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 Evaluatron For
ExhibrT 608 South of Divide Mining Area

21
Minnesota Creek, the Dry Fork of Minnesota Creek and its tributaries, and in local areas along
the main fork of Lick Creek. Vertical displacement, tilt, and strain produced by mining may
locally trigger already unstable rocks to fall during, or shortly after mining.
The areas with steep slopes in the South of Divide mining area, which have the greater potential
for rockfalls, are located either in aeeas with local access roads, which have only limited travel,
or in areas remote from any access roads of other man-made features. Based on a review of
aerial photographs and analysis of the USGS 7.5-minute quadrangles, there are eight areas with
slopes ranging from 30 to 80 percent that contain local cliffs and ledges (small cliffs 5 to 10 feet
high). The seven general areas listed below (listed in an east-to-west, north-to-south direction)
have a low to high rockfall potential (Map 1):
1. Steep slopes (with an estimated rockfall potential ranging from moderate to high) located
north of Dry Fork and west of Minnesota Reservoir. However, no mining is planned in
this area, so this rockfall area would not be impacted.
2. Two steep ridges with cliffs and ledges, located above the northern part of longwall panel
E9 east of the landslide area described in Section 10.1 (mostly in the SE'b of Section 32,
Township 13 South, Range 90 West)_ There are no roads or man-made structures in the
area.
3. The south end of a steep ridge containing cliffs and ledges located north of Minnesota
. Reservoir and Dry Fork and north of the confluence of Deer Creek and Dry Fork above
the western edge (within the area of mining influence) of un-mined longwall panels El
and E2 (Sl/2, Section 29 and the NW'b of Section 33, Township 13 South, Range 90
West). The Dry Fork road is located 400 to 500 feet south of the nearest area boundary.
4. A steep to moderately steep slope containing eight separate rockfall areas, located north
and south of Dry Fork and its tnbutaries. The estimated rockfall potential is low to
moderate. The rockfall areas are located above longwall panels EI through E4 (Sections
33 and 34 and the NE %: of Section 35, Township 13 South, Range 90 West).
5. The area is located in the southwestern part of the South of Divide mining area east of the
main fork of Minnesota Creek. While the majority of this area is located outside the
influence of mining, the northeastern part of this area, which has an estimated moderate
to high rockfall potential, is within the area of mining influence of the western and
southern part of un-mined longwall panels E8 and E9, respeMively (located mostly in the
W'/: and S''/s, Section 5, Township 14 South, Range 90 West).
6. This area contains six rockfall areas that have locally steep ridges. The area is located
neaz the headwaters of Deer Creek, Poison Creek, Lick Creek, and a tributary of Dry
Fork. The areas, which have an estimated low to moderate rockfall potential, are located
above, or partly within, the area of mining influence of un-mined longwall panels ES
through E8 (located in parts of Sections 3, 4, 9, and 10, Township 14 South, Range 90
West).

831-032.690 WdghtWaterEngineers, tnc.