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 OSI28I03
PR6 AVF Subsidence Evaluation
• Several assumptions were made to simplify the analysis:
Fish Creek elevation will rise, relative to the surrounding ground, a distance equal to
predicted ground subsidence at that point.
The effects of spring run-off on creek elevation would be in addition to the effects of
subsidence.
3.2Aaproach
Our approach involved superimposing estimated subsidence on over 100,000 data points
representing Fish Creek and the immediate high bank adjacent to Fish Creek and comparing the
subsided elevations with existing (i.e., un-subsided) creek levels. The following tasks were
performed:
1. Cross-sections including the north high bank (NHB), north toe (Ntoe), creek bottom
(CB), south toe (Stoe), and south high bank (SHB) of Fish Creek were developed from
a survey of the AVF containing approximately 10,000 data points completed during the
initial study (SubTerra, Inc., 1999). Additional survey data covering the additional area
over 17, 18, and 19-Right were subsequently incorporated into this data set.
2. An excel spreadsheet was developed that contained each of the data points for
approximately 10,000 linear feet of Fish Creek (Stations 0+00 to 100+00) with
Sections on 50-ft centers (see Table 1 and Drawing 2).
• 3. Approximately 120,000 data points, representing the ground surface over the eastern
end of Panels 16, 17, 18, and 19-Right were imported from AUTOCAD and added to
the AVF data in the spreadsheet.
4. This data set was numerically subsided in the spreadsheet. Two data sets were
created to represent the subsided surface following 17-Right extraction and the
subsided surface following 17 and 18-Right extraction.
5. Each numerically subsided data set was exported back to AUTOCAD and a new
subsided topography was created for each set.
6. The 3-D plane, representing the un-subsided water surface of Fish Creek, was then
expanded to meet the subsided ground surface and the new area of this surface was
determined. This exercise was repeated for each subsided data set representing
Panel 17-Right extraction (Drawing 3) and Panel 17 and 18-Right extraction (Drawing
4).
7. The potential effects of Panel 19-Right were evaluated using the Start Profile shown in
Figure 3 and data contained in Table 1. Subsidence in the vicinity of Fish Creek and
its AVF was estimated to be less than 6-inches and Fish Creek was not predicted to
overtop its bank at this location.
3.3 AVF Subsidence Predictions
The initial and predicted final elevations of the bottom of Fish Creek are shown in Table 2 and
• Figure 7, for 17-Right and Table 3 and Figure 8 for 17 and 18-Right, Summary data include:
• Subsidence ranging from 0 to 67 inches.
3 pN: 2002-06