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 of Divide Mining Area Page 32
health and safety conditions in the mine. Plans for a rapid and uniform mining rate are affected
by market demands (or -ack thereof) for a constant, high volume of coal.
16.0 SUMMARY AND CONCLUSIONS
One of the more important conclusions of this report is that all subsidence parameters (in terms
of the ratio of maximum vertical displacemendoverburden depdr compared with the ratio of
mining panel width/overburden depth) determined from the West Elk Mine subsidence
monitoring networks fall within the range of those observed during annual observations by the
author. The parameters also fall within the range of those measured and calculated in four
different coal mining areas by the author in Colorado, Utah, and Wyoming (Dunrud 1987). The
subsidence parameters also plot favorably on the appropriate rational Coal Board graphs
(Figures 4 and 5).
Results of subsidence measurement and analysis in the West Elk subsidence monitoring area also
are in general agreement with the computer modeling programs developed in the Eastern United
States. These favorable comparative results calibrated by West Elk subsidence measurements,
therefore, give added assurance that the subsidence parameters projected for the South of Divide
mining area are realistic and correct
Specific conclusions are as follows:
1. Maximum vertical displacement (subsidence), tilt, and horizontal strain predicted for the
South of Divide mining area are likely to be conservative values. Based on annual
observations of subsidence effects in the Apache Rocks mining area, maximum vertical
displacement, tilt, and strain values may be less than those projected in Section 5.3 and
Table 2. However, it is recommended that subsidence measurements be made in Dry
Fork above the western part of longwall panels E2 and E3, in order to compare predicted
results (fable 2) with field measurements.
2. Mining of the nine planned longwall mining panels in the South of Divide Mining area
will not impact Minnesota Reservoir. The reservoir is completely out of the area of
mining influence. All mine workings, including longwall panels E2, E3, and E9, are 500
to 600 feet farther away from the reservoir footprint, using even using the mast
conservative 45-degree angle of draw.
3. ro cracks are expected to occur in the alluvium in any of the drainages of the Dry Fork
of Minnesota Creek or Lick Creek. As discussed in Section 5.3.2 of this report, no cracks
have been observed during annual field visits by the author in the alluvium of drainages,
such as Deep Creek and Sylvester Gulch, when longwall mining occurred below. The
alluvium in Deep Creek and Sylvester Gulch above longwall panels 15 and 16, which
ranges from an estimated 25 to 150 feet thick beneath the stream channel, was subjected
to maximum tilt and strain, because it was within the area of influence of the eastern
boundaries of these panels.
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831-032690 Wright Water Engineers, Inc.