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 29

831-032.923 Wright Water Engineers, Inc.
December 2021
10.0 POTENTIAL IMPACTS OF SUBSIDENCE AND MINE-INDUCED
SEISMIC ACTIVITY ON LANDSLIDES AND ROCKFALLS
10.1 Landslides
The landslides listed below are all naturally occurring features, which become less stable, or
become unstable and slide, during periods of increased precipitation. A review of aerial
photographs of the Apache Rocks and South of Divide mining areas, which were taken in 1963
and 2004, show that the slides listed below appeared to be more stable in 1963 than they are now.
Mr. C. Richard Dunrud (retired U.S. Geological Survey coal mine subsidence expert and author
of USGS Map C-115) observed that many of the existing landslides during periods of high
precipitation were less stable, or became unstable and moved in the mid-1980s and mid-1990s.
Landslides were identified in the Dry Fork mining area as part of the Final Environmental Impact
Statement (2005). Map 1 is a composite showing the landslides in the Southern Panels mining
area.
The landslides in the southeast side of West Flatiron and on the west side of Deep Creek in the
Apache Rocks mining area showed no visual effects when longwall mining occurred beneath the
areas. It therefore seems apparent that wet seasons affect landslides more than does longwall
mining. During very wet periods, however, landslides that are already unstable may locally be
triggered by mine subsidence.
A total of twelve landslides, landslide areas, or landslide and rockfall areas, have been mapped in
the Apache Rocks West and Southern Panels mining areas during field mapping with the U.S.
Geological Survey (USGS) in the 1980s and also during the annual subsidence observations in
these areas.
1. Apache Rocks West mining area:
a. Landslide located just north of Minnesota Reservoir in SW¼ of Section 29. Mining of
the B-seam longwall panels B12, B13, and B13-A did not have any observable effect
on the landslide.
b. Landslide area located above mined longwall panels E14 and E15 in NW¼ of Section
26. These landslides appeared to be unaffected by longwall mining beneath them.
c. Landslide area located on the west side of Deep Creek, located above the southeastern
part of mined B-seam longwall panel 17 in the NW¼ of Section 35. This landslide also
appeared to be unaffected by mining below when observed in July 2003.
2. Southern Panels mining area (Map 1):
a. An extensive landslide is located south of Minnesota Reservoir north of the projected
E-seam longwall Panels E16 and E17, in the N½ of Section 32, Township 13 South,
Range 90 West (Dunrud 1989). Minimum overburden depth to the E-seam ranges
from 360 to 600 feet. The average slope of the slide is roughly 20 percent. The
landslide contains more cracks and scarps in the upper part and more depressions and