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