2011-02-02_REPORT - C1980007

• Permit No: C1980007
• IBM Index Class Name: REPORT
• Doc Date: 2/2/2011
• Doc Name: 2010 Spring Subsidence Report Operators Response Memo
• From: Kathy Welt
• To: DRMS
• Permit Index Doc Type: Subsidence Report
• Email Name: TAK
• Media Type: D
• Archive: No

WWE
MEMORANDUM
To: Ryan Sweetwood and Kathy Welt
Mountain Coal Company, LLC
Via Email
From: Wright Water Engineers, Inc.
Gary D. Witt, P.G., and Richard Dunrud, P.E.
Date: August 2, 2010 (Revised February 1, 2011)
Re: E-Seam Angle of Draw
During the latter half of 2009, Mountain Coal Company, LLC's (MCC) mining of the first E-seam
panel (Panel E-1) in the South of Divide mining area extended westward beyond the subsidence
monument grid established at the eastern end of this panel (Map B-1 of Appendix B in the Spring
2010 Subsidence and Geologic Field Observations report [Spring 2010 Report]). Survey data
collected prior to, during, and following mining beneath the area has been collected in a timely
manner as required by the permit. This data was included as Appendix B in the Spring 2010 Report
prepared by Wright Water Engineers, Inc. (WWE) in October 2010.
Subsidence monument grid data is useful in evaluation of many subsidence parameters including
displacement, tilt, strain, angle of draw, break angle, and angle of major influence. Of these, the
primary focus is generally given to the angle of draw because of the geometric considerations which
stem from this particular parameter (i.e., panel layout relative to features such as water resources
and geologic hazards). This memorandum lays out the specific calculations for angle of draw as
developed from data obtained as part of the subsidence monitoring program.
Figure 1 shows the location of the 124 subsidence monitoring grid monuments relative to longwall
panel E-1. Of particular interest in the subsidence grid survey data is the identification of the
subsidence trough boundary along each traverse. Monument locations with no discernable longwall
subsidence (approximate edge of subsidence trough) are listed .in Table 1.
The angle of draw (Cp) is defined as the angle between the projection of a straight line from the coal
extraction boundary (i.e., edge of longwall panel) to the outer limit of the observed elevation change
caused by the longwall extraction and the vertical reference relative to this coal extraction boundary.
(see Figures A and B of Appendix A of the Spring 2010 Report). The calculation is relatively
simple, once the elevation change caused by the coal extraction panel is differentiated from the
influences of the surrounding chain pillars. Therefore, the trigonometric equation is as follows:
Wright Water Engineers, Inc., 2490W. 2e Avenue, Ste. 100A, Denver, C080211
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