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2025 Annual Corrective Action Evaluation Report <br /> <br />www.arcadis.com <br />Forward Landfill 2025 Annual CA Eval Rpt_08012025(1) 9 <br />- Chloroform concentrations were stable to increasing in wells AMW-50M, AMW-58S, and AMW-60M. <br />Chloroform data from the last 5 years are not available for wells PZ-1 through PZ-3 and CDCR-EW-1 through <br />CDCR-EW-5 because these locations were added to the monitoring program in second quarter 2025. <br />Evaluation of the above chloroform concentration trends and the most recent data indicate the highest and <br />reoccurring concentrations of chloroform are on the offsite CDCR property, with the highest concentrations <br />centered around well AMW-22S. <br />7 Corrective Action Evaluation Summary <br />In accordance with the 2024 MRP Section E.10 (a)(viii) (RWQCB 2024), this section includes a discussion of <br />overall corrective action process and program enhancements. <br />7.1 Corrective Action Evaluation <br />A summary of results compared to the Evaluation Procedures Report (Herst 2002) exceedance criteria (Section <br />3) is as follows: <br /> As shown in Tables 6 through 9, the calculated quarterly TVOC mass during the reporting period ranged <br />from a minimum of 141.5 kg to a maximum of 145.9 kg. There were no exceedances of the mass TL <br />(789.5 kg) during the reporting period. <br /> TVOC mass increased from third quarter 2024 to second quarter 2025 (three consecutive quarters) due <br />to the addition of wells to the monitoring program in fourth quarter 2024 (seven wells) and second quarter <br />2025 (eight wells). Of the additional 15 wells, 12 were placed in the center of the plume mass located on <br />the CDCR property and have TVOC concentrations directly contributing to the increase in TVOC mass <br />during the reporting period. The 2026 Annual Corrective Action Evaluation Report will include the same <br />monitoring well network this report evaluated in second quarter 2025, an update to the corrective action <br />wells under evaluation, and a recalculation of threshold limits. Therefore, the 2026 Annual Corrective <br />Action Evaluation Report will have a more accurate evaluation of the TVOC concentration trends against <br />the current monitoring well network. The annual median TVOC mass increased from 306 to 467 kg during <br />the reporting period (Table 10). Additionally, the calculated TVOC mass for second quarter 2025 is 804.1 <br />µg/L (Table 10). <br /> As shown in Table 11, concentrations of TVOCs in individual wells did not exceed the individual well TLs <br />during the reporting period. <br />Given the Site’s compliance with the three exceedance criteria listed in Section 3, the current corrective action <br />measures ongoing at the Site (Section 2) are effective and will continue to be operated as currently designed at <br />the Site. <br />However, to comply with the CAO, an additional remedial corrective action measure is planned, which will include <br />the installation of a groundwater treatment system and control measures applied to the offsite plume on the <br />CDCR property by groundwater extraction. The installation of this groundwater extraction and treatment system is <br />required to address the outstanding NOV (RWQCB 2023) of the CAO; however, once the system is implemented, <br />it will also serve to satisfy the requirements of the corrective action program.