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the pile could be constructed to a maximum height of 75 feet while <br />• maintaining a factor of safety greater than 1.5. This report, presented <br />in Exhibit 18, Geotechnical Investigations, serves as the design basis for <br />ongoing and future refuse pile construction at the Southfield Mine. <br />In 1989, EFCI determined that additional refuse capacity would be required <br />based upon future mine production projections. Accordingly, EFCI <br />submitted a technical revision. TR-07, Coal Refuse Pile Expansion, to <br />expand the coal refuse facility. EFCI utilized the design criteria <br />specified in the RMG report for construction of the expanded pile area. <br />Appropriate modifications were made to designs for the <br />diversion/collection system and final stockpile configuration. The <br />modified final stockpile configuration is illustrated by the Coal Refuse <br />Pile Expansion Map, (Map TRO7-1), included in Exhibit 15, Minor and <br />Technical Revisions. <br />Initial refuse stockpile designs and associated stability analyses assumed <br />mixing of coarse and fine refuse prior to placement and compaction. From <br />• a practical operating standpoint, effective mixing prior to placement is <br />difficult and appears to have little beneficial effect on material <br />compaction and stability. Over a period of years, successive <br />modifications of placement practices reflecting site operating experience <br />resulting in a "layered fill" placement technique. Typically, a lift of <br />fine refuse is placed and compacted, followed by one or more lifts of <br />coarse refuse. <br />The MLRD expressed concerns relative to any potential impact of layered <br />placement and variable percentages of coarse and fine refuse on refuse <br />pile stability. In order to address these concerns EFCI completed, <br />submitted, and obtained MLRD approval of a technical revision, TR-14, <br />Reevaluation of Coal Refuse Pile Stability, in early 1992. This stability <br />evaluation concluded that layered placement and variable coarse/fine <br />percentages would have no adverse impact on stability and that original <br />design parameters were overly conservative resulting in understatement of <br />the factor of safety. <br /> <br />C:IW O0.K~PR!\8fiPB6PfRIf.RE V <br />a~.~ ~m 4.10.2R Revised April 1993 <br />