PERMFILE41593

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 5/21/2004
• Section_Exhibit Name: Exhibit 07e-6 AVF Subsidence Study Final Report
• Media Type: D
• Archive: No

SubTerra, Inc. Twentymile Coal Company 05128103
PR6 AVF Subsidence Evaluation
• 3. Subsidence over the rigid-yield pillars separating adjacent longwall panels was
estimated using the data from monitoring line 4000 in the Fish Creek study area
(panels 1LLW and 2LLW) and data gathered during mining Panels 9, 8, and 7-Right
in the eastern 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. Figure 2 shows that maximum subsidence
was within a few inches of predicted values but the "hump" that develops over the
rigid-yield pillars separating adjacent longwall panels was broader than anticipated.
4. The Start Room profiles for Panels 18 and 19-Right (see Figure 3) were estimated
using data from monitoring lines 1000 and 3000 in the Fish Creek study area (panels
1 LLW and 2LLW). 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 4 and 5. Figure 6 also shows the predicted cumulative effects of extracting Panels 12
through 18-Right for the shallower overburden condition, which is representative of the
conditions at the eastern end of the longwall panels. Summary data include:
• Maximum subsidence of 60 and 67 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 surtace 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.
3. Evaluation of Impacts to Fish Creek and Its (AVF1
Fish Creek meanders eastwards across its alluvial valley floor and passes over the NMD starting
from a location above the north mains (Drawing 1). From the north mains, it flows along the
centerline of Panel 13-Right turning north-east at the mid-point (between panel start and recovery
rooms) of Panel 13-Right and flows north-eastwards over Panels 14, 15, 16, and 17, and
eventually leaves the planned mining area beyond 18-Right and just behind the start room for 19-
Right.
3.1 Scope of Work
The scope of work covered by this section of the report involves an evaluation of potential impacts
that may result from lowering the Fish Creek AVF during coal extraction in the Northern Mining
District. The following issues were investigated and resolved:
1. Will subsidence cause Fish Creek to overtop its existing high bank(s)?
2. If overtopping is likely, what remedial measures are required?
3. What will be the time phased increase in [he surface area of Fish Creek due to
subsidence, and/or how much of the Fish Creek AVF will be flooded?
PN: 2002-06