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Corral Hollow LFG System Audit and Upgrade Report ' During our October field investigation, these newly installed wells were operating under vacuum conditions. Results of testing at perimeter migration monitoring wells (GW-1 through GW-9, all t probes), including those in the northern site perimeter near VOC-affected groundwater monitoring wells MW-5 and MW-8, showed no evidence of methane or elevated levels of carbon dioxide in soils outside the fill. Based on these findings we conclude that the recent measures implemented by The County have shown to be effective for LFG control at the Site. Effectiveness of Existing System ' The following summary takes into consideration SCS's review of GCCS performance and monitoring data provided by the County, and the findings from the Operations Review. In ' general, the Operations Review showed that with minor exceptions, the existing gas collection system components (i.e., extraction wells, collection system piping, condensate management system)appear to be in generally good operating condition with no apparent issues. Continued Vacuum and Flow Rate Adjustments. Theoretically, efficient LFG control is maintained by extracting the gas at a rate that is at or slightly greater than the rate being ' generated within the landfill. If the extraction rate is less that the generation rate, the excess uncollected gas may become a source for compliance issues (i.e., subsurface migration, VOCs in soils, odors, surface emissions, etc.). If the extraction rate is greater than the generation rate, ' then this may result in air intrusion into the individual well casings or the waste mass, or operational problems with combustion equipment. At landfill sites, the LFG generation rate generally peaks one year after waste deliveries cease, , and slowly declines with time. Based on operating data in early 2013 and the latest round of monitoring (October 2013), several individual extraction wells are being operated in an overpull condition, in which gas is be extracted at a rate faster than it is being generated. This finding is ' based upon the fact that methane levels at each extraction well are much less than 50% by volume. This is also supported by SCS's October 2013 site visit findings that methane quality to flare is approximately 20% by volume. We recognize that lower overall gas quality is the ' unavoidable result of County efforts to control impact to groundwater by extracting as much gas from the system as possible, particularly in the north and northeast portion of the site where impact to groundwater is indicated. LFG extraction wells in this area (EW-40 through -51) ' generally show lower methane content which is to be expected given the operational objective for those wells and their location at the periphery of refuse fill. Based on operating data for 2011 through 2013, the overall gas capture rate for the Site has ' averaged approximately 26 scfm methane. However, during our field investigation the collection rate of methane was 20 scfm (or 1.2 million BTU/hr), slightly above the minimum rated heat ' capacity of the flare (1 million BTU/hr). Operating under these conditions can be challenging; however, during 2012,the GCCS "up-time"was 96.4%(San Joaquin County, 2013). In the interim it appears that some operational vacuum and flow rate adjustments can be made to optimize gas capture and overall GCCS performance. This can be accomplished by continued "fine-tuning" adjustments according to the County adjustment protocol - throttling individual ' 10 December 201 3