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Revised Quarterly Monitoring Report – <br />Fourth Quarter/Annual 2024 <br />www.arcadis.com <br />Revised - Forward Landfill 4Q24 Quarterly Mon Report 06262025 13 <br /> CNSDAM evaluation of the environmental monitoring results for the Site from fourth quarter 2024 indicates <br />that monitoring wells AMW-6, AMW-12, MW-2A, MW-10, and MW-19R are to be resampled during first <br />quarter 2025 as a result of one or more VOC detections (Tables 3a through 3c). In a letter dated January 30, <br />2025, the RWQCB was notified of these exceedances (Forward 2025c). <br /> There were no exceedances above CLs for inorganic constituents during fourth quarter 2024. <br /> Analytical results from site monitoring wells during fourth quarter 2024 are consistent with historical trends. <br /> No surface water samples were collected from surface water monitoring stations during fourth quarter 2024. <br /> For unsaturated-zone monitoring stations, one suction lysimeter (LY-POND-N) contained sufficient liquid for <br />analyses of VOCs (Table 5a). No VOCs were detected from the lysimeter sample collected. The sample did <br />not contain sufficient liquid for analysis of inorganic parameters. <br />6 Summary – Annual <br />An annual monitoring report is required as stated in MRP Section E.2 (RWQCB 2024a). <br />During the 2024 monitoring year, groundwater elevations and groundwater and surface water sampling was <br />performed quarterly at the Site. The groundwater and surface water samples were analyzed for the monitoring <br />parameters required by the MRP (RWQCB 2024a), and a summary of the 2024 Sampling and Analysis Plan is <br />provided in Appendix A. <br />6.1 Detection Monitoring Program Results <br />Groundwater monitoring and corrective actions conducted throughout 2024 are in accordance with MRP Sections <br />B and C (RWQCB 2024a). <br />6.1.1 Groundwater Monitoring <br />Groundwater elevations measured during 2024 were variable, reflecting seasonal precipitation patterns. During <br />2024, groundwater flow was generally orientated towards the northeast. For each groundwater monitoring well, <br />hydrographs presenting historical groundwater elevations are included as Appendix E-2 (as required by MRP <br />Section E.2.e [RWQCB 2024a]). The hydrographs present the groundwater elevations with respect to the top and <br />bottom of the screened interval and the elevation of pump intake. The groundwater elevation data on the <br />hydrographs indicate generally static trends. <br />Groundwater elevation maps for first through third quarters 2024 were previously submitted by Arcadis (2024f, <br />2024g, 2024k). The groundwater elevation contour map for fourth quarter 2024 is included as Figure 8. <br />Groundwater quality conditions beneath the Site during 2024 are generally similar to those observed during 2023. <br />Time-series plots of VOC and inorganic constituent concentrations for monitoring wells, including all historical <br />data, are included in Appendix E-3. Piper diagrams are also included in Appendix E-3 and display a cation/anion <br />balance for monitoring well locations throughout 2024. The cation/anion balance in the piper diagrams was <br />evaluated for inorganic constituents at the Site (magnesium, calcium, sodium-potassium, sulfate, chloride, <br />carbonate-bicarbonate). The cation/anion balance ranged from 3.9 to 6.8% throughout 2024.