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Rutan & Tucker, LLP 13 July 2023 Page 3 comply with MM 4.8-2a of the DEIR prepared for the Tracy Hills Project. The collected soil vapor samples were analyzed for fixed gases (oxygen, carbon dioxide, and methane) using ASTM Method 1946D. These activities were performed in general accordance with the DTSC Soil Gas Advisory. Methane was not detected in the soil vapor samples collected from any of the 12 probes. CORRAL HOLLOW LANDFILL The Corral Hollow Landfill is a closed municipal (aka California Class Ill) landfill with an active landfill gas collection system. This landfill has an established Closure and Post Closure Maintenance Plan being implemented by the San Joaquin County Department of Public Works Solid Waste Division (County) and overseen by the Central Valley Regional Water Quality Control Board. This landfill stopped receiving waste in 1991 and its final cover was constructed in 1995. The active landfill gas collection system began operation in December 2001. Routine operation, maintenance, and monitoring activities have been conducted at this landfill, which included some corrective actions to improve and fine tune the effectiveness of the landfill gas collection system. Currently, this system contains 53 landfill gas extraction wells connected to a flare. Quarterly monitoring is being performed at the Corral Hollow Landfill, which includes collecting samples from nine landfill gas monitoring wells located around Its perimeter, CHL -GW -1 through CHL -GW -9.1 Quarterly monitoring for fixed gases (oxygen, carbon dioxide, and methane) began in 2006, with three samples collected within the wells, shallow, middle, and deep, and measured using a calibrated field meter. Methane has consistently been detected at 0 percent, with the occasional 0.1 percent, in all but one location. Perimeter gas monitoring well CHL -GW -6 initially detected a methane concentration of 5.2 percent, however, starting in April 2014 methane concentrations of 0 percent, with the occasional 0.1 percent, have been consistently detected. In the March 2023 quarterly monitoring event, the most recent event reported, no methane concentrations were detected in any of the landfill's nine perimeter gas monitoring wells. Three of these gas monitoring wells, CHL -GW -1, CHL -GW -2, and CHL -GW -3, are located along the northwest perimeter, between the Corral Hollow Landfill and the adjacent Tracy Hills Phases 2, 3, and 4 property. Methane Migration Haley & Aldrich understands San Joaquin County Environmental Health Division (EHD) has identified a concern with the potential migration of methane from the Corral Hollow Landfill and the City of Tracy Landfill to adjacent properties under development by ICGC and Lennar. Based on the methane data presented above, there is no evidence that methane is presently migrating, or is likely to migrate in the future from either of these two landfills towards the Tracy Hills Phases 2, 3, and 4 property or 30600 Corral Hollow Road/KT Property/Hillview. 1 CHL -GW -08 and CHL -GW -09 are not included on Figure 1 as their locations were not provided in the referenced report.