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conveyed to a flare at the south end of the site where it is destroyed (Figure 6). According to the County, the flare inflow averages approximately 164 cubic feet per minute. Effectiveness of the LFG system is indicated by the absence of landfill gas at the perimeter monitoring wells and prevention of further VOC impacts indicated by a reduction of the number of individual constituent VOC detections. This system is presently extracting as much LFG as possible, as indicated by the low methane concentration of the gas reaching the LFG flare station. In December 2008, five new LFG extraction wells were installed, two more than originally proposed. The additional wells were located to control LFG impact to groundwater near wel MW-5. The vacuum at these wells was set at-0.1 inches of water. 3.0 MITIGATION ALTERNATIVES As stated above, impacts to groundwater have been identified in the shallow aquifer only. Impacts appear to occur primarily in the Corcoran Clay, but do not extend to the deeper, regional aquifer. Accordingly, this EFS is focused on addressing groundwater impacts in the rshallow aquifer. 3.1 POTENTIAL REMEDIAL ALTERNATIVES Remedial approaches to VOC-impacted groundwater include source control, active responses, and semi-passive to passive systems. Source control involves minimizing the available contaminant sources within the waste prism by minimizing leachate or landfill gas formation or by extracting leachate or landfill gas. Examples of active responses include ex- situ pump and treat alternatives and in-situ air sparging, vapor extraction, and bio- inoculation. Semi-passive measures include "funnel and gate" treatment technologies, "permeable walls," and bio-enhancement. An example of a passive response would be reliance on intrinsic (natural) biodegradation of VOCs in groundwater. Some or all of the potential treatment systems may be appropriate to mitigate the release at the site. 3.2 DESIGN BASIS FOR SOURCE CONTROL ALTERNATIVES Source controls are those engineering measures designed to reduce the amount or production of waste decomposition products before groundwater is impacted. These controls may be active or passive. Examples of active source controls include a landfill gas extraction system or a leachate extraction system. These controls physically remove vapors Engineering Feasibility Study Geo-Lo Page ■ 8 Corral Hollow Sanitary Landfill ASSOCIATESS January 25,2013