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-8- <br />• with the exception of a near-surface, weathered, Tan sandstone material <br />which had a slake durability index of about 85 percent. Franklin and Chandra <br />(International Journal of Rock Mechanics, 1972) present a classification <br />system for sedimentary rock under which the materials tested with stake- <br />durability index greater than 90% would be described as "Rock" with very <br />high to extremely high durability and is consistent with OSM/TM-2/83. <br />The washwater obtained after the second cycle of the slake durability <br />test was tested for pH to judge the acid-forming characteristics of the <br />proposed drain materials. All measured pH's were in the range of 7.5 to 8.0, <br />indicating non-acid forming rock. <br />Permeability <br />In a loose state, we believe the spoil materials exhibit extremely high <br />permeability. The material is a broken angular rock consisting of sandstone <br />with some shales. After compaction, the materials decrease somewhat in <br />permeability. Method of placement and compaction have significant <br />influences on permeability. For the purpose of estimating the possibilities for <br />spoil saturation, we estimated overall permeability of the fill to range <br />between 1,000 and 10,000 feet per year, with 10,000 feet per year (or higher) <br />a more likely figure. '.Ne believe the placement of the fill in comparatively <br />thick lifts will result in higher permeabilities at the base of each lift. <br /> <br />