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r ' Corral Hollow LFG System Audit and Upgrade Report • Vacuum was measured at all 51 extraction wells, generally at levels below 0.5 inches r water column. This confirms that as of the test dates and during the interval monitored, the system was operating in accordance with one of the primary requirements of the CDO: maintaining negative pressure at each extraction point. Vacuum ranged from 2.75 inches of water column (EW-30) to 0.01 inches in (EW-12, - 16, -46 and -50). Wells with lower applied vacuum were those with low methane content, consistent with the County's adjustment protocol (San Joaquin County, 2013). • Methane was not detected in any landfill gas perimeter migration monitoring well (GW-1 through GW-9), during the October 2013 inspection, and the Site was in compliance with ' 27 CCR requirements affecting public health and safety. SCS's monitoring results are consistent with data from recent monitoring events by the County. • Elevated levels of carbon monoxide gas were not detected in the main header line serving the current GCCS for any in fill refuse extraction well. Therefore, SCS concludes that there is currently no indication of subsurface combustion within the refuse. rIn summary, we saw no evidence that the existing GCCS components are compromised, or that major repairs or modifications are warranted to maintain existing gas extraction capabilities. ' There are limited opportunities to improve optimize gas capture and quality and flare performance via operational changes, as discussed in the engineering evaluation section below. ' Engineering Audit/Evaluation and Conclusions SCS performed an engineering review of the effectiveness of the existing LFG system and newly r installed LFG extraction wells. We also evaluated alternatives to enhance landfill gas source control. Specifically, SCS considered the following: ' • Continued vacuum and flow rate adjustments to GCCS extraction points, and/or overall control system adjustments. ' • Repairs or upgrades to GCCS system piping to improve vacuum/flow capabilities. • Repairs or upgrades to gas condensate collection and handling systems to improve vacuum/flow distribution. ' • Installation of additional in-fill or vadose zone extraction wells. rEffectiveness of Newly Installed Extraction Wells Per the CDO, this audit included the evaluation of the recently installed corrective measures for the Site that included removal of refuse found to the north of the historic closure cover and placement of excavated refuse under a newly constructed cover section. During the closure project of 2013, the County also installed seven additional gas extraction wells to control groundwater impact. 1 9 December 2013 1