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TECHNICAL MEMORANDUM <br /> Page 15 <br /> June 3, 1992 <br /> SAC31583.AC.ZZ <br /> generally overconsolidated, which suggests that most of the anticipated foundation settlement <br /> will occur during placement of the refuse fill. We anticipate that up to approximately 1 foot <br /> of the total settlement will occur as the refuse fill is being placed,.with the remainder of the <br /> anticipated settlement occurring after refuse fill placement is complete. <br /> Based on available subsurface information, abrupt differential foundation settlement is not <br /> anticipated. For purpose of base grading and preliminary design of the leachate collection <br /> system for the proposed-landfill extension, foundation settlement may be assumed to be <br /> negligible at the toe of the landfill. Assuming no significant settlement at the toe of the ' <br /> landfill and an ultimate settlement of 2 feet under the maximum refuse fill height, the <br /> estimated maximum differential foundation settlement is 2 feet in 550 feet, or approximately <br /> 0.36 percent. <br /> Refuse Settlement <br /> The general mechanisms that will typically contribute to refuse settlement of a landfill <br /> include waste compression, migration of finer waste particles and soil cover into the voids of <br /> the waste., and waste decomposition. Waste fill compression and fines migration typically <br /> occur rapidly and are accelerated by providing adequate waste compaction. <br /> It-is our understanding that the waste material for the proposed landfill extension will be <br /> compacted immediately following placement, and waste compression and fines migration -,kill <br /> therefore likely be completed soon after final refuse placement. Significant settlements due <br /> to'the waste decomposition typically occur at municipal solid waste landfills. The proposed <br /> landfill extension will, however, accept mainly commercial and industrial waste and <br /> settlement from waste decomposition is therefore not expected to be significant. <br /> Based on the above discussions,.it is anticipated that the majority of the refuse settlement at <br /> the Forward landfill will be attributed to waste fill compression and fines migration and 'Ail] <br /> occur during the active life of the landfill. Assuming that approximately 10 percent of the <br /> maximum landfill thickness will settle due to waste compression and fine migration, the <br /> maximum settlement from this mechanism is about 20 feet. Some postclosure settlement <br /> may occur due to waste decomposition, however this settlement is anticipated to be small <br /> and will be monitored during postclosure by performing aerial surveys and generating <br /> isosettlement maps. <br /> r - <br />