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Foothill Landfill Landfill Methane Rule (LMR) and New Source Performance Standards (NSPS) Surface Emissions Monitoring Fourth Quarter 2025 INTRODUCTION This letter provides results of the Fourth Quarter 2025 LMR/NSPS surface emissions monitoring (SEM) performed by SCS Field Services (SCS) at the subject site on November 3, 4, 14, 24 and December 4, 2025. All work was performed in accordance with our approved contract dated, November 2018, and LMR requirements. SUMMARY AND CONCLUSIONS As stipulated in the LMR, if no uncorrectable exceedances within the 10-day limitation are detected in the past three years or upon completion of four consecutive compliant monitoring events performed in accordance with the LMR, the landfill may request an exemption from the more stringent monitoring required by the rule and perform monitoring on a 100-foot pathway on an annual basis for closed landfills or quarterly for active disposal sites. Based on the LMR requirements for past regulatory inspection results, the monitoring was performed on a 25-foot pathway. On November 3 and 4, 2025, instantaneous surface emissions testing showed thirty-three (33) exceedances of the LMR/NSPS instantaneous threshold limit of 500 parts per million by volume (ppmv) measured as methane above the background. Based on these monitoring results, corrective actions were taken, and follow-up monitoring was conducted as required. These results are discussed in a subsequent section of this report. In addition, during the instantaneous monitoring event, SCS performed simultaneous integrated monitoring of the landfill surface. As required by the LMR, the landfill was divided into 50,000 square foot areas. The Foothill Landfill surface area was therefore divided into 158 grids, as shown in Figure 1-A in Attachment 1. During the monitoring events, twelve (12) grid areas were observed to exceed the 25-ppmv limit for integrated monitoring. Based on these monitoring results, corrective action was taken and follow-up integrated testing was conducted as required. These results are also discussed in a subsequent section of this report. In addition, quarterly monitoring of the pressurized piping or components of the Gas Collection and Control System (GCCS)that are under positive pressure must be performed quarterly. During this monitoring event, the Landfill Gas (LFG) Blower Flare Station (BFS) was offline and the Power Generation Facility (PGF) was collecting all landfill gas. SCS performed monitoring of the BFS while the system was off line to verify there were no leaks on the flare piping. Further, as required under the LMR, any location on the landfill that has an observed instantaneous methane concentration between 200 and 499 ppmv must be stake-marked and Global Positioning Foothill Landfill—Fourth Quarter 2025 www.scsenaineers.com 1