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GeoSyntec Consultants <br />3.3 Estimated Closure Date <br />Title 27, CCR §21790(b)(7) an estimate of the closure date based on volumetric <br />calculations, including supporting documentation. The estimate shall account for <br />the effects of settlement and for volume occupied by daily cover material; <br />Three general mechanisms typically contribute to the settlement of solid waste <br />[Edil, et al., 1990]. These are: 1) waste compression; 2) migration of fines and soil <br />cover into waste voids; and 3) waste decomposition. Since Forward compacts waste <br />immediately following placement, waste compression and fines migration will likely be <br />completed soon after final refuse placement. Significant settlement resulting from <br />waste decomposition typically occurs at municipal solid waste landfills during waste <br />placement and continues for several years following landfill closure [Sharma and <br />Lewis, 1994]. Approximately half of the waste settlement in the WMU B area is <br />expected to occur within 5 years after final waste disposal Waste settlement <br />calculations can be found in Appendix B. <br />Based on volume calculations from the proposed top of foundation layer grading <br />plan (see Figure 3-1), the remaining airspace in the WMU B disposal area is <br />approximately 670,000 cubic yards as of 1 June 1999. Assuming a Class III waste to <br />daily cover soil ratio of 6 to 1, the remaining Class III waste capacity in the WMU B <br />disposal area is approximately 574,000 cubic yards. <br />Based on current Class III filling rates of 25,000 to 30,000 tons/month, at an <br />assumed in-place, compacted unit weight of 1,755 pounds per cubic yard (pcy), the <br />WMU B area will take approximately 549 days to fill. With an assumed filling start <br />date of 1 June 1999, and waste disposal occurring 312 days a year, the WMU B area <br />should reach capacity by the Spring of 2001. <br />A minimum 2 -ft thick intermediate soil cover will be placed on the side slopes in <br />conjunction with waste placement. The intermediate cover will be placed on the top <br />deck of WMU B within 30 -days after reaching capacity. A 1 to 2 -inch thick hay/straw <br />layer will be placed over the intermediate soil cover to minimize rainfall induced <br />erosion. A temporary drainage control system will be constructed as well. <br />2 Remaining airspace represents the total available volume minus the 2 -ft thick foundation layer. <br />J:\ALLIED\FORWARD\CLOSUREPLAN\REPORT 3-2 99.11.30 <br />C� <br />