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1.0 INTRODUCTION <br />Estimated subsidence magnitudes presented in this Draft Environmental Impact <br />Statement for the Red Cliff Mine, Project Area containing the Coal Lease Application and <br />the Existing Coal Lease areas are planned for principally longwall mining of coal north of <br />Mack and Loma Colorado and the south facing Book Cliffs and east of Colorado State <br />Highway 139 as indicated on the general location map titled Red Cliff Mine, Proposed <br />Mine Facilities and Rail Spur. The Coal Lease Application area is east of the Existing <br />Coal Lease that includes the active McClane Canyon Mine and the closed and reclaimed <br />Munger Mine. <br />2.0 DEFINITION OF TERMS AND SYMBOLS <br />Terms used to evaluate and analyze subsidence processes and amounts are described <br />below. <br />Longwall Mining: See Affected Environment/Subsidence for an overview of underground <br />coal mining. <br />Mining Panel: A rectangular mining area where mine openings are developed and coal is <br />extracted. In longwall mining panels, development entries, or gate roads, are driven at <br />either side of the panel boundaries and the intervening coal is extracted with a longwall <br />cutting machine. <br />Headgate: Entries and crosscuts driven on the side of the mining panel adjacent to <br />unmined coal, and on the side of the panel that is in the direction of further panel <br />development and used for removal by belt of coal as cut from the longwall face and <br />bringing ventilation to the longwall face. <br />Tailgate: Entries and crosscuts driven on the opposite side of the mining panel from the <br />head gate entries and provide a path for return ventilation air from the face. <br />Panel Length and Width (W, L): The length and width of the longwall panel where coal is <br />being extracted. <br />Subsidence: The vertical downward movement of the overburden and ground surface <br />caused by extracting the coal. <br />Maximum Subsidence: The maximum vertical downward movement of the overburden <br />and ground surface above the center of the panel caused by extracting the coal. <br />Tilt and Maximum Tilt (M): The inclination of the ground surface caused by mining the <br />coal in a longwall panel, the vertical displacement difference between two points on the <br />ground surface divided by the horizontal distance between these points; maximum tilt is <br />the maximum inclination that develops as the ground surface deflects downward towards <br />the center of a panel, i.e. the subsidence trough. <br />Maximum Strain (+E, -E): Strain is the change in length between two points of <br />measurement divided by the original distance between these two points (unit change in <br />length); tensile strain (+e) is the unit elongation between any two points on the surface <br />moving further apart (unit elongation) as the ground surface deflects downward towards <br />C-1 <br />DBMS 293 <br />