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~ ~~ 4 <br /> <br /> The material should be spread in uniform layers of not <br /> more than 24 inches in loose thickness and then compacted to <br />' at least 90 percent of the maximum dry density as determined <br /> by the AASHTO* T99-74 or equivalent test method ("Standard <br /> Proctor"). This may be achievable by selectively routing re- <br /> fuse haulage equipment over the pile. <br /> <br /> It is possible that unusually fine-grained materials may <br />' be produced during initial mine construction and development. <br /> These should not be incorporated into the toe of the pile <br /> because of their potential low strength. <br />' The surface of the waste pile should always be maintained <br />l <br />f <br />h <br /> at a s <br />ope o <br />more t <br />an 5 percent to prevent ponding of water <br /> on the surface and the potential of seeping of the surface run- <br />' off into the pile. During winter months, snow should be period- <br /> ically removed from the temporary pile surface prior to place- <br />s ment of the waste material. <br /> i <br />' 4.6 NON-TOXIC COVER <br /> Subsequent to grading and prior to revegetation, the <br />' waste pile should be covered with non-toxic, non-combustible <br /> and impermeable soil. The impermeability condition is required <br />t to prevent surface water seepage into the pile. <br />t The clayey soils which are present to a considerable <br /> depth over the bench area should be suitable for this pur- <br />' pose. Permeability tests by Chen ~ Associates (1980) showed <br /> permeability values between 6.5 x 10-~ and 3.5 x 10-q cm/sec; <br /> soils of this type will comprise excellent material for an <br /> impermeable cover. The soil cover should be placed in lifts <br />' *American Association of State Highway and Transportation <br /> Official <br /> iNC <br /> . <br />c,EO+noaoca+w~mw. <br />