2013-09-27_REPORT - C1980007 (4)

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Memorandum to Ryan Sweetwood and Kathy Welt August 2, 2010 (Revised February 1, 2011) Page 2 Angle of Draw (0) =Tan -1 ( Vertical Horizontal Distance ), Distance where: the horizontal distance is from the nearest point on the ground surface with no discernable longwall subsidence perpendicular to a vertical line projected from the boundary of the longwall panel, and the vertical distance is from the top of the coal seam at the longwall panel boundary to the ground elevation equal to the point of no discernable longwall subsidence. Table 1 provides a summary of the calculated angle of draw at the various panel edges using ground elevation data from the E -seam survey monuments and top of E -Seam elevations from Map 17 of MCC's permit document. This information has been revised from that originally submitted (based on interpretation of E -Seam overburden mapping) in WWE's August 2, 2010 memorandum. This revision is in response to a question raised by Mr. Tom Kaldenbach of the Colorado Division of Reclamation, Mining and Safety regarding the calculation of the angle of draw. He'd questioned whether the point of no discernable longwall subsidence was located on the ground surface or on a normalized horizontal line representing the differential vertical displacement, as is usually depicted in reference materials, including that of the National Coal Board. After further review of the relevant literature and W WE's previous work, we concur that the line determining the angle of draw is the representative angle between a vertical line over the panel extraction boundary and a line drawn from the edge of the panel to the point on the ground representing no discernable longwall subsidence. TABLE 1 Angle of Draw Calculations Monument Used Horizontal Distance* (feet) Vertical Distance (feet) Angle of Draw ( (P) 10 330 1139 16.60 37 340 1290 14.80 57 290 1197 13.60 80 290 1165 14.00 101 380 1145 18.40 `All horizontal distances are perpendicular to the coal extraction boundary.