PERMFILE61656

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 04e-3 Northern Mining District Subsidence Evaluation
• Media Type: D
• Archive: No

SubTerra, Inc. Twentymile Coal Company 05/31/00
Northern Mining District Subsidence Evaluation -Final Report
• 1. Introduction
Over the next five years, Twentymile Coal Company (TCC) will expand its operations into the
Northern Mining District (NMD) ofthe Foidel Creek mine near Steamboat, Colorado. Current plans
call for mining to be completed in five (5), 1,000•ft wide longwall panels (Panels 12 through 16)
during this period. The layout of the mine workings and surface features is shown on Drawing 1.
There are two principal structures and natural features that will be affected by subsidence in the
NMD, the Energy Spur track, and Fish Creek. A short section of Foidel Creek will also be
undermined by the first longwall panel, Panel 12 Right. This report covers the prediction of
subsidence associated with extraction of each ofthe longwall panels; an evaluation ofthe impacts
to the Energy Spur; an evaluation ofthe impacts on Fish Creek and its Alluvial Valley Floor (AVF);
and an evaluation of subsidence effects on Foidel Creek.
2. Subsidence Prediction
Twentymile Coal Company (TCC) has developed an extensive subsidence database from
monitoring longwall panel extraction in the West, Southwest, and Eastern mining districts. This
data has been submitted to the Division of Mines and Geology in semi-annual subsidence
reports and in reports attached to permit documents.
TCC has supplemented these published data with results from monitoring the county road,
power lines, and the Energy Spur track which crosses both the Eastern and Northern mining
districts during mining Panels 9, 8, and 7-Right in the Eastern mining district.
The process of incorporating these data in the current predictions is described in the following
• paragraphs:
1. Figure 1 was compiled from records of maximum subsidence from the Western,
Southwestern, and Eastern mining districts and shows the relationship between
maximum subsidence and the width/depth ratio for the Foidel Creek mine. This
figure was used to predict maximum subsidence values for the 1000-ft wide panels at
depths of 800, 1,100 and 1,400 feet, which represents the range in conditions for the
study area.
2. Time phased data from the initial surveys of Panels 1, 2, and 3 in the Western Mining
District (Subsidence Line 12000E), representing the surface response to the first,
second, and third panel extraction, were used to predict the effects of 12-Right, and
subsequent panel, extraction. These data are contained in the semi-annual reports
and in prior permit submittals.
The above data from the Western Mining District has shown that the first longwall
panel only produces 90%ofthe full maximum subsidence that is realized by
subsequent panels. This phenomena is built into the predictions and illustrated in
Figures 2, 2A, and 3.
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 1 LLW and 2LLW) and data gathered during mining Panels 9, 8, and 7-Right
in the eastern mining district. These data are contained in the semi-annual reports
and prior permit submittals.
•
PN: 98-12