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<br />Review of 2000 and 2001 Topog~aahic Surfaces <br />Since the reliability of the topographic map work is essential to most <br />activities relative to reclamation, it is important to build reliability into this <br />database. As with previous years, a review of the contour discrepancies <br />(year to year) has been conducted. A review of the 2000 and 2001 <br />topographic surfaces indicates several discrepancies in areas that were not <br />disturbed during 2001 (i.e. areas where no work was conducted). These <br />discrepancies appear to be related to the use of different reported survey <br />control points between the 2000 and 2001 topographic maps. In order to <br />perform accurate volumetric estimates for remaining B-Pit airspace, <br />remaining spoil, and stockpile topsand, 2001 topographic contours were <br />modified to be consistent with 2000 topographic contours in areas that were <br />not disturbed during 2001 site activities. <br />Computer-Aided Drafting Svstem Software Explanation <br />• For the 2001 AHR Report, volumes were computed using the Grid method <br />provided in the AutoCAD Land Development Desktop software. This <br />method creates triangulated irregular network (TIN) surfaces to represent <br />topographic and reclamation surfaces (i.e. AOC). A TIN is a three- <br />dimensional model of a surface composed of planar triangular faces. Each <br />vertex of the TIN is a defined surface point and the points are connected <br />optimally to make all triangular faces as nearly equilateral as possible. The <br />Grid method overlays a grid on the two TIN surfaces for which the <br />differential volume is to be calculated. For volumetric calculations, a 20- <br />foot grid was established as a series fo grid cells in rows and columns. The <br />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 <br />two surfaces at the corners (or grid nodes) of each cell within the surface <br />boundaries. The cells are then split into individual prismoidal objects and <br />the volume calculated by summarizing the prismoidal volume of all grids. <br />• <br />AHR-2001 -127- <br />