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Ms. Natalia Subbotnikova Page 3 <br /> November 9, 2023 <br /> returned to the site to re-measure landfill gas concentrations in gas migration probe VW-4, after an <br /> apparent anomalous methane concentration was recorded on October 25, 2023. All results <br /> discussed here-after include the corrected gas concentrations recorded at VW-4 on November 9, <br /> 2023. Gas concentrations were measured using a GEM 2000 hand-held portable gas monitor. <br /> The results are presented in Table 1 and field sheets are included in Attachment A. <br /> RESULTS <br /> At the gas migration monitoring probes (VW-1 through VW-10), methane was only detected at VW-4 <br /> and VW-5D (0.01%). Methane was not detected at either of the vapor extraction wells (EW-1 and <br /> EW-2). At the passive vent pipes(VP-1 through VP-4), methane was detected at concentrations <br /> ranging from 0% (VP-2) to 17.3% (VP-4). <br /> Oxygen concentrations at all sample locations ranged from 0.0% to 19.3%. Carbon dioxide <br /> concentrations at all sample locations ranged from 0.1%to 35.3%. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Before installation of the passive soil vapor extraction trench, methane concentrations historically <br /> exceeded 5% at the following probes: VW-4, VW-5S, VW-5D, VW-6S, and VW-6D. Since the <br /> passive soil vapor extraction trench was installed in September 2006, methane concentrations <br /> decreased at these probes to less than 5% during the following quarter and have continued to be <br /> less than 5% during the subsequent monitoring events. <br /> Methane concentrations measured at all gas migration monitoring probes during 4Q23 were less <br /> than 5%, Methane concentrations measured at the vapor extraction wells were both less than 5%. <br /> Methane concentrations at the passive vent pipes ranged from 0.0% to 17.3%. <br /> If you have any questions regarding this report, please contact Scott Little at(916)207-3053. <br />