mine Coal Waste Disposal Area
(CWDA) #4 for slope stability based on the comments provided by the DRMS in their review
of the TR -75 application dated October 26, 2012. Based on those comments, we have
performed several analyses in SLIDE (version 5.0) to confirm the minimum slope required to
achieve a factor of safety of greater than 1.5 for the as -built conditions.
Assumptions for As -Built Stability Analysis
• Horizontal segments of steep slope (2.0 H: IV) ranged from 50 to 130 feet to match
DRMS measured segments highlighted in green -blue in their letter.
• Material properties are the same as originally modeled in our 2009 stability analysis
• No phreatic surface was modeled in the as -built model since the pile is no longer
receiving wet gob and, as demonstrated by the on -going monitoring results of the
adjacent CWDA pile #2, the coal waste dewaters over time and will eventually have
no phreatic surface associated with it.
Model Results
The minimum global factor of safety (F.S.) for the as -built configuration of CWDA #4 at the
Bowie #2 Mine was determined to be 1.536 using the Bishop simplified method used for
analysis. To confirm this calculation, the slope was also analyzed using three other methods
as indicated in Table 1.0.
Table 1.0 Analyses Methods and Results from SLIDE modelinq
Method
Minimum
Factor of
Safe
Slope
(H:V)
Comments
Janbu Simplified
1.537
2.0:1
Bishop Simplified
1.536
2.0:1
Global minimum
Spencer
1.537
2.0:1
GLE /Mor enstern -Price
1.537
2.0:1
The results in Table 1.0 indicate that all four methods produced a resulting global minimum
factor of safety of at least 1.536 for the as -built slope. Since all of the factors of safety are
Bowie Mine #2 — CWDA Pile # 4
DRMS Response Analysis
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