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4730 Enterprise Way, Suite A Modesto, CA 95356 | 209-545-8490 Environmental Consultants & Contractors October 13, 2023 File No. 07218279.01, Task 2 Mr. Joyesh Chandra County of San Joaquin Post Office Box 1810 Stockton, California 95201 Subject: Third Quarter 2023, Perimeter Gas Monitoring Probe and Structure Roof Vent Landfill Gas (LFG) Testing at the Harney Road Landfill, Lodi, California Dear Mr. Chandra: This letter provides results of perimeter monitoring probes (GW) and structure roof vent testing for the third quarter of 2023 (July through September) performed by SCS Field Services (SCS). All testing, monitoring protocols and reporting were performed in general conformance with Title 27 California Code of Regulations (CCR) Article 6. Briefly, these regulations require that solid waste disposal site owners/operators implement LFG control or monitoring provisions to ensure that methane gas concentrations in soils at the property boundary do not exceed the lower explosive limit (LEL, or 5 percent by volume) and that interiors of on-site structures do not exceed 1.25 percent by volume in air. Below is a summary of our quarterly monitoring activities. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS As of the dates of our testing, no methane gas (the combustible component of LFG) in excess of 5 percent by volume was detected at any location tested (i.e., vent risers of structures and perimeter subsurface GW probes). These results indicate that at the time of our testing the subject site perimeter subsurface GW probes and the structure vent risers were in compliance with requirements of Title 27 CCR Article 6. GAS TESTING INSTRUMENTATION AND METHODS Testing for methane gas, oxygen gas, carbon dioxide gas and pressure was performed using a Landtec GEM-5000 Gas Analyzer calibrated to methane gas. This instrument measures combustible gas concentrations in air directly on either of two scales, the first as percent by volume of the lower explosive limit (LEL) of methane gas in air (0 to 5 percent); the other as percent by volume (0 to 100 percent) in the gas sampled. The detection limit for this instrument is approximately 0.10 percent by volume. Gas monitoring well testing procedures are as follows: • Connect sample tubing, open test valve, observe pressure, and record data. • For probes 20 feet deep or less, turn on sample pump, observe and record methane, oxygen, and carbon dioxide gas concentrations, when readings have stabilized for 30 seconds.