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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2010-0016 -16- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS NORTH COUNTY LANDFILL SAN JOAQUIN COUNTY <br /> <br /> were considered using the Morgenstern-Price method. Critical interface failure envelopes were developed for the modules based on the results of laboratory shear testing (up to maximum expected loads) and other factors. Computed static factors of safety ranged from 1.5 (Module 1) to 2.0 (Module 3), while computed yield accelerations ranged from 0.055g (Module 4) to 0.11g (Modules 1 and 3), indicating that all critical slopes would be stable under static conditions. Dynamic slope stability analysis was also conducted based on both probabilistic and deterministic approaches that yielded the following sets of conditions: <br />a. Probabilistic Approach <br />1) Spectral Period < 0.4 Seconds - MPE = 6.4 at 54 km, PGA = 0.098g (Central Valley Coast Range Fault System). <br />2) Spectral Period > 0.4 Seconds - MPE = 8.0 at 126 km, PGA = 0.085g (San Andreas Fault System) <br />b. Deterministic Approach <br />1) Small earthquake – MPE < 6.5, PGA = 0.115 <br />Calculated dynamic factors of safety ranged from 1.04 (interim slope) to 1.43 (Modules 4 through 11). Since all dynamic factors of safety were below the 1.5 minimum specified under Title 27, Section 21750(f)(5)(D), a more rigorous analysis of the data (i.e., deformation analysis) was performed using the Makdisi-Seed method (1977). The maximum calculated displacement by this method was 0.17 inches (interim slope), well within the maximum specified under Title 27 for seismic slope stability (6 inches). <br />CLOSURE AND POSTCLOSURE MAINTENANCE <br />61. As described in the PCP/PCMP (Appendix B, JTD), landfill closure activities will include grading and cover installation; improvements to precipitation and drainage controls; additional/modified leachate and LFG control facilities; installation of LFG and groundwater monitoring systems; removal of structures and other closure-related activities. <br />a. After reaching final refuse elevations, the landfill will be contiguously graded as a single unit. Landfill grades will be generally the same as those for the individual modules described in Finding 52 (e.g., 5% minimum slopes on top deck, 3H:1V maximum exterior slopes, benching). <br />b. Landfill precipitation and drainage controls will also be generally the same as those for the individual modules described in Findings 52 through 53 (e.g., top deck grading and berms, bench drains, O/S drains etc.), except as follows: <br />1) There will be no ISB. Runoff from the eastern fill area will be discharged via the perimeter drain to the wetlands mitigation area and South Paddy Creek in the northern part of the site.