COMPLIANCE INFO_2025 Q3 CORRECTIVE ACTION

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Brendan Kenny Central Valley Regional Water Quality Control Board October 15, 2025 www.arcadis.com Forward Landfill 3Q25 CAP Update 2/4 Remediation Systems Operations and Performance Summary CAO Task 9.a indicates that quarterly program updates shall include information on remedial systems during each reporting period. A summary of the Site’s GWTS, residential GWTSs, and the facility’s landfill GCCS are provided in this Program Update. Additional details regarding the Site’s GWTS (submitted by October 30, 2025) and the residential GWTSs (submitted by November 1, 2025) are provided under separate cover in the following reports:  Third Quarter 2025 Groundwater Treatment System Monitoring Report; and  Third Quarter 2025 Residential Groundwater Treatment Systems Monitoring Report. Groundwater Extraction and Treatment System A GWTS is operated at the Site to address detections of volatile organic compounds (VOCs) in groundwater in accordance with the WDRs outlined in the Order. The California State Water Resources Control Board Monitoring and Reporting Program (MRP) Table 19 lists six groundwater extraction wells as part of the GWTS (EW-1, EW-2, EW-3R, EW-4, EW-5, and CDCR-EW-1). Five of the six groundwater extraction wells listed in Table 19 of the MRP (EW-1, EW-2, EW-3R, EW-4, and EW-5) are monitored monthly as they are the only extraction wells part of an operational system. Extraction well CDCR-EW-1 is currently not part of an operational remedial system and therefore is not monitored monthly. Additional offsite extraction wells (CDCR-EW-2, CDCR-EW-3, CDCR-EW-4, and CDCR-EW-5) are not included in the MRP and not connected to an operational remedial system and, therefore, are not monitored monthly as part of the corrective action program. However, these five offsite extraction wells were added to the routine quarterly monitoring program in the second quarter of 2025. The extracted groundwater is treated by two 10,000-pound granulated activated carbon (GAC) vessels that were installed in January 2020. During the reporting period, the GWTS was inspected and monitored bi-weekly by Del-Tech Geotechnical Support (Del-Tech) of Oakdale, California. Flow rates from the extraction wells were routinely monitored and adjusted, if needed, to confirm groundwater capture within the treatment area. Del-Tech’s field inspection forms are included in Attachment 1. During the third quarter, the GWTS treated approximately 43,853,289 gallons of extracted groundwater, which represents an average total flow rate of approximately 555,105 gallons per day. Based on the extracted volumes and analytical VOC concentrations, the GWTS removed approximately 0.57 pounds of total VOCs during the reporting period. Del-Tech’s downtime log for the reporting period is included in Attachment 1. The GWTS was operational throughout the reporting period with no significant recorded downtime, except for the following downtime event, which indicates the system was operational for over 99 percent of the time (a total of 1,896 hours of system operation between the beginning of the reporting period through the final visit of the quarter on September 17, 2025):  On September 3, 2025, extraction well EW-4 was momentarily turned off to remove the flow meter as it was not reading accurately, it was restarted shortly after. There is currently no flow meter at EW-4 while the manufacturer repairs the flow meter. It is expected to be replaced during fourth quarter 2025. Low concentrations of total VOCs (up to 1.81 micrograms per liter of total VOCs) were detected in the six system influent samples collected. No VOCs were detected above the practical quantitation limit in any of the system effluent samples collected at the point of compliance, satisfying the discharge requirements of the Order.