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We believe the existing refuse is comparatively stable. The results of our analyses <br />indicated a factor of safety of 1.9 for the existing configuration, and the measured <br />strength, moisture conditions and density of the till. Parametric studies indicated <br />variations in refuse properties did not lower the computed factor of safety below 1.5. <br />2. Our analyses indicated the presence of 20 to 25 feet of very wet materials near the <br />existing refuse surface does not decrease the stability of the future refuse configuration <br />below a computed factor of safety of 1.5 provided future materials are placed in a drier <br />condftion. We believe these materials may remain in place provided actions are taken <br />as described in ftem 3. <br />3. We recommend Wyoming Fuel Company take measures to reduce the moisture present <br />within the refuse materials at the time of placement. We understand additional process <br />is being added to reclaim portions of the wet "coal" fines from the refuse. These <br />changes should be monitored to determine what effects they will have upon the refuse <br />materials which are placed at the RDA. <br />4. Our laboratory studies and stability calculations indicated the compacted density of the <br />refuse materials is not a significant determinant of the performance of the RDA from a <br />stability perspective. We believe it is possible to continue to place and compact the <br />materials using lift thicknesses and compaction procedures consistent with the previous <br />placement methods provided future refuse is not placed with excessive moisture. <br />5. If the process cannot be changed to significantly decrease the moisture of the refuse <br />materials, then other remediation measures will likely be required. These measures <br />would likely include provision of vertical and/or horizontal drainage systems within the <br />constructed fill. In our opinion, process control is more desirable than these types of <br />precautions. <br />LIMITATIONS <br />The analyses and conclusions presented in this report were developed based upon the <br />conditions described in the report. Variations in subsoil conditions between our borings are always <br />possible. We estimated the existing conditions based on our exploratory borings, field and laboratory <br />investigations and our experience. If conditions change, or are found to differ from our assumptions <br />we should be contacted to review our analyses, conclusions and recommendations. <br />This investigation was conducted in a manner consistent with that level of care and skill <br />ordinarily exercised by members of the geotechnical engineering profession currently practicing under <br />similar conditions. No other warranty, express or implied, is made. It has been our pleasure to serve <br />10 <br />