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.; .~ <br />Mountain Coal Company <br />West Elk Mine <br />Semi-annual Subsidence Report <br />The most current subsidence survey for the West Elk Mine was performed in October <br />1993. The survey was completed by Messenger and Associates. The survey was <br />conducted using radial and level loop survey methods. The instruments used were a Wild, <br />T-1, theodolite; a Nikon , ND 20, distance meter; and an unspecified level. <br />The following tables reflect the northings, eastings, average pre-mining elevations, the <br />previous report elevations (July 1993), the current survey elevations, subsidence since the <br />October 1992 report and total subsidence. Additionally, though not required for the semi- <br />annual subsidence monitoring report, subsidence profiles are being submitted with this <br />report that show the subsidence normalized (the original surface topography elevations are <br />set at zero) for comaparison. <br />The following tables indicate that the maximum total subsidence to-date is 8.42 feet and <br />occurs over both the F and B Seams at point No. 41. Point No. 41 occurs over the center <br />of the ] st Northwest Longwall Panel. The subsidence to-date is well within the range of <br />the predicted subsidence, (Exhibit 60). In this area of two-seam mining, complete <br />maximum subsidence can be calculated by simple addition of the maximum predicted <br />subsidence for both the F and B Seams. Included for reference is Table 3.3.4.2 from <br />Exhibit 60. The table shows the total predicted subsidence for the 2-seam mining is 10.22 <br />feet. <br />The visual effects of subsidence were limited to surficial cracks over the F- Seam No. 1 <br />West, No. 1 South, Room and Pillar Panel and over the first, second, and third B-Seam <br />Longwall panels. The cracks were northwest southeast trending and were located directly <br />over, or centered over, the panels. The cracks were various widths, from approximately <br />two inches to 16 inches. The lengths ofthe cracks were discontinuous, but did not exceed <br />100 yards in any length of run. Displacement at or near the cracks was not perceptible. <br />The cracks seen last year over the B-Seam, 1st Northwest Longwall Panel, have healed <br />well and many are not visually perceptible. <br />Mining advance was limited to the B Seam development in the B-West Mains, and the <br />Third and Fourth Northwest Headgates, during 1993. The Longwall retreated in the B 1, <br />B2, and B3, Northwest Longwall Panels (N1VLW) in 1993. The first two panels were <br />completed and the Longwall was set-up and retreat begun in the B3 NWLW Panel in <br />October of 1993. The attached map, Subsidence Monitoring Network, shows the <br />relationship of mining advance during 1993 and 1994, with the subsidence network. <br />Development mining passed beneath the G-26B spring in the 4th Northwest Headgate, at <br />cross-cut 28, in November 1993. No additional mine inflows were encountered and no <br />)(changle ~s/77to spring flow due Ito mining are anticipated. <br />l"~ ~`'V IG~ )lip / VJ {/:~~ I ~rc~ j. VJ I~cl nn <br />/GbJ ~ ~00- /Od p jr~ <br />