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Figure 5b presents the net flux as a function of depth through the modeled profile for several different cover thicknesses and clearly illustrate the negative flux potential increasing (i.e., total system performance improving) as the cover section thins. 5.0 DISCUSSION 5.1 INFILTRATION As clearly shown in Figure 4, a substantial drying of final cover soils constructed at the FSL is expected. As indicated on Figure 5, this drying is expected to result in cumulative negative flux of as much as —12.60 inches per year for the 4 -foot cover section. 5.2 LANDFILL GAS EMISSIONS Title 27 CCR indicates that another purpose for final covers is to control surface emissions of landfill gas. In fact, the placement of additional, similar cover soils as a part of final closure is expected to yield superior surface emissions performance relative to the existing interim cover. Since the landfill has not exhibited excessive surface emissions under interim closure conditions, landfill gas emissions are not expected be problematic after completion of the final cover. 5.3 MAINTENANCE As noted above, the ultimate performance of the proposed 4 -foot cover section will be very sensitive to the establishment and maintenance of an effective plant community over the closure area. As a result, routine inspection and as -needed repair (and reseeding) of the cover area should be anticipated. 5.4 COST The modeling completed to date and reported herein, indicates that a non -prescriptive final cover system constructed using available on-site soils would be consistent with the performance goal addressed by the prescriptive standard and would afford equivalent or superior protection against water quality impairment. In addition, while it is estimated that closure construction costs would be the same for the prescriptive and alternative covers discussed herein (i.e., the alternative will be constructed to a prescriptive as -built standard), post -closure maintenance of the prescriptive cover to it's as -built condition would be extremely expensive (likely requiring reconstruction every few years) and almost certainly ineffective since desiccation can occur in a matter of weeks or months. 6.0 RECOMMENDATIONS The results obtained from the LEACHM analysis (Figure 5) indicate that four feet of final cover material constructed and maintained as discussed herein will perform effectively at the site and this cover section is therefore recommended. -11- C:\2005.0082\FOR WARD/ForwxrJCOVER.DOC\7/13/2005 Geologic Associates