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