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SPRING 2007 Subsidence and Geologic Field Observations <br />Box Canyon, and South of Divide Mining Areas <br />Based on many subsidence measurements over longwall mining areas in the UK, it was <br />determined by investigators at NCB (1975) and by such important subsidence investigators as <br />Wardell (1971), that the amount of tilt and horizontal strain are proportional to the ratio of <br />maximum vertical displacement to overburden depth to the coal seam being mined (S,,,/d). For <br />example, under this concept, tilt and strain double where the coal extraction thickness doubles at <br />a constant overburden depth, or where the overburden thickness decreases by one-half and the <br />coal extraction thickness remains constant. <br />The subsidence prediction model used incorporates the subsidence measurements at the West <br />Elk Mine as based on the concepts developed by the NCB. The model can be further calibrated <br />and refined as more measurements are made. <br />3.1 E1 Panel Subsidence Monitoring Grid <br />The West Elk Mine has historically extracted coal mainly from the B-Seam of the Mesaverde <br />Formation. Future mining will also include the E-Seam (approximately 300 feet above the B- <br />Seam), primarily in the South of Divide mining area. As part of the ongoing data collection and <br />monitoring programs required under its permit, a new E-Seam subsidence monitoring grid was <br />proposed, developed and recently constructed. This grid is located over E-Seam longwall panel <br />1 (El) and is comprised of 119 points in one longitudinal and two transverse monument lines <br />relative to the panel orientation. This is the first panel to be mined in the E-Seam. The two <br />transverse traverses extend beyond the gate road of longwall panel E1 both to the north and <br />south. The southern end of these traverses extends to approximately the middle of longwall <br />panel E2 (at least 700 feet outside the edge of the panel). Appendix B provides the point <br />number, northing coordinate, Basting coordinate, and elevation at each of the 119 observation <br />points and conforms to previously established criteria (see Map B-1 in Appendix B). <br />This grid is planned to be resurveyed at least three months, but no more than nine months after <br />the longwall face has moved past the end of the longitudinal survey line of the E1 panel to <br />determine the amount of subsidence that has occurred and the subsidence angle of draw. Data <br />obtained from the monitoring of this subsidence grid will be used to calibrate the subsidence <br />prediction model so that a more refined analysis can be made. <br />~~ 831-032.780 <br />July 2007 <br />Wright Water Engineers, Inc. <br />Page 8 <br /> <br />