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Beck's calculations indicate that a large void (3 ft. x 3 ft. x 6 ft.) within the <br /> existing refuse would need to be located within 10 feet of the new liner to <br /> produce ponding conditions on the liner, and would need to be within 3 feet of <br /> the liner to endanger the geomembrane. Since the materials that currently exist <br /> within the landfill cannot be controlled, a buffer between the liner and potential <br /> voids must be installed. The interim final cover is a minimum of four feet thick. <br /> Additionally, the new Class III waste placement within 10 feet of the <br /> intermediate liner will be monitored to minimize the potential for voids by load <br /> checking and waste disposal inspections to verify that large, void promoting <br /> decomposable materials are not disposed within 10 feet of the intermediateiim <br /> subgrade. A four-foot thick soil zone (interim final cover) (calculated by R.W. <br /> Beck to be a sufficient buffer), the monitoring of Class Ill waste placement within <br /> 10 feet of the intermediate liner and 20 percent gradient shall serve-to-help, <br /> assure the integrity of the liner and leachate collection systems. <br /> 5.3.4.6 IMPLICATIONS TO LINER AND COVER DESIGN <br /> Based -the-settlement alaa4y�Aesc+lbed,above, the proposed overall-laodfill <br /> grades are not expected to change significantly after final closure. The <br /> anticipated differential settlements are calculated to be small and are not'17ce1y to <br /> result in significant change in the gradients of the LCRS or ponding of water on <br /> the final cover. With appropriate load checks and waste inspections, the <br /> integrity of the final cover is not likely to be impacted by the anticipated <br /> settlements of the subgrade soils and the refuse. Similarly, with appropriate load <br /> checks to eliminate large void-promoting wastes, the effects of any-voids-°at' e <br /> base of the intermediate liner system will be minimized and the integrity of the <br /> landfill containment system will be maximized. <br /> Permanent monuments will be installed in accordance with 27 CCR, Section <br /> 20950 toprovideboth horizontal and vertical control points to monitor <br /> settlement of the final site face during the post-closure period. In addition, an <br /> aerial photographic survey will be conducted of the entire landfill at final closure <br /> to produce a map with a maximum contour interval of two feet and scale of one <br /> inch equal to 100 feet in accordance with 27 CCR, Section 21142. In <br /> accordance with 27 CCR, Section 21142, an aerial photographic survey will also <br /> be produced every five years throughout the post-closure maintenance period in <br /> order to update the original topographic map produced at closure. From this <br /> information, an iso-settlement map will be produced showing the changes in <br /> Forward Landfill JTD 5-20 <br /> L:\AII ied\2000.193\Reports\fi naljtd:Sec-5.0:08/2 2/01 <br /> BRYAN A.STIRRAT S ASSOCIATES <br />