PERMFILE53387

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 69 Section A I. Initial Project Description
• Media Type: D
• Archive: Yes

Mountain Coal Company Exhibit 69
West Elk Mine Slope Stability Improvements
•
Sylvester Gulch Substation Site
Sylvester Gulch Facilities Area
Introduction
Mountain Coal Company, LLC (MCC) proposes to improve the global slope stability of
the Sylvester Gulch Substation site by constructing 24 trench drains on the slope above
the substation. Should these trench drains prove ineffective in improving the local
stability of the Landing #2 light-use road, a retaining wall will be constructed along the
outside edge of the Landing #2 light-use road above the substation. Figures 1 through 4
show the location and details of the trench drains and the retaining wall.
As previously reported to the Division during the construction of the Sylvester Gulch
Facilities Area (and as discussed during subsequent field inspections), the slopes above
the substation and below the Landing #2 light-use road have experienced s-ow, sliding
type movements since first constructed in the summer of 1997. In an effort to control the
.~ immediate movement, MCC completed slope grading, constructed benches, and installed
a large french drain. MCC has monitored these slopes with both surface surveys and
inclinometers. The data showed that the slopes were essentially stable over the fall and
winter of 1997, but additional movement of the slide mass occurred during spring 1998.
The head scarp advanced approximately 30 feet closer to the Landing #2 light-use road.
The head scarp was again stable and movement within the slide mass decreased in the fall
1998 to very slow rates; however, MCC expects some increased movement during the
spring of 1999. Therefore, with the assistance of its consultant, Barr Engineering, MCC
has completed these two stabilization designs, and both will be constructed, if necessary,
for long-term stability. These include trench drains and a retaining wall, as described
below.
Trench Drains
MCC proposes to install 24 trench drains on the slope above the Sylvester Gulch
Substation, and below the retaining wall discussed above. The locations of the drains are
shown on Figure 3. The drains vary in length from 85 feet to 155 feet. The maximum
depth of the drains will be 20 feet and the bottom width will be 3 feet. The trenches will
be backfilled with '/<-inch washed rock and 12-inch riprap. A detailed cross-section of
the drains is shown on Figure 4. The drains will daylight above the rock outcrop to the
north of the substation pad and free drain down the rock face and into the existing
sediment ditch. Approximately two feet of native clay soils will be compacted over the
.. trenches to minimize the amount of surface water entering the drains. The entire slope
will be regraded and compacted to achieve flatter slopes, to eliminate slope cracks, and
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