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<br />Preliminary Closure and Postclosure Maintenance Plan 2-4 Department of Public Works/Solid Waste <br />North County Recycling Center and Sanitary Landfill County of San Joaquin <br /> <br />2.4 Decommissioning of Environmental Control Systems <br />Internal soil gas wells SG-5, -6, and -7 will be decommissioned prior to the extension of the liner <br />into that area and overfilling with refuse, and will not be part of closure activity or closure costs. <br />Decommissioning will be as approved by the applicable regulatory agencies. At this time, it is <br />anticipated that the boreholes will be re-drilled and the resulting hole filled with concrete slurry <br />or other approved fluid. Single-probe soil gas well SG-4 will be retained for VOC sampling, if <br />required. <br />All other environmental control systems will remain operable during closure and in the <br />postclosure period. These include: groundwater monitoring, leachate collection, landfill gas <br />migration monitoring, landfill gas collection and control, and vadose zone monitoring and <br />surface water monitoring. The landfill gas (LFG) control system will be expanded to include the <br />new lined areas as they are constructed. <br />2.5 Description of Closure Activities <br />Sections 21790 (b)(8)(A) through (F) require Preliminary Closure Plans to provide a preliminary <br />description and schedule for the elements discussed in the following subsections. <br />2.5.1 Final Cover <br />The County proposes placement of an evapotranspirative (ET) cover as an engineered <br />alternative to the prescriptive 1-foot-thick low-permeability soil layer, as allowed under Section <br />21090(a). This proposal is based on: <br />• The success of the ET cover at the Foothill Sanitary Landfill and other landfills <br />• Suitability of soils at the NCRC&SL for an ET cover (sandy silts) <br />• Recent determination by Regional Water Board staff that a barrier layer comprised of <br />GCL requires seven feet of overburden soil to compress the GCL sufficiently to provide <br />the equivalent of one foot of 10-6 cm/sec permeability. <br />The County will obtain approval of the ET closure method prior to construction. <br />2.5.2 Final Grading and Drainage Plan <br />The Final Grading and Drainage Plan incorporates the following constraints and objectives <br />(Figure 3 and Drawing): <br />1. Maximum fill elevation to 320 feet msl. <br />2. The minimum 100-foot setback of waste from the west, south, and east property <br />boundaries. The setback includes the perimeter soil berm and outboard drainage <br />ditch (Drawing 2 and Drawing 3 - Detail 1).