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• <br /> 1 <br /> ■ Average monthly leachate and average plus one standard deviation monthly <br /> leachate shown as a graph over a one year period. Recommended use is to size <br /> leachate pretreatment facilities. <br /> For this report an analysis was conducted for each of the 6 phases of the landfill expansion. Two <br /> scenarios of landfill operations were examined, one with no surface water run-off management, <br /> and one with an aggressive surface water run-off management program. A summary of estimated <br /> leachate generation in the "no management" case is shown in Figure 5A and shows that <br /> excessively large volumes of leachate may be expected. Figure 5B shows that annual leachate <br /> volume may be reduced significantly by adopting an aggressive approach to stormwater <br /> management. This approach would require the construction of berms,dikes, and other diversion <br /> structures to divert run-off from landfill areas that have undergone Intermediate closure to the <br /> stormwater system rather than the leachate system. Figures 6 through 11 show detailed leachate <br /> generation estimates by phases, under the assumption of aggressive stormwater management. <br /> The landfill design and phasing is currently in the preliminary stage and the above cases may not <br /> reflect the final design. This model can be used to quickly evaluate phasing alternatives design <br /> and the effects of stormwater separation from the leachate system. <br /> 6. Drainage Layer Design Criteria <br /> The HELP model was used to evaluate the design criteria for leachate lateral spacing and <br /> drainage layer permeability. The federal solid waste disposal facility criteria 40 CFR 258, <br /> commonly referred to as Subtitle D, requires the leachate collection system be constructed to <br /> maintain less than a 30-cm (11.8 inch) depth of leachate over the liner (40 CFR 258.40(b)). <br /> Except for the Initial condition where there is exposed liner without waste in-place yet, all of the <br /> landfill conditions examined showed a maximum head on the liner of less than one inch; <br /> therefore, the separation of leachate collectors and drainage layer as indicated on the drawings <br /> meets or exceeds the regulatory requirements. <br /> s� <br /> w <br /> 1 <br />