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gradient is maintained in the drainage ditches to facilitate <br /> the removal of water. A maximum gradient of 50/1. is recommended <br /> by OSM for the top of the fill . In conjunction with this value, <br /> we recom-mend a minimum gradient of 2%, in order to provide posi- <br /> tive drainage and prevent water from standing or ponding on the <br /> fill. A minimum gradient of 2% is also recommended for the <br /> terraces or benches . <br /> It is our understanding that an <br /> 8% average gradient is desired forthe top of the fill in the <br /> east-west direction. Since a maximum aradient of 5% is allowed <br /> for the top of the fill to minimize erosion, it will be necessary <br /> to contruct the top of the fill as a series of broad, low ter- <br /> races, with steeper slopes in between. The terraces should have <br /> a slope between "l/' and 5%, and the slopes between terraces <br /> should not e,:coed 50`/o (2 : 1 slope) . This should provide an <br /> adequate solution, providing it meets the approval of OSM or <br /> other regulatory agencies . <br /> All topsoil, vegetation, or other <br /> objectionable materials must be removed from the fill area prior <br /> to fill placement. After clearing is completed, the ground <br /> surface should be scarified to a depth of 6 inches, until the <br /> surface is free from ruts and uneven features. Where fill is to <br /> be placed against slopes steeper than 20%, the native slope <br /> should be stepped or benched prior to fill placement. The sur- <br /> face of these benches should be scarified as described above. <br /> The scarified surface should then be brought to the proper moisture <br /> -9- <br />