2022-09-29_PERMIT FILE - C1980007 ‎(5)‎

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 9/29/2022
• Doc Name: SUBSIDENCE EVALUATION
• Section_Exhibit Name: Exhibit 60E Subsidence Evaluation for the South of Divide and Dry Fork Mining Areas
• Media Type: D
• Archive: No

Subsidence Evaluation for the
Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 32

831-032.923 Wright Water Engineers, Inc.
December 2021
review of aerial photographs and analysis of the USGS 7.5-minute quadrangles, there are areas
with slopes ranging from 30 to 80 percent that contain local cliffs and ledges (small cliffs 5 to 10
feet high). The 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 Panels
E16 and E17 east of the landslide area described in Section 10.1 (mostly in the SE¼ 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 longwall panels E1 and E2 (S1/2,
Section 29 and the NW¼ 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. Following mining
in these longwall panels, no additional rockfall was observed during semi-annual field
studies.
4. A steep to moderately steep slope containing eight separate rockfall areas, located north
and south of Dry Fork and its tributaries. The estimated rockfall potential is low to
moderate. The rockfall areas are located above longwall panels E1 to E4 (Sections 33 and
34 and the NE½ of Section 35, Township 13 South, Range 90 West). Following mining in
these longwall panels, no additional rockfall was observed during semi-annual field
studies.
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 part of longwall
panels E14 and E15 (located mostly in the W½ and S½, Section 5, Township 14 South,
Range 90 West).
6. This area contains six rockfall areas that have locally steep ridges. The area is located near
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 longwall panels E5 to E8, and SS1 (located
in parts of Sections 3, 4, 9, and 10, Township 14 South, Range 90 West).
7. This area contains three rockfall areas that have an estimated low to high rockfall potential.
It is located in the Lick Creek area and above, or partly within, the area of mining influence
of longwall panels E14 and SS1 to SS4 (located in parts of Sections 8, 9, and 16, Township
14 South, Range 90 West).