PERMFILE52001

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/2/2006
• Section_Exhibit Name: Exhibit 60B Subsidence Evaluation for the South of Divide Mining Area
• Media Type: D
• Archive: No

Subsidence Evaluation For
Exhibit 608 South o(Divide Mininv Area Pave 26
strain is projected to range from 0.7 to 42 percent Subsidence depressions and slope changes
will be less above the gate road pillars than above sofid coal barriers, because they are projected
to yield during mining by as much as 4 feet (Table 2).
Alo subsidence depressions or changes in stream gradient were observed in Deep Creek, located
about 1,050 feet above mined longwall panel 17 during the annual traverse in Iuly 2004
(Dunnrd 2004a)_ There was no observable change in stream gradient or in stream flow. The
depression and change in gradient were apparently sufficiently gradual, so as to not be perceived
by the author during the traverse along the trail by the stream.
11.3. i Potential for Hydraulic Connection Between Mine Workings and Surface
Aleaz the southwest comer of longwall panel E2, the Dry Fork channel encounters a short reach
where the E Seam overburden is less than 400 feet, with a minimum of 375 feel A prudent
concern is whether mining induced subsidence could establish a hydraulic connection between
the Dry Fork stream channel and the mine workings. To address this scenario, the maximum
projected height of fracturing and the maximum depth of surface cracks were considered. As
discussed in Section 5.2, the effective height of fracturing in the South of Divide mining area is
estimated to range from 9[ to 18t, or a maximum fracture height of 252 feet for a mining height
of 14 feet However, Peng (1992) states that the upper one-third of the fractured zone has only
minor fractures with little potential for water conductivity. Therefore, the height of the fractured
zone capable of transmitting water would betwo-thirds of the 18t, or 168 feet
• The maximum height of the caved zone is projected to be St, or 70 feet, for the South of Divide
mining area. When added to the effective fracture zone height of 168 feet, the combined heights
of the caved and fracture zones capable of transmitting water is projected to be a maximum of
238 feet
As discussed in Section 5.3.2, the maximum crack depth in the South of Divide mining area is
estimated W be 15 feet in terrains with slopes less than 30 percent, with depths up to 35 feet
occurring locally in steep topography. For [he Dry Fork channel neaz the western edge of
panel E2, the maximum projected crack depth is 15 feet Consequently, the combined maximum
heights of the caved and fractured zones and the maximum crack depth is 253 feet Even at the
minimum overburden thickness of 375 feet, an estimated 122 feet of unfractured bedrock will
remain in tact In addition, the presence of soft shales and claystones is the E Seam overburden
will increase the probability that the strata will warp rather than fracture during the subsidence
process.
11.4 Springs, Water-Bearing Zones, and Ground Water Wells
The Mormtain Coai Company Spring and Stock Pond Location Map for the South of Divide
shows one decreed spring (Spring 21), three springs found flowing at every site visit (in 1975,
1977, 1979, and 1980), thirty-three intemvttent springs, and two groundwater wells that are
currently monitored. Only a few springs in the West Elk Mine area indicate a source from a
local bedrock water-bearing zone. Most springs likely have sources from local water-bearing
zones in surficial material (debris flows, colluvium, and possibly alluvium}.
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