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<br /> <br />Grid Method <br />' For the 2000 AHR, the AutoCAD Land Development Desktop software was used to represent <br />the two surfaces (i.e., 2000 facility topography and LTSP bottom of topsand) as triangulated <br />' irregular network (TIN) surfaces. A TIN is athree-dimensional model of a surface composed <br />of planar triangular faces. Each vertex of the TIN is a defined surface point and the points are <br />' connected optimally to make all triangular faces as nearly equilateral as possible. The Grid <br />method overlays a grid on the two TIN surfaces for which the differential volume is to be <br />calculated. For the LTSP area, a 20-foot grid was established as a series of grid cells in rows <br />' and columns. The method discards any cell that has a corner (or grid node) outside of the <br />surface boundaries. The Grid method then samples the elevations of the two surfaces at the <br />corners (or grid nodes) of each cell within the surface boundaries. The cells are then split into <br />t individual prismoidal objects and the volume calculated by summarizing the prismoidal volume <br />of all grids. <br />' Average End Area Method <br />The Softdesk/Adcadd Software Civil/Survey, with Earthworks and Digital Terrain Modeling <br />' Modules software has been used to represent the two surfaces (i.e., 1999 facility topography <br />and the 4,800-foot elevation contour) as TIN surfaces. The Average End Area method <br />calculates cross-sections from the two TIN surfaces for which the differential volume is to be <br />' calculated. For the LTSP area, previous overburden volumes were calculated using cross- <br />sections taken at 20-ft intervals. This method calculates volume by averaging adjacent cross- <br />section areas and multiplying by the distance between them. The averaging techniques used by <br />' this method results in less precise volume estimations compared to the Grid method. <br />Proposed Resolution <br />In order to address the LTSP overburden volume discrepancy, Terranext proposes to raise the <br />final reclamation grade, or the approximate original contour (AOC), by approximately 3 feet in <br />' the LTSP area. This approach appears to be consistetit with the permit Reclamation Plan <br />(Section 2.05.4 of the permit) which indicates that major disturbed areas will be returned to <br />their approximate original contour (emphasis added) and that: <br />' "if the long-term spoil pile should become inactive or both A- and B-Pits would be <br />completely reclaimed before the long-term spoil pile would be completely utilized, the <br />' remaining long-term spoil area soils will be graded and tied into the undisturbed natural <br />terrain, and then scarified, topsanded, fertilized and revegetated." <br />' Based on this approach, Terranext has revised the permit map (Appendix Q-1, Reclamation <br />Contour and Drainage Plan Map). In general. the revised map presents a 3-foot increase in <br />' the AOC for the LTSP area. The proposed AOC elevation contours were developed to <br />minimize potential impacts to the current drainage plan and maintain drainage from the LTSP <br />to the permanent west perimeter ditch and the permanent Sediment Pond 2. By increasing the <br />' AOC in this area, the remaining LTSP overburden volume was estimated to be approximately <br />' BE&K/TerraNeKt <br />