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-= i -2- difficult than placement of fill in the lower, steeper potions of the hillside in the disposal area. ..Starting fill construction as currently proposed, will allow development of compaction procedures in the flatter `ground. After the equipment operators have been trained in the flatter area it should be less difficult to obtain the desired compaction in the lower, steeper areas. The toe of the proposed initial fill is near the transition from the upper relatively flat areas into steeper, sloping side slopes. 'In our opinion. a buttress fill at the base of this initial area of fill is desirable to minimize any risk of instability during the construction period when men and equipment will be working below this fill. bur analysis of stability of the initial fill indicates that the fill would be stable with an adequate factor of safety without the buttress fill, however, considering that this will be the initial construction with a large number of variables involved, we believe additional safety of the buttress fill is desirable. The toe buttress should consist of a trench excavated into the hard, gray-blue portions of the underlying rock formations a minimum of 3 feet. The trench should be excavated with side slopes approxi- mately 1:1 with the bottom of trench width approximately 30 feet. Backfill for the initial buttress fill should consist of the blue-gray sandstones and siltstones developed from the initial box cut. Overburden stripping from the initial box cut other than that required to be saved as topsoil can be placed in areas above the initial buttress. After satisfactory materials are exposed in the box cut, placement and compaction of the but- tress fill can start. We plan to have a representative on-site during the period to observe the bottom of the key cut, approve materials for fill and work with your crews in developing a satisfactory compaction procedure. The rock for under drains should be available before any of the drainages are crossed. The actual construction sequence and details will have to be coordinated with you in the field. If we can clarify our opinions or be of further service in this matter, please call. Very truly yours, CTL/THOMPSON, INC. By ompson, r. RWT:dm 7078 (3 copies sent)