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9.0 SURFACE AND SUBSURFACE DRAINAGE The permanent drainage facilities within the landfill will have the capacity to carry peak flow from a 100 -year recurrence storm. Storm runoff volumes were calcu- lated and drainage facilities were sized using applicable design criteria from Manual for Storm Drain Design, San Joaquin County, California. Surface runoff within the landfill and contributory run-on from the adjacent areas east of the landfill will be carried in perimeter ditches and discharged to the natu- ral drainage swales along the south and west perimeters (see Figure 9-1). Per- manent perimeter berms will be constructed along the limits of the active module areas to divert surface water from the active fill area. Initial lifts in each module will be placed during dry weather months to prevent accumulation of runoff in the active fill module. I All lifts within the module will be sloped at a minimum of 2 percent toward the perimeter to promote drainage. Ad- vancement of the working face will be reversed, after the initial lift, to progress from the perimeter to the interior access road. Runoff within the module will be diverted from exposed refuse by constructing a berm in advance of the working face. The berm will be skewed to direct flow toward the adjacent module to be collected in a temporary storm drainage sump. Collected runoff will be pumped from the sump to the perimeter drainage ditch. A perimeter berm will be constructed around the landfill to prevent run-on from adjacent areas from entering active disposal areas. The berm, when complete, will direct run-on around the landfill to existing drainage swales downgradient of the landfill. During landfill development, the berm will be constructed in phases either one module ahead of the active fill module or to one of the existing drainage swales. If the phased construction of the berm interferes with any major natural drainage channels passing through the landfill area, the berm will be completed so that drainage can flow around the landfill area without being im- peded. The discharge of sediment -laden runoff will be controlled by silt fences during the excavation, preparation, and operation phases. The silt fences will be construc- PJ9 9390219A.00W 41 Rev. 0 July 19, 1989