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Total Pit Spoil Volume. The premining overburden volume is then multiplied buy the swell factor (1.153) to <br />determine the total pit spoil volume:. The 15.3 percent swell was used in determining postmine topography <br />at the Seneca II Mine. Geologic materials are similar at Seneca II-W and, therefore, the 15.3 percent <br />swell was used for the Wedge seam. However, for the PR-03 (Sage Creek/Wolf Creek seams) mining <br />area (II-W South Area), SCC has determined that a swell factor of 1.17 is more applicable and, therefore, <br />this swell factor has been used for the South Area. <br />This volume is compared to the premining material volume and logically concludes that the postmine <br />surface elevation will generally bc~ lower in elevation than the premining condition. With this in mind, <br />calculations and mapping can proceed for generation of a realistic postmine topography map. <br />Volume Calculations /Postminina Tooooraohv). A computer model developed by Peabody was used to <br />determine the initial postmine topography. The program called PDS, or Postmining Design System, allows <br />the engineer to manipulate the postmine surface. The material can be picked up, swelled, and moved to <br />an adjacent pit. The program than generates a postmine topography map based on the new elevations. <br />This preliminary map is then used to develop a final map. The postmine stream channels and highwall <br />reduction areas must be incorporated into this preliminary topography map. These contours are then <br />digitized in x, y, z coordinates and :;toyed in a computer the for contour generation. <br />A computer program called DCA (DCA Engineering Software, 1989) is used to generate the volume <br />between the top of the postmining surface and the bottom of the coal seam. The limiting polygons used to <br />determine material volumes were: the areas bounded by the coal recovery lines. This volumetric <br />measurement should approximate the total pit spoil volume as shown on Tables 20-1 and 20-1A. In <br />determining the amount of spoil that will end up inside the coal recovery limits, a distinction must be made <br />between the material. Where it originated and where it ended up, as in highwall reduction or graded areas <br />outside the coal recovery limits. External overburden material as noted on Table 20-1 is highwall reduction <br />material pushed into the pit area. External spoil material is material that, in the grading process, ended up <br />outside the recovery line and actually increased the elevation (fill) of the area surrounding the pit areas <br />(recovery areas). This is a relatively minor amount (0.7 percent) of the internal spoil material volume. The <br />source of this material is generally attributed to blending the postmining topography into adjacent hills or <br />slopes. It usually takes several tries before the volume measured on the topography map even <br />approximates the target volume. l-he contours must be adjusted on the computer screen and the volume <br />rerun until the postmining volume is within five percent of this number. To get the calculated volume to <br />compare exactly with the volume measured from the postmine topography map would be beyond the <br />~J <br />PR-05 10 Revised 01!06 <br />