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16 January 2025 <br />Project No. 24-7860 <br />Page 2 of 4 <br />probes (VW-5 through VW-8) were installed to provide additional data on methane <br />concentrations and subsurface gas migration patterns. <br /> <br />Quarterly monitoring conducted by URS in early 2005 revealed methane concentrations <br />exceeding 5% at monitoring locations along the northwestern site boundary, specifically <br />at VW-4, VW-5S, VW-5D, VW-6S, and VW-6D. To address these elevated <br />concentrations, URS installed two soil vapor extraction wells (EW-1 and EW-2) and two <br />additional gas migration monitoring probes (VW-9 and VW-10) in June 2005. <br /> <br />In December 2005, URS conducted a vapor extraction pilot test to evaluate the feasibility <br />of installing a permanent landfill gas extraction system. During this test, vapor samples <br />collected from the extraction wells were analyzed for volatile organic compounds (VOCs). <br />Although VOCs were detected, their total concentrations were below 5 ppmv, indicating <br />minimal risk of significant groundwater impacts. <br /> <br />To mitigate off-site methane migration, a passive soil vapor extraction trench and four <br />vent pipes (VP-1 through VP-4) were installed in September 2006. Since the installation <br />of this system, methane concentrations at the monitoring probes have remained below <br />the regulatory threshold of 5%. <br /> <br />In June 2006, three groundwater monitoring wells were installed at the site to assess <br />potential VOC impacts on groundwater. Analytical results over four quarters indicated <br />stable VOC concentrations below established regulatory levels. In May 2007, the Central <br />Valley Regional Water Quality Control Board (CVWB) approved the suspension of <br />groundwater monitoring activities, citing consistent results and minimal groundwater <br />contamination risk. The groundwater monitoring wells were decommissioned in <br />December 2011. <br /> <br />In April 2011, URS recommended reducing methane monitoring frequency from quarterly <br />to annually, as concentrations at all monitoring probes had remained below the 5% <br />threshold since the installation of the passive vapor extraction system. SJCEHD approved <br />this recommendation, and monitoring activities have since been conducted annually <br />during the fourth quarter. <br /> <br />On 09 May 2024, World Enterprises acquired the property from RS Legacy Corporation. <br />In November 2024, World Enterprises contracted AGI to perform the required annual <br />monitoring activities for the site. During a routine inspection, SJCEHD identified a <br />blockage in vent pipe VP-4, rendering it non-functional. As part of the 2024 annual <br />monitoring event, AGI successfully cleared the blockage and restored VP-4 to operational <br />status. <br /> <br /> <br />ANNUAL FIELD MONITORING ACTIVITIES <br /> <br />On 24 December 2024, AGI measured landfill gas concentrations (i.e., methane, oxygen,