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<br />Memo to Susan Burgmaier <br />Southfield Coal Refuse Pile <br />page 2 <br />Geotechnical Specifics of the Report <br />In preparing it's report, TerraMatrix has retested the compaction of the coal <br />refuse pile, completed laboratory testing of specimens of fine coal refuse <br />collected from the pile, prepared an analytical stability analysis of the pile, and <br />prepared recommendations for the future compaction and compaction monitoring <br />of the Southfield Mine coal refuse pile. Compaction data submitted as a portion <br />of the quarterly inspection reports, as well as additional data collected by <br />TerraMatrix demonstrate that the coarse refuse, with a few exceptions, has <br />generally been compacted to in excess of the required 90%. The fine refuse, <br />however, has been compacted to between 53% and 86% maximum relative dry <br />density. This result is not surprising in that data demonstrates that the <br />moisture content of the fine coal refuse from the wash plant varies between <br />48% and 61 % by weight. Proctor testing performed by both Lincoln Devore and <br />TerraMatrix have determined the optimum moisture content for the fine coal <br />refuse to be in the 20% to 40' % range. <br />The presence of excess moisture within a fine earthen material will normally <br />retard short term compaction because of its consolidation restrictions. The <br />material's ability to be compressed is limited by the rate at which the moisture <br />contained within the voids can be expelled. The imposition of a compactive <br />effort will not overcome this limitation. Only a sufficient load applied over an <br />appropriately long time period will result in compression and densification of <br />the fine coal refuse. TerraMatrix's laboratory testing determined consolidations <br />of the fine coal refuse of up to 40% volumetric decrease to occur under applied <br />loads of up to 11,000 psf in 6 hours. At the Southfield Mine coal refuse pile the <br />passage of a dozer, with or without compactor or truck represents a short term <br />transient loading of effectively no consequence for compression of the fine coal <br />refuse. The long term loading is provided only by the refuse placed above the <br />layer to be compressed. Testing of the coarse and fine refuse determined a <br />normal density of between 60 psf and 95 psf for the fine and coarse refuse. <br />Therefore, this combined coal refuse will apply an average load of <br />approximately 85 psf per foot depth. As the fine coal refuse is buried it will <br />