COMPLIANCE INFO_Q3 2025 MONITORING REPORT 10-30-25

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Quarterly Monitoring Report – Third Quarter 2025 www.arcadis.com Forward Landfill 3Q25 Quarterly Mon Report 2 x Eight groundwater monitoring wells were installed after the issuance of the MRP (AMW-54R, AMW-60S, AMW-60M, AMW-61M, AMW-61S, AMW-62, AMW-63, and AMW-64) and were added to the groundwater monitoring network. x Four offsite monitoring wells (7833-MW-01 through 7833-MW-04) are monitored quarterly. 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 third quarter 2025 groundwater monitoring event, all the locations in the current groundwater monitoring network were sampled with the exception of two locations (DW-9690 and AMW-52S). Well DW-9690 was not sampled due to the well needing repairs. Well AMW-52S could not be sampled as it was dry. 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 July 29 and August 8, 2025, and collected groundwater samples between July 29 and August 15, 2025. 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 third quarter 2025 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 third quarter 2025 groundwater monitoring event are presented in Tables 3a through 3c. 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