PERMFILE130419

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2005
• Section_Exhibit Name: Exhibit 60C Subsidence Evaluation 2004 Geological Hazard Field Observations for the WFLA
• Media Type: D
• Archive: Yes

Exhibit 60C
Subsidence Evaluation and 2004 Geologic Hazard Field Observations
West Flatiron Lease Area
•
TABLE 1
Maximum Subsidence Parameters For
West Flatiron Lease Area t'i

Parameter Panel 18A (t=12ft) Panels 18-19 (to12 it) tsl Panels 20-21 (to12ft)
W /d: Max
Min 18A 690/600 = 1.15
690/1310 0.53 18 970 / 750 =
970 /1700 = 1.29
0.58 20 970 / 1030
970 / 2250 = 0.94
0.43
Max
Min 19 970 / 910
970 / 2250 1.07
0.43 21 970 / 1300
970 / 2175 = 0.75
0.45
S°o=a~•tt4l
(a°o=S~dt) 1.7 to3.8ft
(0.14 to 0.32) 2.2 to6.5ft
(0.18 to 0.54) 2.9 to6.5ft
(0.24 to 0.54)
Sm=e•ttsl
(a = S„~t) 6.0 to 9.6
(0.5 to 0.8) 4.S t09.6ft
(0.4 to 0.8) 4.8 t09.Oft
(0.4 to 0.75)
Sm/d lel (0.005 to 0.016) (0.0021 to 0.013) (0.0021 to 0.009)
Mm (2.2 to 3.0 S„Jd) n1 0.011 t0 0.048 0.005 t0 0.039 0.005 l0 0.027
Em (in terms of S„Jd) Isl
(1.3 to 1.5 S„Jd) 0.006 to 0.024 0.003 to 0.020 0.003 to 0.014
-Em (in terms of Sm/d) Isl -0.006 to -0.038 -0.003 to -0.031 -0.003 to -0.022
Maximum Crack 1 5- 15 ft 5- 20 ft 5- 15 ft
Deptht9t 2 10-20ft 10-35ft 10-20ft
Break Angle 1101 0 - 5° 0 - 5° 0 - 5°
Angle of Draw tf0~ 10 - 20° 10.20° 10 - 20°
~'~ Maximum subsidence parameters include the total length of mining panels 18-21, and therefore include the Box
Canyon mining area as well as the West Flatiron Lease area; t is the average coal extraction thickness (12 ft), which
may be more or less than this average.
tzl Maximum vertical displacement, tilt, and horizontal strain apply to ground surfaces with slopes less that 30%;
values may be higher on slopes greater that 30 percent.
13lAll longwall panels are numbered according to their planned panel identification.
I`t Subsidence and subsidence factor above gate road (chain) pillars.
fs1 Maximum vertical displacement (subsidence) range above the longwall panel centers, based on the average
planned coal extraction thickness of 12 feet, is obtained from Figure 4, Exhibit 60B.
tel Ratio of the range of maximum vertical displacement to overburden depth range for the five projected longwall
panels. Minimum overburden tlepth to the B seam is located in the Raven Gulch tributary in the West Flatiron lease
area above the projected centerlines of longwall panels 18 through 21. Minimum overburden depth of the projected
centerline of longwall panel 18A (600 feet) is located 300 feet west of the east West Flatiron Lease boundary.
nl Maximum range of tilt values, in terms of Sm/d, is obtained from Figure 1.
Isl Maximum range of positive and negative horizontal strain in terms of Sm/d is obtained from Figure 1.
191 Maximum crack depth (in feet) in bedrock that is estimated to locally occur near cliffs, ledges, or steep slopes on
either side of West Flatiron. The first depth range (1) is for bedrock sloping less than or equal to 30 percent. The
second depth range (2) is for steep bedrock sloping more than 30 percent and cliffs. No cracks are predicted to
occur in alluvium. No cracks are predicted to occur at the surface of colluvium thicker than about 10 feet
• t10~ Predicted range of break angle and angle of draw, measured from a vertical reference.
831-032.650 Wright Water Engineers, Inc. Page 11
November 2004