PERMFILE100540

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/13/2005
• Doc Name: 2.05.5 Post - Mining Land Uses
• Type & Sequence: PR10
• Media Type: D
• Archive: No

West Elk Mine
• Pendleton of DMG, the observed features aze typical of lazge landslide masses in the Williams Fork
Formation (geological equivalent of the Mesaverde Formation) and they occur prolifically
throughout the North Fork Valley on slopes of varying gradient and aspect. Based on his
experience in the Forth Fork Valley, Dr. Pendleton concluded that subsidence does not appeaz to be
a significant determinant in the reactivation or initiation of landslide activity. CDMG concluded
that "there is no evidence with which to definitively verify or discount a connection between
subsidence of the MCC mine workings and this active landslide."
Eight crack locations were visited during the CDMG inspection. While most of the surface cracks
were attributable to rejuvenated landslide movement, three minor cracks were reported to be the
result of mining subsidence (Nos. 2, 3, and 8 on Figure 19A). These cracks were three to four
inches wide and less than one foot deep. Field observations by MCC personnel indicated that these
cracks were already healing shortly after mining had occurred. Two of these cracks (Nos. 3 and 8)
aze typical of the dynamic subsidence process. As mining occurs, the overburden above the mined
portion subsides, and differential movement results between the mined and umnined areas. Surface
cracking can occur at the location of the differential subsidence. As mining continues, the adjacent
overburden subsides and the surface cracks will usually close completely (DeGraff and Romesburg
1981). These cracks healed significantly as evident in the late summer of 1997. Additionally, the
overburden thickness under the azeas where the cracks occurred was less than 500 feet~ne of the
few locations within the permit azea where the overburden is this shallow.
6. Within the Apache Rocks mining area Mr. Dunrud has observed several additional
surface cracks (see report titled "Subsidence Observations, West Elk Mine, July 22-24,
2003. These include the following:
• Location 13 -located in the NW 1/4 ,Section 28, T 13 S, R 90 W
• Location 3 -bluff located above the eastern part of longwall pane114, above the
eastern end of longwall pane114, in NE'/~, Section 27.
• Location 1 -located in massive sandstones of the Ohio Creek Formation, above
the approximate middle part of longwall pane114, in the NE'/., Secfion 27.
• Location 12 -located on friable sandstones of the Barren Member of the
Mesaverde Formation above the middle part of longwall panel 13, in NE'/., Section
29.
• Location 10 -located in sandstones of the Barren Member above longwall panel
13, about 2,000 feet east of location 12 in E'/:, Section 27.
7. Within the Box Canyon mining area all cracks observed were deemed to have been caused
by mass-gravity movement (lateral spreading along ridges) or by the desiccation process
(no longwall mining had occurred in this area at the last time the area was visited). These
features were observed above projected longwall mining panels 18-22 in Section 14 and
23, T 13 S, R 90 W.
Given the long and extensive history of mining in the area, it is surprising the small number of
subsidence related features that have been identified. It cannot be proved that these represent
the only cracks associated with the mine, but given the regular survey activity, inspection of
the subsidence profiles, and seasonal landowner, hunter, and U.S. Forest Service (USFS)
personnel activity, additional cracks would have been noted if they existed. This lack of
2.05-99 RevisedJime 2005 PRIO