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2025 Annual Corrective Action Evaluation Report <br /> <br />www.arcadis.com <br />Forward Landfill 2025 Annual CA Eval Rpt_08012025(1) 6 <br />5.2 Landfill Gas Monitoring Results <br />In accordance with the 2024 MRP Section E.10 (a)(vii) (RWQCB 2024), this section discusses the monitoring <br />data collected from the landfill gas monitoring system and the extraction well network during the reporting period. <br />During the reporting period the landfill gas collection and control system (GCCS) at the Site was monitored by a <br />network of landfill gas extraction wells. The landfill gas collected from these wells is routed and split between <br />two onsite flares (FL-100 and FL-150) and the onsite landfill gas-to-energy plant operated by Ameresco. Flares <br />FL-100 and FL-150 were previously reported as Flare A-2 and Flare A-3, respectively. The landfill GCCS is <br />upgraded routinely to optimize landfill gas collection and reduce the potential for landfill gas impacts in the <br />unsaturated zone through source control measures. <br />The Site includes 27 perimeter landfill gas monitoring probes spaced approximately 1,000 feet apart, pursuant to <br />Title 27 of the Code of California Regulations. These probes include multi-level monitoring of shallow and deep <br />intervals. Several of the probes also include monitoring of a medial interval. Site perimeter gas monitoring <br />probes were monitored quarterly for methane, carbon dioxide, oxygen, balance gas, and static pressure. <br />Quarterly landfill gas sample analytical results for the Site, provided by SCS Field Services and Geosyntec <br />Consultants, are provided in Appendix C. Quarterly results are generally consistent at the Site. Methane was <br />detected at a concentration above 1 percent in three landfill gas monitoring probes during third quarter 2024, <br />three landfill gas probes during fourth quarter 2024, five landfill gas probes during first quarter 2025, and three <br />landfill gas probes during second quarter 2025. <br />Given the general lack of detectable methane above 1 percent in the Title 27 perimeter landfill gas probes <br />during the reporting period, it can be concluded that the GCCS continues to operate effectively. Forward will <br />continue to enhance the GCCS through regular maintenance and adjustments of the landfill gas well field. <br />5.3 Groundwater Treatment <br />The extraction and treatment of groundwater at the site along the POC is a corrective action measure that aims <br />to capture groundwater and prevent the release of groundwater impacts from the Site to hydraulically <br />downgradient areas. <br />In compliance with applicable WDR Order No. R5-2003-0080 (RWQCB 2003), details regarding the Site’s <br />groundwater treatment system are provided in the quarterly groundwater treatment system monitoring reports <br />(Arcadis 2024a, 2025a, 2025c, 2025d, 2025h). The GWTS had no VOC detections and therefore was compliant <br />with WDR Order No. R5-2003-0080 and the 2024 MRP during the monitoring period. Details regarding the <br />residential treatment systems are provided in the quarterly residential groundwater treatment system monitoring <br />reports (Arcadis 2024c, 2025b, 2025e, 2025i). The effluent sample concentration limit for VOCs at each <br />residential treatment system was non-detect during the reporting period. All residential treatment systems were <br />in compliance with this effluent limit during the reporting period.