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<br />36 <br />spoil be 'placed in horizontal lifts in a controlled manner, concurrently compacted as <br />necessary to ensure mass stability.' Maximtun lift thicknesses are not specified. We <br />understand current plans aze to transport spoil by mine trucks or by pushing downhill with <br />a dozer. Lift thicknesses on the order of 4 to 6 feet are planned. if the spoil consists of <br />relatively coarse, durable particles then thicker lifts may be possible. The general <br />properties of the spoil along with actual placement and compaction procedures will need <br />to be considered to determine if thicker lifts aze reasonable." <br />The sheaz strength of spoils vary with spoil density. The overall stability of the spoil fill <br />varies with the sheaz strength of the material used to construct the fill. Spoil density <br />vazies in relation to the compaction achieved. The compaction achieved in the lower <br />portion of a spoil lift is dependent upon the material properties, the moisture content, the <br />lift thickness, and the compactive effort applied at the surface. In order to accurately <br />analyze the stability of the proposed spoil fill, the ultimate shear strength of the spoil <br />material must be determined or assumed. If assumed, the sheaz strength must be verified <br />after commencement of spoil placement. The applicant may use laboratory determinations <br />of spoil sheaz strength when completing site specific stability analyses for the spoil fills. <br />Care should be taken to determine the relationship of spoil density and shear strength, so <br />that appropriate sheaz strength parameters may be used in completing the stability <br />analysis. As an alternative or adjunct, the operator may use field compaction and loading <br />tests to verify the spoil sheaz strength properties. <br />Additional Investigations <br />Throughout Exhibit #l3, CTL/Thompson, Inc., cited material and methodology <br />assumptions which would require verification through the completion and submittal of <br />additional investigations. CTL/Thompson correctly observes on page 15 of Exhibit #13; <br />"Site specific investigation and design aze required by regulation." Exhibit #13 includes <br />a specific list of recommended additional investigations. This list is not complete. [ <br />recommend the revision of CTL/Thompson, Inc.'s list of recommended additional <br />investigations, as follows. <br />(1)Reconnaissance of tlae each fill azea to identify signs of springs, seeps, or locally <br />unstable areas, and to verify topographic conditions, <br />(2)Test borings, eF pits and oiezometers at selected locations (primarily toe azeas, sorinas, <br />semis and unstable azeasl to evaluate and samnle soil bedrock and ground water <br />conditions, <br />(3)Laboratory testing and evaluation of representative bedrock, soil and spoil engineering <br />properties, <br />(4)Durability testing to evaluate drain rock, <br />