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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 %%ill <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 will <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 />i <br />