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Environmental <br /> I SCS FIELD SERVICES Consultants & Contractors <br /> April 11, 2023 <br /> File No. 07218279.01 Task 1 <br /> Mr. Joyesh Chandra <br /> County of San Joaquin <br /> Post Office Box 1810 <br /> Stockton, California 95201 <br /> Subject: First Quarter 2023, Perimeter Monitoring Probe Landfill Gas (LFG) Testing at the <br /> Corral Hollow Landfill, Tracy, California <br /> Dear Mr. Chandra: <br /> This letter provides results of gas monitoring probe (GW)testing for the first quarter of 2023 (January <br /> through March) performed by SCS Field Services (SCS). All testing, monitoring protocols and <br /> reporting were performed in general conformance with Title 27 California Code of Regulations (CCR) <br /> Article 6. Briefly,these regulations require that solid waste disposal site owners/operators <br /> implement LFG control or monitoring provisions to ensure that methane gas concentrations in soils <br /> at the property boundary do not exceed the lower explosive limit(LEL, or 5 percent by volume) and <br /> that interiors of on-site structures do not exceed 1.25 percent by volume in air. Below is a summary <br /> of our quarterly monitoring activities. <br /> SUMMARY, CONCLUSIONS AND RECOMMENDATIONS <br /> On March 2, 2023, no methane gas (the combustible component of LFG) in excess of the LEL was <br /> detected at any location tested. These results indicate that at the time of our testing, the subject <br /> site perimeter subsurface monitoring probes were in compliance with the requirements of Title 27 <br /> CCR Article 6. <br /> GAS TESTING INSTRUMENTATION AND METHODS <br /> Testing for methane gas, oxygen gas, carbon dioxide gas and pressure was performed using a Landtec <br /> GEM-5000 Gas Analyzer calibrated to methane gas. This instrument measures combustible gas <br /> concentrations in air directly on either of two scales,the first as percent by volume of the lower <br /> explosive limit(LEL) of methane gas in air(0 to 5 percent);the other as percent by volume (0 to 100 <br /> percent) in the gas sampled. The detection limit for this instrument is approximately 0.10 percent by <br /> volume. <br /> Gas monitoring well testing procedures are as follows: <br /> • Connect sample tubing, open test valve, observe pressure, and record data. <br /> • For probes 20 feet deep or less,turn on sample pump, observe and record methane, <br /> oxygen, and carbon dioxide gas concentrations, when readings have stabilized for 30 <br /> seconds. <br /> 4730 Enterprise Way, Suite A Modesto, CA 95356 1 209-545-8490 co, <br />