REP48888

• Permit No: C1982056
• IBM Index Class Name: Report
• Doc Date: 12/15/2004
• Doc Name: 1st Half 2004 Subsidence Report Review Letter
• From: DMG
• To: Twentymile Coal Company
• Permit Index Doc Type: Subsidence Report
• Media Type: D
• Archive: No

Predicted impact
Item in permit Observed impact Prediction accurate?
a lication
The stations ranged from M404
through M430 during the report
period. Initially, a maximum of
76.16 inches was reported at
station M414. 63 inches were
anticipated (a 30% deviation). In
addition, substantial deviations

" (approximately 100%) are The operator was asked to
of
Maximum 67 indicated between stations 422 clarify the findings of this

Vertical subsidence at the and 430. The revised report
section of the initial report. A

subsidence mid-panel station indicated a 76.16 maximum
comparison of predicted vs.

magnitude 428 [Table 1 of subsidence at this same station.
measured subsidence, both
Exhibit 4e-3 of Corrections resolved the initial and corrected, is
permit] questions between stations 422 attached.
and 430. Offset, the maximum
predicted subsidence in panel 15
was 66 inches; actual maximum
was 76 inches, 10 inches or 15%.
The maximum predicted
subsidence in panel 16 was 67
inches; actual was 78 inches, 1 I
inches or 16%.
Horizontal Magnitudes are reported.
displacement No magnitudes Usually in the O.Ox range but up N/A
magnitude Predicted to a couple of feet reported in the
trou hs.
Maximum 21
degrees [page 2 Reported as ranging between 17.5
Angle of draw of Exhibit 4e-3 and 19.5 degrees. Yes.
in permit
a lication].
Continued undermining; no
Twentymile No off-site impact based on data from Yes.
Sandstone impacts monitoring wells (in annual
hydrolo re orts).
UP Railroad
track. Track will be The track subsided as predicted.
Monitoring subsided. (p. Track was successfully re- Yes.
within 500 feet 2.05-181.6 of leveled.
and 1500 feet permit)
beyond
Yampa Valley
Electric None. None.
Association
owerline