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Memorandum to Ryan Sweetwood and Kathy Welt <br />August 2, 2010 (Revised February 1, 2011) <br />Page 2 <br />(Horizontal Distance <br />Angle of Draw (¢) =Tan-1 ` Vertical Distance )' <br />where: <br />the horizontal distance is from the nearest point on the ground surface with no discernable <br />longwall subsidence perpendicular to a vertical line projected from the boundary of the <br />longwall panel, and <br />the vertical distance is from the top of the coal seam at the longwall panel boundary to the <br />ground elevation equal to the point of no discernable longwall subsidence. <br />Table 1 provides a summary of the calculated angle of draw at the various panel edges using ground <br />elevation data from the E-seam survey monuments and top of E-Seam elevations from Map 17 of <br />MCC's permit document. This information has been revised from that originally submitted (based <br />on interpretation of E-Seam overburden mapping) in WWE's August 2, 2010 memorandum. This <br />revision is in response to a question raised by Mr. Tom Kaldenbach of the Colorado Division of <br />Reclamation, Mining and Safety regarding the calculation of the angle of draw. He'd questioned <br />whether the point of no discernable longwall subsidence was located on the ground surface or on a <br />normalized horizontal line representing the differential vertical displacement, as is usually depicted <br />in reference materials, including that of the National Coal Board. After further review of the <br />relevant literature and WWE's previous work, we concur that the line determining the angle of draw <br />is the representative angle between a vertical line over the panel extraction boundary and a line <br />drawn from the edge of the panel to the point on the ground representing no discernable longwall <br />subsidence. <br />TABLE 1 <br />Angle of Draw Calculations <br />Monument Used Horizontal Distance* <br />(feet) Vertical Distance <br />(feet) Angle of Draw <br />NO <br />10 330 1139 16.6° <br />37 340 1290 14.8° <br />57 290 1197 13.6° <br />80 290 1165 14.0° <br />101 380 1145 18.4° <br />*All horizontal distances are perpendicular to the coal extraction boundary.