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TECHNICAL MEMORANDUM Page 15 E t June 3, 1992 SAC31583.AC.ZZ generally overconsolidated, which suggests that most of the anticipated foundation settlement will occur during placement of the refuse fill. We anticipate that up to approximately 1 foot of the total settlement will occur as the refuse fill is being placed,.with the remainder of the anticipated settlement occurring after refuse fill placement is complete. Based on available subsurface information, abrupt differential foundation settlement is not anticipated. For purpose of base grading and preliminary design of the Ieachate collection system for the proposed -landfill extension, foundation settlement may be assumed to be negligible at the toe of the landfill. Assuming no significant tlenaent at the..toe :of _the landfill and an ultimate settlement of 2 feet under the maximum refuse fill height, the estimated maximum differential foundation settlement is 2 ,fz-et in 55,0 feet, <�r approximately 0.36 percent. Refuse Settlement The general mechanisms that will typically contribute to refuse settlement of a landfill AMIL include waste compression, migration of finer`waste particles and soit-covevinto the-voidSLLof the waste, and waste decomposition. Waste fill compression and fines migration typically occur rapidly and are accelerated by providing adequate waste compaction. It is our understanding that the waste material for the proposed landfill extension -Will be compacted immediately following placement, and waste compression and fines migration N"ill therefore likely be completed soon after final refuse placement. Significant settlegnems due to the waste decomposition typically occur at municipal solid waste landfills. The proposed landfill extension will, however, accept mainly commercial and industrial waste -and settlement from waste decomposition is therefore not expected to be significant. Based on the above discussions,. it is anticipated that the majority of the refuse settlement at the Forward landfill will be attributed to waste fill compression.=and fines migra .on ..and N611 occur during the active life of the landfill. Assuming that approximately 10 percent of the maximum landfill thickness will settle due to waste compression and fine migration, -the maximum settlement from this mechanism is about 20 feet. Some postclosure settlement may occur due to waste decomposition, however this settlement is anticipated to be small and will be monitored during postclosure by performing aerial surveys and generating isosettlement maps.