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0 <br />Underground Mining <br />A significant area containing spoil fills could be planned for future underground <br />mining. We understand the mining will be designed to minimize subsidence below fill <br />areas. ff sign cant subsidence is possible, then additional analysis will be required to <br />evaluate potential effects on the fills and develop mitigation alternatives. <br />ADDITIONAL INVESTIGATIONS <br />This analysis, and previous investigations, have documented soil conditions and <br />engineering properties. The excess spoil fill and sedimentation pond embankment <br />stability analyses are considered applicable to future fills and ponds. Only Fills 15 and <br />19 have a steeper valley slope than used in our typical section (Fig. C-1). <br />We believe investigations at future fills can use the stability analysis and soil <br />properties documented in this report. Site specific reconnaissance will be required to <br />• confirm conditions. <br />As drain rock sources are identified, durability should be confirmed with <br />laboratory testing. <br />The scope of investigation and design should evolve as investigations are <br />completed. Confirmation of reduced scope investigations by the CDMG will need to be <br />negotiated. The use of the stability analysis from this investigation along with compiled <br />engineering properties from site specific investigations should allow for more efficient <br />investigation/design procedures. <br />• LORENCITO COAL COMPANY, LLC <br />LORENCITO SURFACE MINE -PHASE I <br />CTLR 32, 611 113 <br />