2014-06-19_PERMIT FILE - C1981019A

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 6/19/2014
• Doc Name: Geotechnical Stability Report For Highwall Mining At the Colowyo Coal Mine
• Section_Exhibit Name: Exhibit 23, Item 1
• Media Type: D
• Archive: Yes

July 23, 2013 Page 4
Isopachs of seam floor elevation, thickness, overburden, and interburden, for the target
seams are shown in Figures 2 through 25. Summaries of seam characteristics for the target
seams in the South Taylor and West Pits are presented in Tables 1 and 2, respectively. The
South Taylor highwall miner openings will dip down between approximately 2 and 7 degrees
(possible end wall mining at the south end of the pit will be along strike, with seam sidedips
nearing 9 degrees; possible end wall mining of the G7 Seam at the north end of the pit will be
downdip at less than 2 degrees). West Pit highwall miner openings will dip up between
approximately 2 and 5 degrees, although portions of the C Seam study area have dips up to
9 degrees.
Table 1. Characteristics of the Target Seams in the South Taylor Pit
Parameter Value
G78 Cover 60 to 510
G7 Thickness (north of 3 -ft parting line) 6.5 to 10.5
G78 Thickness (south of 3 -ft parting line, including parting) 15 to 21
G78 to E Interburden 175 to 290
E Cover 40 to 285
E Thickness (north of 3 -ft parting line) 8 to 11.5
D2 /E Thickness (south of 3 -ft parting line, including parting) 13.5 to 18.5
Table 2. Characteristics of the Target Seams in the West Pit
Parameter
Value
(ft)
F Cover
F Thickness
160 to 460
4.5 to 13
F -E Interburden
15 to 30
E Cover
E Thickness
220 to 440
6.5 to 7.5
E to D2 Interburden
15 to 45
D2 Cover
D2 Thickness
200 to 320
1.5* to 7 ft
D2 to C Interburden
25 to 75
C Cover
C Thickness
100 to 240
2* to 6
*Minimum mining height of the ADDCAR "mid- seam" miner is 3 ft
It should be noted that in Figures 2 through 25, the solid rectangle indicates the extent of
potential highwall mining as defined by the pit face identified by Colowyo, and a 1,400 -ft
penetration distance. This distance represents an upper limit penetration target based on past
experience. Actual penetration distance is likely to be lower, based on seam thickness,
undulation, and other factors. Where shown, the gray line within these rectangles represents the
penetration targets developed by Colowyo for preliminary planning purposes. The design curves
presented later in this report include the range of mining heights and cover depths within the
areas defined by the 1,400 ft penetration distance in order to provide Colowyo flexibility in
planning.
Agapito Associates, Inc.