2009-09-14_REVISION - C1980007 ‎(5)‎

• Permit No: C1980007
• IBM Index Class Name: REVISION
• Doc Date: 9/14/2009
• Doc Name: Email Regarding Review Memo
• From: Marcia Talvitie
• To: Tom Kaldenbach
• Type & Sequence: TR118
• Email Name: TAK
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Roan 215
COLOR-ADO
Denver, Colorado 80203 p
o N
Phone: [phone] RECLAMATION
FAX: [phone] MINING
SAFETY
INTEROFFICE MEMORANDUM Bill Ritter, Jr.
Governor
Harris D. Sherman
Executive Direclor
Date: 14 September 2009 Ronald W. Cattany
Division Director
Natural
Resource Trustee
To: Tom Kaldenbach, Lead Specialist
From: Marcia L. Talvitie, P.E. y2lC4GC?'
Subject: Permit No. C-1984-007 - West Elk Mine
TR 118 - Coal Preparation Plant and Coal Handling Facilities
Adequacy Review - Geotechnical
At your request, I have reviewed the application submitted by Mountain Coal Company for TR-
118, including the Stability Analysis of the Lower Refuse Pile prepared by Barr Engineering
Company and dated 8 September 2009.
1. The September analysis incorporates material strength parameter data reported in Exhibit 51
of the permit application package. I reviewed Exhibit 51, including Table 6, which is
duplicated in the current Barr report. Dry Unit Weights and cohesion values derived for
Colluvial Soils are variable, and Barr has taken average values to use as inputs for the
SLOPE/W stability program. Because of the potential variability, it would be wise to re-run
the analyses using a lower, more conservative cohesion value (for example, 300 or 0 rather
than 886 pso for Colluvial Soils. Please review the assumptions made regarding the
cohesion value for Colluvial Soils, and re-run the stability program to verify that colluvial
soils with lower cohesion values will not adversely affect the overall stability of the Lower
Refuse Pile with the addition of the proposed Preparation Plant Facility.
2. The Exhibit 51 Table 6 samples analyzed for Coal Waste were obtained from temporary
waste piles, and were tested prior to actual construction of the Lower Refuse Pile (LRP). Dry
unit weights ranged from as low as 45 pcf (lighter than water) to 121 pcf. Barr's analysis
averages these values, and assumes the unit weight of coal refuse in the LRP to be 91.9 pcf.
A better source of accurate data on the unit weight of coal refuse can be found in the
quarterly waste pile reports submitted during the construction of the LRP between 1988 and
1990. Coal refuse in the lower portions of the LRP apparently ranged between 84 and 115
pcf, while unit weights in the upper portions ranged from 108 to 124 pcf. Overall, a moist
unit weight of 110 pcf may be more representative of the coal refuse. This value is
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