COMPLIANCE INFO_REV.4TH QTR-ANNUAL REPORT 6/26/2025

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Revised Quarterly Monitoring Report – Fourth Quarter/Annual 2024 www.arcadis.com Revised - Forward Landfill 4Q24 Quarterly Mon Report 06262025 8 4.1.1 Leachate Monitoring Leachate samples are collected quarterly at the Site. The LCRS sump monitoring network in MRP Table 25 includes 22 locations (RWQCB 2024a). The LCRS sump monitoring network should have a total of 25 locations, as presented in Table 1 and Figure 4. One of the locations (D-89) was not included in the fourth quarter 2024 sampling event due to the location being under repair (Appendix B). Sump D-93/94 for WMU D-93/94, listed in Table 25 of the MRP, was improperly labeled in the field as D-93/95 and has been labeled as D-93/95 since May 13, 2020 (see location on Figure 4). Referencing the appropriate nomenclature will begin in second quarter 2025. Quarterly leachate monitoring includes the field analyses and laboratory analyses specified in MRP Table 27 (RWQCB 2024a). Leachate monitoring was conducted from December 4 to 6, 2024. Leachate samples from the leachate holding areas of the Site are also analyzed semiannually for dissolved inorganic constituents and metals, as required by the Water Code Section 13267 Order for Technical Reports Regarding Acceptance of Hazardous Waste, Forward Landfill, San Joaquin County (RWQCB 2017b; see Section 3.1). The semiannual laboratory analyses are scheduled for the first and third quarters of the calendar year. The field and laboratory monitoring results for fourth quarter 2024 are summarized in Table 8. 4.1.2 Leachate Collection and Removal System Testing The LCRSs at the Site are tested annually in accordance with MRP Section D.1.a (RWQCB 2024a). In addition, an annual inspection of each sump is performed by Del-Tech, which most recently occurred on November 8 and 9, 2024. Visual inspections of sumps are also performed weekly by Del-Tech. Documentation of this process will be included in the second quarter 2025 monitoring report and ongoing. LCRS continuity test consists of injecting a high-concentration tracer dye into the far side of the LCRS and allowing the liquids to migrate through the unit to settle in the low point of the LCRS sump. The non-toxic tracer dye liquids allow migration to the lowest point of the sump. Once the tracer dye has migrated through the system, it can be extracted and detected from the sump extraction pipe, indicating that a conduit is present through the unit. If excessive liquid is backed up into the drainage layer of the LCRS, the tracer dye will take longer to migrate to the sump. The LCRS at the Site was tested and passed on November 21 and 22 and December 5 and 6, 2024, at the Class II leachate impoundments, WMU F-West and WMU F-North, respectively. The tests indicated that the required connection exists across the LCRS units. 4.1.3 Leachate and Surface Impoundment Monitoring Leachate from the sumps at the Site are pumped to surface impoundment WMU-F (F-North) and WMU-F (F- West) for evaporation. The locations of the surface impoundments are shown on Figure 4. During the fourth quarter 2024, leachate was observed in WMU D-89, D-93/95, WMU D-01N/S, WMU D-02, WMU FU-03, WMU FU-04E/W, WMU FU-05, WMU FU-06, and FU-19W/E, and surface impoundments F-West and F- North. Sampling details are discussed in Section 4.1.1 and results are presented in Table 8. The volume of leachate pumped to each surface impoundment during fourth quarter 2024 is documented in Appendix F and summarized in Table 4-1 below (as required by MRP Table 26 [RWQCB 2024a]). The freeboard in the surface impoundments was measured weekly; the freeboard logs are also included in Appendix F. The