2008-04-22_PERMIT FILE - C1981017 (4)

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~~ • .-- design of the pile, we. do not consider these local variances as `~ critical for the stability. _ The inspection showed, however, that end-dumping or pushing of the material over the crest of the pile may have a very negative inf 1 uence on the stabi 1 i ty of the waste pi 1 e's outer slopes. Shallow sloughs, slides and mudflows can develop when the ~. material is saturated. This was apparently the case during the last month; the material from the upper part of the pile was pushed across the crest. Because of the high moisture content, local stability problems were encountered. We recommend to modify the construction procedures and to proceed with the construction of final slopes of the pile. We recommend that the existing slopes of the pile are classified • either as temporary or as final. We do not see any need to try to achieve compaction at temporary slopes. On the other hand, we feel that the permanent slopes should be built with due care. They should be built at the design slope of 2(H) : 1(V) and compacted as specified. End-dumping or pushing the material across the crest should be avoided. We recommend to flatten the final slopes to 2(H) 1(V). This flattening can be achieved by pushing the material from the -~ vicinity of the pile crest down to the design toe of the pile. With his method, the material of surficial sloughs and slides will be removed and pushed down the slope. We recommend that a thickness of at least 15 feet, measured perpendicular to the surface of the pile, is removed down toward the toe of the pile. The foundation of the toe area of the pile should be prepared as specified in the design and as required by M LRD regulations. The material should be spread in lifts not exceeding 12 inches of loose thickness, and it should be compacted by at - least three passes of a crawler tractor. A final slope of 2(H) ' 1(V) should be strictly maintained. We recommend to eliminate the intermediate benches if they are not required for other purposes. • The construction should be supervised by Mid-Continent per- sonnel in the same manner as recommended for the coal refuse dis- posal facility. Periodical compaction control, using the nuclear i density devices, should be performed. If piezometers are required for the future control of ground f water conditions, we recommend to install piezometers only in the outer shell of the pile, close to the final crest. We feel that '~' the piezometers should be installed only after the construction • of the waste pile ,is terminated. r~ _. • ~ _. ~ 2 1 ` ._ . susn ..r~iH _ _ ._._... _ _ ~_.~_ ~ c~.w~