2009-10-30_PERMIT FILE - C1982056 ‎(6)‎

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 10/30/2009
• Doc Name: WESTERN MINING DISTRICT
• Section_Exhibit Name: Exhibit 25Z WMD Subsidence Review
• Media Type: D
• Archive: No

SubTerra, Inc. Twentymile Coal Company 04/07/09
Foidel Creek Mine
( Permit Revision PR09 -08 Subsidence Evaluation
3. Subsidence over the rigid -yield pillars separating adjacent longwall panels was
estimated using the data from the original Fish Creek study area (SubTerra, 1999) and
data gathered during mining Panels 9, 8, and 7 -Right in the Eastern mining district and
Panel; 19 -Right in the Northern Mining District. A comparison of the predicted and
actual subsidence from 12 and 13 -Right was also made using data collected when 12
and then 13 -Right undermined the Energy Spur track.
4. The Start Room profiles for all panels were estimated using data from monitoring lines
1000 and 3000 in the Fish Creek study area (SubTerra, 1999). These data are
contained in the semi - annual reports and in prior permit submittals.
Subsidence predictions were made for overburden thickness of 1,100 and 1,400 ft representing the
range of conditions in the study area. The results of these predictions are contained in Figures 2
and 3. Summary data include:
• Maximum subsidence of 60 and 69 inches for overburden thickness of 1,400 and 1,100
ft, respectively.
• Up -dip and down -dip draw angles of 12 and 21 respectively, which define the limits of
subsidence.
• Maximum surface strains less than -0.004 (compression) and +0.005 (extension).
As noted above, TCC has developed an extensive subsidence database from monitoring lines
positioned to measure start, transverse, and traveling subsidence profiles. No further systematic
subsidence data gathering is therefore warranted under this permit.
I 3. Evaluation of Impacts to Routt County Road 27
As shown on Drawing 3, Routt County Road 27 crosses the western half of five of the six longwall
panels (13L through 17L) and will therefore be subject to subsidence on five separate occasions as
each longwall panel passes underneath. It is estimated that Panel 17 -Left will initially subject the
road to up to 5 -ft of subsidence. Predicted gradient change, after the completion of the five
longwalls, is shown in Table 1.
Prior experience has indicated that strains up to 0.005 (in /in) caused cracking in the road surface
that required cold patching. This phenomenon is more likely to occur over the southernmost
panels, however may occur in sections of the road that overlay all the panels. Just over one mile
of road may be affected.
4. Evaluation of Impacts to Fish Creek and Its (AVF)
Fish Creek meanders northwards across its Alluvial Valley floor and passes over the Western Mining
District starting from a location above the sub mains adjacent to 15 -Left (Drawings 2 and 3). From the
sub - mains, it flows north and then south across 15 -Left, south across 14 -Left then eastwards above
the rigid -yield pillar pair separating 14 -Left and 13 -Left. Fish Creek eventually leaves the planned
mining area beyond the recovery room for 14 -Left.
t
2 PN: 2009 -04