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• areas, known as Cameo Refuse Disposal Areas No. 2 and 3. The <br />proposed slope and bench configurations were supplied to Rocky <br />Mountain Geotechnical by Powderhorn Coal Company for the slope <br />stability investigation, The plans submitted to Rocky Mountain <br />Geotechnical indicated that an underdrain system was to be <br />utilized for the refuse piles, along with a permanent diversion <br />ditch along the upper part of the coal piles. <br />1.3 SUMMARY <br />The slope stability study indicated that the proposed mine coal <br />waste refuse disposal piles will have factors of safety exceeding <br />the required 1.5 as required by the CMLRD even with a high <br />phreatic surface. This factor of safety assumed that no <br />• underdrains would be constructed. It is our recommendation that <br />underdrains are not necessary for the coal refuse piles. The <br />proposed refuse piles will have an average slope of approximately <br />2.5 horizontal to 1 vertical. The only possible location of <br />potentially unstable slope conditions that could occur would be <br />at the toe of the refuse piles. We feel that this slope <br />instability is unlikely but can be easily monitored by the <br />placement of monitoring piezometers along the toe of the refuse <br />piles. If high groundwater conditions unexpectedly occur, then a <br />toe drain could be constructed along the face of the coal refuse <br />piles to lower the phreatic surface. <br />More specific information of analyses performed and results can <br />be found in the body of this report. <br />2 <br />