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 6 2.3.2 Quarterly Results Analytical results for the fourth quarter 2024 surface water monitoring are provided in Table 6. No discharges from the Site into the adjacent creeks were observed during fourth quarter 2024. The north and south forks of Little John’s Creek were dry upon initial monitoring on December 6, 2024; therefore, surface water samples could not be collected from any of the monitoring points during fourth quarter 2024. Cumulative data for the four surface water monitoring points for 2024 are included in Appendix D. 3 Corrective Action Monitoring Program This section describes the corrective action monitoring conducted during fourth quarter 2024 associated with the Site and provides the associated monitoring results. Corrective action monitoring is conducted in accordance with MRP Section C (RWQCB 2024a). 3.1 Groundwater Corrective Action Supplemental monitoring of select wells and leachate sumps is required by Water Code Section 13267 Order for Technical Reports Regarding Acceptance of Hazardous Waste, Forward Landfill, San Joaquin County (RWQCB 2017b). As required by MRP Section C.1 and Table 17 (RWQCB 2024a), leachate sumps FU-04E/W, FU-06, FU-17, FU- 19, and FU-23 are analyzed for dissolved inorganic constituents and metals semiannually in first and third quarters. Sump FU-17, listed in Table 25 of the MRP, consists of two temporary sumps, TS-3 and TS-4. These locations were inaccessible and then were relocated in fourth quarter 2024 during the construction of waste management unit (WMU) FU-24. Temporary sumps TS-3 and TS-4 are now sumps for WMU FU-24 (see locations on Figure 4). Sump FU-23 is listed in Table 25 of the MRP; however, this location does not exist for WMU FU-23. Two temporary sumps, TS-1 and TS-2, as shown on Figure 4, are the sump monitoring points for WMU FU-23. As required by MRP Section D.1.e (RWQCB 2024a), the supplemental groundwater monitoring also includes quarterly analysis of dissolved inorganic constituents and metals at monitoring wells AMW-1, AMW-2, AMW-4, and AMW-7. The results of these supplemental analyses for fourth quarter 2024 are presented in Table 7. 3.2 Unsaturated Zone Corrective Action The MRP, Section C.2 and Table 18, (RWQCB 2024a) requires additional analysis of dissolved inorganic constituents and metals for unsaturated zone lysimeters FU-04, FU-05, FU-06, and FU-10 semiannually (first and third quarters). Lysimeter FU-10 is listed in the MRP’s Unsaturated Zone Corrective Action Monitoring Table (MRP Table 18 [RWQCB 20224a]); however, no historical data exist for this location and it is not included in the previous WDRs Order No. R5-2014-0006 (RWQCB 2014). The inclusion of this sampling location is a typographical error; therefore, the proposed corrective action is for this location to be removed from the MRP in the next revision. All analytical results for the unsaturated zone lysimeters are presented in Tables 5a and 5b.