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Postmining Topography . <br />General. Backfilling end grading of the spoil material will produce a postmining topography similar to the <br />original land form. The design of the postmining land form utilizes existing data. The purpose of the <br />design is to construct a postmining land form which is adequate for defining drainage patterns and for <br />review and analysis by regulatory authorities. <br />The design requires adjusting the original land form elevations for the removed coal seam and the swell of <br />the overburden. Data necessary to develop the new elevations and calculate volumes ere overburden and <br />coal thickness, bottom of the mined seam, original ground surface elevations, and the limits of the area <br />to be mined. All of these data are available in a computerized drill hole data base and from topographic <br />maps. <br />Volume Calculations (Premining Topographyl. All of the volumetric calculations used in the development <br />of the postmine topography are shown on Tables 20-1 and 20-1 A. Please refer to Figure 20-1 for a <br />sketch of the volume locations. The following methods were used in determining those volumes. <br />Premining Material Volume. A computer model developed by Peabody called STAMP was used to • <br />determine the premining material volume. All pertinent drill hole data is input into the modal: location, <br />depth, seam thickness, overburden thickness and stratigraphy, quality, hole elevation, etc. With this <br />information, the computer can determine volumes of material by pit, mining block, year, or the entire <br />mining area. The volume determined, in this case, contains all the material, from the ground surface to <br />the coal seam bottom within the boundary of the area to be mined. <br />Virgin Overburden Material Volume. STAMP is again used to determine the volume of material between <br />the original ground surface and the top of the coal seam to be mined. <br />Total In-Place Coal Volume. This is the difference between the premining material volume and the virgin <br />overburden material. <br />Recoverable Coal Volume. It is estimated that the actual recovery rate at Seneca II-W will be <br />approximately 1,650 Tons per acre toot ITPAFI or 93.6 percent of theoretical density 11,762 TPAF1. The <br />recoverable coal volume is determined by multiplying the in-place coal volume by the actual recovery rate. <br />• <br />4 Revised 9/98 <br />