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Quarterly Monitoring Report— First Quarter 2026 AMW-10 was erroneously reported as unable to be sampled due to needing repairs. The 2025 audit confirmed the well has been abandoned in place. For evaluation purposes, the groundwater monitoring wells at the Site have been divided into three groups based on the depth of the screened interval (shallow, intermediate, and deep). Shallow wells are screened predominantly at elevations greater than -50 feet relative to mean sea level (MSL). Intermediate wells are screened predominantly at elevations of-50 to-125 feet relative to MSL. Deep wells are screened predominantly at elevations below-125 feet relative to MSL. During the first quarter 2026 groundwater monitoring event, all the locations in the current groundwater monitoring network were sampled. Supplemental analyses are conducted every 5 years. The next 5-year analyses will be conducted in third quarter 2028 (MRP Table 4 [RWQCB 2024]). 2.1.2 Field Activities Quarterly sampling was conducted in accordance with the Sampling and Analysis Plan, as provided in Appendix A, and the MRP (Section B.1 and Tables 2 and 3; RWQCB 2024). Well monitoring was conducted by Del-Tech Geotechnical Support Services (Del-Tech), located in Oakdale, California. Del-Tech collected depth-to- water(DTW) measurements at all monitoring wells between January 27 and February 6, 2026, and collected groundwater samples between January 28 and February 10, 2026. DTW measurements were collected at each well before purging and sampling; field records are provided in Appendix B. The groundwater elevation data for the Site are summarized in Table 2, and a groundwater elevation contour map is provided as Figure 8. Groundwater in the vicinity of the Site generally flowed towards the northeast, with an average hydraulic gradient of approximately 0.002 foot per foot and an average flow rate of approximately 2.0 feet per day (730 feet per year) (MRP Table 5 [RWQCB 2024]). Following gauging activities, the wells were purged and groundwater samples were collected. The samples were submitted to Pace Analytical Environmental Services, located in Bakersfield, California, a state-certified laboratory. The first quarter 2026 samples were analyzed for routine physical parameters (i.e., turbidity, temperature, specific conductance, and pH) as stipulated in MRP Table 2 (RWQCB 2024) and constituent parameters as stipulated in MRP Table 3 (RWQCB 2024). Field data sheets are provided in Appendix B. Laboratory analytical reports and chains-of-custody documentation are provided in Appendix C. 2.1.3 Analytical Results Laboratory analytical results from the first quarter 2026 groundwater monitoring event are presented in Tables 3a through 3c, and Table 4. The volatile organic compound (VOC)data presented in the tables include results greater than the laboratory practical quantitation limit (PQL); estimated (J-qualified)VOC data between the PQL and the laboratory method detection limit(MDL) are also included to evaluate exceedances. Cumulative data for all groundwater monitoring points and constituents for the past year(first quarter 2025 through first quarter 2026) are included in Appendix D. www.arcadis.com Forward Landfill 1Q26 QMR 2