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In excavation/cut areas of each cell, scarify the subgrade in place to a depth of approximately 12 to <br />18 inches and re -compact to create a layer of compacted clay liner. Excess stripping material can be <br />used to cover the compacted clay to protect the liner from desiccation by drying or freezing. <br />3.3.4 Embankment Slope Configuration <br />With consideration for geotechnical design evaluations, maximum slopes of 3H:1V are recommended for <br />interior and exterior embankment slopes with a minimum crest width of 6 feet. <br />Case studies of embankments built with similar materials as the material observed at the passive treatment <br />system site suggest that surface slumping is possible in embankments even at shallow slope angles. The <br />surface slumps develop over time in the slopes due to degradation of the clay strength with wetting and <br />drying, and heating and cooling of the materials. Case studies show that typically the softened behavior <br />presents following 10-20 years of operation, but has been recorded as early as five years following <br />construction. <br />Ongoing monitoring of the condition of the impoundment slopes is recommended over the full life of the <br />system. In the case that surface slumps occur in the embankments, maintenance will be required to restore <br />the slopes to their original state, so as to prevent further material degradation and global stability concerns. <br />Geotechnical specification that cover the earthwork and construction of the embankments are provided in <br />Appendix D. <br />3.3.5 Bypass Ditch Configuration <br />No geotechnical design evaluations were conducted specifically for the proposed drainage ditch system that <br />bypasses the north and south side of the treatment system. The 2H:1V drainage ditch slopes are expected to <br />see some minor slumping and instabilities in these slopes given the slope materials and the steepness of the <br />slopes. However, due to their height and function it is anticipated that the regular maintenance should be <br />sufficient to maintain these slopes. <br />PEABODY_FINAL_DESIGN_TM_20ig lO10 j - s <br />COPYRIGHT 2012 BY CH2M HILL. INC . COMPANY CONFIDENT AL <br />