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• Oakridge further proposes to place the in-pit reject in the pit as shown on Figure 5-4. <br />Reference is made to the stability report compiled by Kenneth C. Ko. Mr. Ko found <br />that an overall slope of 3:1 (approximately 18°) had a safety factor of 1.8. The <br />material is also applicable to the backfill in the pit because it is comprised of the same <br />material (sand, silt and clay shale). <br />The subject report stated: <br />"The most critical areas of the fill slope from a slope stability standpoint, will <br />be in areas where the foundation soils may become saturated in time." <br />It should be noted that the reject will be comprised primarily of shales, sandstones and <br />coal fines that, when combined, will have very similar strength characteristics to the <br />other fill materials. The subject materials will not be saturated and will lose moisture <br />with time and rehandling. Any retained moisture from crushing and pit separation will <br />allow the reject to compact better, thus increasing the friction angle and cohesion. <br />It is not feasible to simulate these minute changes relative to placement of such <br />materials in the backfilled pit. However, as shown on Figure 36 in Appendix 5-6, a <br />safety factor of 2.4 is calculated for near surface slope considerations. A 1.5 factor of <br />• safety was calculated when near surface grades approach 1-112:1 and up to 2:1. <br />Further, the general safety factor fora 3:1 slope will be 1.8. Thus, it is reasonable to <br />assume that because the reject will compact better than other fill, its influence in the <br />factor of safety will be no better than other fill, its influence in the factor of safety will <br />be no less than that created by the unconsolidated fill. Personal communication with <br />Mr. Robert W. Thompson of CTL-Thompson, Inc., confirms the above. <br />The introduction of the reject into the configuration set forth above should not diminish <br />the factor of safety created by the baclcfdl without intermingled reject. It is projected <br />that the reclaimed pit with intermingled reject will have a factor of safety that is no less <br />than 1.5. <br />The sulfur content of the coals and their associated over and underlying strata, range <br />between one and three percent. Abandoned coal mine records for the Durango, <br />Colorado area document no problems with acid mine waters and burned spoil piles. <br />Both of these facts indicate that the coal processing wastes, which will be generated by <br />the Carbon Junction Mine, have a limited potential to beacid-forming and have no <br />reasonable probability of being combustible when placed in the overburden. <br />Seriling Pond, <br />No coal settling ponds are planned for the subject operations. <br />Technical Revision OS (v 1.3) 5-15 <br />Revised 9/1997 <br />