2018-01-03_PERMIT FILE - C1994082 (12)

Home Browse Search

Volume Calculations (Postmining Topography). A computer program was used to determine the initial postmine topography. The program allows the engineer to manipulate the postmine surface. The material can be picked up, swelled, and moved to an adjacent pit. The program then generates a postmine topography map based on the new elevations. The postmine stream channels and highwall reduction areas must be incorporated into this preliminary topography map. These contours are then digitized in x, y, z coordinates and stored in a computer file for contour generation. This preliminary map is then used to develop a final map. A computer program is used to generate the volume between the top of the postmining surface and the bottom of the coal seam. The limiting polygons used to determine material volumes were the areas bounded by the coal recovery lines. This volumetric measurement should approximate the total pit spoil volume as shown on Table 20-1, Postmining Landform Mass Balance. In determining the amount of spoil that will end up inside the coal recovery limits, a distinction must be made between the material such as where it originated and where it ended up, as in highwall reduction or graded areas outside the coal recovery limits. External overburden material as noted on Table 20-1 is highwall reduction material pushed into the pit area. External spoil material is material that, in the grading process, ended up outside the recovery line and actually increased the elevation (fill) of the area surrounding the pit areas (recovery areas). This is a relatively minor amount of the internal spoil material volume. The source of this material is generally attributed to blending the postmining topography into adjacent hills or slopes. It usually takes several tries before the volume measured on the topography map even approximates the target volume. The contours must be adjusted on the computer screen and the volume rerun until the postmining volume is within five percent of this number. To get the calculated volume to compare exactly with the volume measured from the postmine topography map would be beyond the accuracy of any mapping exercise. Contour maps are generally only accurate to within half the contour interval. Pre- and Postmine S1 The objective of any postmine topography design is to establish a landform that approximates the premine conditions. The design of a surface that duplicates premine conditions is not within the scope of the final output. After the postmine topography contours were generated, another check was made to see how the postmine contours compared to the premine contours. There were 15 cross-sections drawn across the property. Locations of the cross-sections were chosen to give a reasonable representation of the pre- and postmining conditions. Cross-section locations are shown on Exhibit 20-2, Postmining Topography, and the pre- and postmining cross-sections are presented on Exhibit 20-2A, Premining 7 Revised 02/99