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settlement of wastes. Considering the similarity of the final waste configurations <br /> for the currently proposed and historically proposed Forward Landfill, the CH2M <br /> Hill analyses appear applicable to the current project. Similarly, recognizing the <br /> consistency of the subsurface data collected in CH2M Hill's study and data that <br /> was collected during installation of monitoring wells at the Forward and Austin <br /> Road landfills, the CH2M Hill soil settlement analyses appear applicable to both <br /> sites. <br /> 5.3.4.2 SUBGRADE CONSOLIDATION <br /> As was the case when CH2M Hill completed its analyses in 1992, the current <br /> expansion plan for the Forward Landfill anticipates a maximum elevation of <br /> approximately 200 feet amsl. Calculat on of,the;potential consolidation-of..natiare <br /> soils under this anticipated refuse load was completed by CH2M Hill'based on <br /> the laboratory consolidation test data and standard penetrometer test blow <br /> counts collected in its geotechnical study (1992). As shown in Appendix F, these <br /> calculations indicate that the greatest refuse-induced soil consolidation will occur <br /> within currently undeveloped areas yup-to 24eet) -Assuming no significarit - <br /> settlement at the toe of the landfill, the maximum differential consolidation of <br /> subgrade soils was calculated to be two-feet in 550 feet, or about 0.36 percent. <br /> This magnitude of differential settlement can be easily accommodated by the <br /> various components of the liner system under the refuse fill. <br /> 5.3.4.3 SETTLEMENT OF NEW WASTES <br /> As shown in Appendix F, the refuse settlement analyses that were completed by <br /> R. W. Beck conservatively assumed that refuse will settle approximately 25% <br /> over a 30-year period, and that settlement during the operating life of the-iandffll <br /> can be disregarded. Since positive drainage on the finished final cover surface <br /> must be assured, the critical area for analysis was assumed to be the area of <br /> minimum (5%) grades near the center of the landfill where the depth of new <br /> refuse will be thickest. <br /> Assuming a uniform settlement of 25% of all new wastes, the analyses indicate <br /> that the 5% final cover gradient could be reduced to approximately 3.75%. <br /> Using a grid approach and assigning a random settlement value between 22% <br /> and 28%, Beck's analyses also considered differential settlement of waste <br /> materials and concluded that final grades could range from I% to 6%, but that <br /> Forward Landfill JTD 5-18 <br /> L:\Allied\2000.193\Reports\finaljtd:Sec-5.0:08/22/01 <br /> BRYAN A-STIRRAT&ASSOCIATES <br />