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16 January 2025 <br />Project No. 24-7860 <br />Page 3 of 4 <br />and carbon dioxide), at the gas migration monitoring probes (VW-1 through VW-10), <br />vapor extraction wells (EW-1 and EW-2), and the passive vent pipes (VP-1 through VP- <br />4). Concentrations were measured using a GEM 5000 hand-held portable gas monitor. <br /> <br />The results are presented in the Field Measurements Table included in Attachment A. <br /> <br /> <br />RESULTS <br /> <br />At the gas migration monitoring probes (VW-1 through VW-10), methane was not <br />detected. Methane was detected at both of the vapor extraction wells (EW-1 and EW-2) <br />at concentrations of 12.5% and 21.7% respectively. At the passive vent pipes (VP-1 <br />through VP-4), methane was detected at concentrations ranging from 0.1% (VP-1) to <br />13.1% (VP-4). Oxygen concentrations at all sample locations ranged from 2.3% (EW-2) <br />and 21.4% (VW-8S). Carbon dioxide concentrations at all sample locations ranged from <br />0.1% (VW-1 and VW-8S) and 29.3% (EW-2). <br /> <br /> <br />CONCLUSIONS AND RECOMMENDATIONS <br /> <br />Since the installation of the passive soil vapor extraction trench in 2006, methane <br />concentrations at previously affected monitoring probes have generally remained below <br />5%, with the exception of probes EW-1, EW-2, VP-3, and VP-4. This suggests that the <br />system continues to effectively control methane migration. Methane concentrations <br />measured during the fourth quarter of 2024 were consistent with historical data, further <br />supporting the system's continued performance. <br /> <br />AGI recommends: <br /> <br /> Continued annual monitoring to ensure methane levels remain below regulatory <br />thresholds. <br /> <br /> Regular inspection and maintenance of monitoring infrastructure to ensure <br />accurate data collection. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />