2008-10-07_PERMIT FILE - C1981047 (4)

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• The 1993 repair will be accomplished by installing clean rock intercept drains at the top and bottom of the slide areas and at any obvious water source. The clean rock intercept drains will be installed as shown on new Exhibit DD. The slump area in the central portion of the bench will be repaired by grading the material back up the slope. To the extent possible, the waste material and cover material will be separated. The material will be placed and compacted in generally horizontal lifts. The clean rock intercept drains will be constructed as the fill is placed. The area of the 1988 failure where there are scarps and a bulge will also be repaired. The cover material will be excavated to expose the waste material to identify the location of any water sources. The cover material will then be replaced and compacted in generally horizontal lifts. Clean rock intercept drains will be constructed as the fill is placed. Construction of the clean rock intercept drains is considered the best way to relieve the source of water in the waste material. If the source of water is given a path of relief, then it will not saturate adjacent material and cause pressure to form that could generate another failure. As long as the source of water in the waste material is intercepted and relieved, the long term stability • of the bench should be assured. ADDITIONAL MONITORING Monitoring points P-5, P-6 and P-2 may have been destroyed by the slide. During the bench repair, an effort will be made to preserve and repair these monitoring points. The clean rock intercept drains will probably not flow, except possibly in the spring, and then not every spring. The outlet points of the intercept drains will be monitored if they exhibit consistent flow patterns. The stability monitoring has been valuable to show that, overall the bench is stable. The piezometer monitoring has shown the waste material does have water in it and that the water in the cover material and waste material are not related. Additional piezometer monitoring may be desirable, however the information generated by additional monitoring would probably not be of any significant value. SCHEDULE The best time to perform the bench repair work is during September. • Delaying the work until late in the year will allow the slump area to dry as much as possible. The delay will also allow the seeding 113viii (Rev. 08-11-93)