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I~'~ <br /> <br />Underground Mining <br />A significant area containing spoil fills is planned for future underground <br />mining (Fig. 1). We understand the mining will be designed to minimize subsidence <br />below fill areas. If significant subsidence is possible, then additional analysis will be <br />required to evaluate potential effects on the fills and develop mitigation alternatives. <br />ADDt170NAL INVESTIGATIONS <br />Site specific investigation and design are required by regulation. We believe <br />the scope of these investigations should include: <br />1. Reconnaissance of the fill area to identify signs of springs, seeps, or <br />locally unstable areas, <br />2. Test borings or pits at selected locations (primarily toe areas) to <br />evaluate soil/bedrock and ground water conditions, <br /> <br />3. Laboratory testing and evaluation of representative soil and spoil <br />engineering properties, <br />4. Durability testing to evaluate drain rock, <br />5. Confirmation of the suitability of the stability analysis presented in this <br />report or re-analysis, <br />6. Evaluation and monitoring of constructed fill to confirm design <br />assumptions. Monitoring could consist of ground water well(s) near <br />the toe. <br />After specific investigations for several fills in various conditions are <br />completed, we believe it should be possible to extrapolate spoil and soil engineering <br />properties using classification testing. Reconnaissance and/or subsurface <br />investigation at each disposal area, by a qualified engineer familiar with site <br />conditions and the assumptions used in the stability analysis will be required. <br />Alternatives to modify the type of subsurface investigation required should <br />• also be possible. For instance, where site conditions and previous investigations <br />LORENOITO COAL COMPANY <br />CM 25,151 <br />15 <br />