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• Phasing of the investigation • Construction Schedule • Financial Assurances Many of these topics contained a series of questions of concern, this Revised EFS is arranged to respond to the emails topic format. During routine groundwater monitoring, VOCs have in the past been detected in MW -3. In addition, VOCs also have been detected in single -probe soil gas monitoring wells SG -1 through SG -11. It is believed that LFG from the unlined Module "I" has migrated to the groundwater table and may be driven by the over -liner constructed over a portion of Module "I" in 2006. Although it appears that low levels of VOCs have been present in the groundwater at MW -3, the detection of VOCs in well MW -3 has not been consistent between monitoring events. For example, the most recent third quarter 2014 monitoring results obtained from MW -3 do not report any VOCs present as shown in Appendix A. Existing Gas Collection and Control System (GCCS) The existing landfill GCCS system consists of a series of headers and laterals with nine (9) vertical LFG extraction wells in Module "I". The current extraction wells are installed approximately 600 -ft apart within the centroid of the waste mass of Module "I". Wells are installed between 43 and 103 ft. below ground surface (bgs) and constructed of 4 -inch PVC casing with screen lengths varying from 21 to 50 ft. LFG from Module "I" is routed via network of various -sized collector pipe to the onsite LFG-to-Energy power plant where it is combusted in internal combustion engines and used to make electricity. Any excess LFG, or during plant shutdowns, an enclosed flare is used to combust recovered LFG. Proposed Enhancement Design The following section describes the landfill GCCS enhancements to the LFG extraction system that will be installed in Module "I" as shown in Appendix B, Figure 1. CVRWQCB Question: There must be a justification for the number of proposed wells. Why only seven wells? What data does the County have to support the number of proposed wells? County Response: The existing GCCS at the FSL, which consists of nine (9) extraction wells, has demonstrated general ability to control surface emissions and methane migration from the landfill in accordance with applicable regulations namely USEPA 40 CFR Part 60, Subpart WWW; CCR Title 27 Division 2, Chapter 3 Article 6, CCR Title 17, Sections 95464 through 95467, and the San Joaquin Air Pollution Control District Permit No. N-4070-0-2 and N-4070-1-6. Foothill Sanitary Landfill 5 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014