2010-03-23_REPORT - C1980007

• Permit No: C1980007
• IBM Index Class Name: REPORT
• Doc Date: 3/23/2010
• Doc Name: Fall 2008 Subsidence Report Review Memo
• From: DRMS
• To: File
• Permit Index Doc Type: Subsidence Report
• Email Name: TAK
• Media Type: D
• Archive: No

renewable resource lands
or structures
Item
Vertical
subsidence
magnitude
Horizontal
displacement
magnitude
Angle of draw
USFS roads
USFS ponds
Predicted impact
in permit
Maximum 18.4 ft.
in two-seam mining
areas. Less than 1
ft. near panel edges
in single-seam
mining areas.
Maximum
horizontal strain of
3.9%
8 - 21 degrees
Rockfalls, cracking
Draining
Observed impact
Between 2000 and 2007 visual
observations are used for verifying
the conceptual subsidence model,
rather than quantitative monitoring.
The Spring 2009 report and previous
reports include data from pre-
mining surveys of panel E-1 and the
thalweg of the Dry Fork of
Minnesota Creek. Postmining
surveys will be conducted after Panel
E-1 and the Dry Fork are
undermined.
USFS light use roads have been
undermined by the east end of Panel
E-1 since the previous report (Fall
2008). Other than significant
slabbing of the cliff face next to the
West Flatiron road, no new rockfalls
or cracking were found resulting
from previous undermining. (The
West Flatiron site was examined
during the OSM subsidence special
focus oversight inspection in July
2009.)
No new undermining of USFS ponds
since previous report (Fall 2008).
No new draining observed from
Prediction accurate?
Although subsidence
displacements have not been
surveyed since 1999, visual.
observations described in the
Spring 2009 report indicate
subsidence displacements and
the angle of draw have probably
not significantly exceeded the
predicted values. The Spring
2009 report contains prem ring
and postmining elevations
monitored in Sylvester Gulch;
these data indicate no significant
subsidence of the land surface.
Yes
Yes
2