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Postmining Topography <br /> Since mining operations have been performed with scrapers and dozers at Nucla and will be <br /> performed with scrapers and dozers at Nucla East instead of draglines, the postmining <br /> topography was estimated based upon a 15 percent swell factor. The proposed revised <br /> postmining topography at Nucla was generated based on actual (existing) contours. it was <br /> assumed that all swelling of the material has been accomplished. Further handling of the <br /> material could cause additional swelling, but compaction caused by reclamation equipment <br /> would offset any difference in volume. <br /> The postmining topography map was created by generating cross sections through the mined <br /> area, balancing the available non-coal material and generating a contour map to provide a <br /> landform surface compatible with the postmining land use, pre-existing drainage patterns <br /> and to provide a stable landform surface. <br /> After the initial postmining contour map was developed, the existing and proposed surfaces <br /> were volumetrically compared with the aid of a computer program called SURFER. The <br /> postmining contour map was adjusted until the difference between the cut and fill volume <br /> was less than one percent. Typical cross sections through the mining areas are shown on <br /> Exhibits 20-4 (Nucla-10 sheets) and 20-11 (Nucla East-5 sheets). These cross sections <br /> show existing, original, and postmining ground. The areas mined and coal seams remaining <br /> are also shown on the Nucla Mine cross sections. <br /> Cross sections A-A' through E-El (Exhibit 20-4) at Nucla reflect the proposed postmining <br /> Land surface for Mining Area No. 1. The grading in this area will allow for irrigation in <br /> the future, although Peabody does not propose to irrigate or construct the irrigation <br /> laterals. Please refer to Appendix C, Tab 20 for discussion of the reclaimed drainage <br /> channel, and Exhibit 20-5 for the drainage profile K-K'. Appendix C also shows the SEDCAD <br /> output for this channel. <br /> Mining disturbance in Mining Area No. 2 was restricted to the vicinity of cross section <br /> F-F'. The premining line depicts the ground as it was prior to the redisturbance in that <br /> area. The postmining line depicts the ground as it currently exists (reclaimed). The <br /> remaining cross sections G-G' through J-J' show the ground as it currently exists. <br /> Additional mining was not conducted in Area No. 3 as originally proposed. No further <br /> grading is proposed for Mining Areas 2 or 3. <br /> 20-5 Revised 05/24/91 <br />