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FORWARD/AUSTIN LANDFILL PERIMETER LANDFILL GAS (LFG) MONITORING PROBE AND ON-SITE STRUCTURE TESTING SECOND QUARTER 2023 INTRODUCTION This letter provides the results of gas monitoring probes (GMP) and on-site structure testing for the second quarter of 2023 (April through June) 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 AND CONCLUSIONS On April 11 and 27, May 11, June 1 and 12, 2023, no methane gas (the combustible component of LFG) in excess of the LEL(5 percent by volume) was detected at any perimeter subsurface compliance GP probe location tested or in excess of 1.25 percent by volume in air at any interior locations or on-site structures. These results indicate that at the time of our testing, the subject site perimeter subsurface GP probes and interiors of on-site structures are in compliance with the requirements of Title 27 CCR. 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. The instrument measures combustible gas concentrations as a percentage 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 probe testing procedures are as follows: • Connect sample tubing and open test valve; observe pressure and record data. • For probes 20 feet deep or less, turn on the sample pump, and observe and record methane, oxygen, and carbon dioxide gas concentrations, when readings have stabilized for 30 seconds. • For probes more than 20 feet deep, turn on the sample pump, extract a minimum of one probe volume, and observe and record methane, oxygen, and carbon dioxide gas concentrations, when readings have stabilized for 30 seconds. • Close the test valve, disconnect sample instruments, and secure the sample location. Forward/Austin Landfill—Second Quarter 2023 www.scsenaineers.com 1