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• existing spoil stockpile at Nucla Mine, the overburden/interburden will likely be <br /> stratified by individual distinct lifts of different lithologic material. Lithologic Unit <br /> 1 material will typically be placed near the base of the stockpile with a thin topdressing <br /> of Units 2, 3, and 4. As the stockpiled material is returned to the final pit, mixed <br /> Units 2, 3, and 4 will be placed near the pit base and subsequently covered with Unit 1 <br /> material. Mixed Units 2, 3, and 4 have mean pH and ABP values of 6.0 and -1.8, <br /> respectively, which are both considered suitable for aquifer or root growth medium <br /> material (Tab 6, Attachment 6-1, Table 6-1-3). <br /> The following overburden/interburden handling techniques will be utilized after the lower <br /> Dakota Coal has been removed from the box cut pit. Initially, the upper unconsolidated <br /> overburden will be removed by dozer or scraper and placed into the adjacent pit void. <br /> Cast blasting will be utilized to fracture the remaining consolidated <br /> overburden/interburden. During cast blasting, portions of Units 2, 3, and 4, in addition <br /> to the lower part of Unit 1, will likely be projected into the adjacent pit. Lastly, <br /> dozers and scrapers will be utilized to remove the remaining overburden/interburden <br /> material down to the top of the Lower Dakota Coal. <br /> Where blending or normal burial are ineffective (as defined by the Regraded Spoil <br /> Monitoring Program), Unit 1 overburden will be selectively handled to replace a four-foot <br /> root growth medium at the regraded spoil surface. In these situations, unsuitable spoil <br /> will be topdressed with a minimum of four feet of suitable material (includes replaced <br /> topsoil thickness). <br /> Lastly, ameliorating reclamation practices will primarily be utilized in those areas where <br /> unsuitable spoil reaction, acid-base potential, particle size, saturation percentage, <br /> salinity, or sodicity values are identified by the regraded spoil quality control program. <br /> Reclamation practices will include either a selectively handled suitable spoil topdressing <br /> or incorporating adequate quantities of agricultural grade limestone. <br /> Regraded Spoil Monitoring Program. In order to provide a feedback system to check the <br /> reliability of the overburden sampling and analysis program, a regraded spoil sampling <br /> program will be initiated. The upper four feet of regraded spoil will be sampled prior to <br /> topsoil replacement with a hydraulic soil sampler, a bucket auger, or other suitable <br /> equipment to ensure that a suitable root growth medium is provided. Two representative <br /> 21-5 Revised 08/19/88 <br />