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Mr. Todd Del Frate -2- <br />Foothill Sanitary Landfill <br /> <br /> <br /> <br />All four lysimeters were dry during the first semiannual monitoring event. <br />Methane was detected at four internal monitoring points (soil gas well SG-01 at 0.2%-vol, and <br />SG-02AS, SG-11AD and SG-11AS at 0.1%-vol) during the January 2025 sampling event and in <br />six monitoring points (SG-1, SG-2AD, SG-6AD, SG-6AI, SG-6AS, and SG-9) during the May <br />2025 sampling event at concentrations ranging from 0.1 to 0.3%-vol. Methane was not reported <br />in the perimeter soil gas locations during January 2025. Low concentration methane was <br />reported in multiple perimeter soil gas locations during May 2025 but these detections are <br />believed to be the result of a meter calibration issue. <br />I certify under penalty of perjury that I am familiar with the information submitted in this report, <br />and to the best of my knowledge the report is true, accurate, and complete. <br /> <br />If you have any questions, please contact me at (209) 953-7316. <br /> <br /> <br />Sincerely, <br /> <br /> <br />Mark Houghton <br />Senior Engineer <br />Enclosure <br /> <br />cc: (Via Email): David Toliver, Deputy Director/Operations <br /> Bryce Howard, Integrated Waste Manager <br /> Natalia Subbotnikova, Environmental Health Department <br /> <br />N:\1Foothill\RWQCB\Groundwater Monitoring\2025 GW Reports\1st Semi-annual\Foothill 1st SA 2025 <br />CL.doc