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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) 4 <br />the addition of wells to the monitoring program in fourth quarter 2024 (seven wells) and second quarter 2025 <br />(eight wells). Of the additional 15 wells, 12 were placed in the center of the plume located on the California <br />Department of Corrections and Rehabilitation (CDCR) property, and these wells have TVOC concentrations that <br />directly contributed to the increase in TVOC mass during the reporting period. The annual median TVOC mass <br />increased from 306 to 467 kg during the reporting period (Table 10). <br />The TVOC mass is largely driven by the concentrations of VOCs in monitoring well AMW-22S, which are largely <br />driven by carbon tetrachloride, with additional detections of chloroform and tetrachloroethene (PCE). These <br />carbon tetrachloride and chloroform detections do not occur in the wells closest to the Site and may be associated <br />with offsite sources. Other significant contributors to the TVOC mass include monitoring wells AMW-50M (carbon <br />tetrachloride and PCE), AMW-58S (carbon tetrachloride and chloroform), AMW-60M (carbon tetrachloride and <br />PCE) and, more recently, CDCR property wells CDCR-EW-1 through CDCR-EW-5 (TCE, cis-1,2-dichlorothene <br />[cis-1,2-DCE] and chloroform) and PZ-1 through PZ-3 (carbon tetrachloride and PCE). <br />The distribution of carbon tetrachloride and chloroform near well monitoring AMW-22S has been further <br />delineated by the recent installation of several nearby wells, as follows: <br /> AMW-58S, AMW-58M, AMW-59S, and AMW-59M were added to the monitoring program beginning in third <br />quarter 2024. <br /> AMW-60S, AMW-60M, AMW-61S, and AMW-61M were added to the monitoring program beginning in fourth <br />quarter 2024. <br /> CDCR-EW-1 through CDCR-EW-5 and PZ-1 through PZ-3 were added to the monitoring program beginning <br />in second quarter 2025. <br />The inclusion of the above additional wells on the CDCR facility and analytical results indicate carbon <br />tetrachloride and chloroform occur in these wells, located near monitoring well AMW-22S, at higher <br />concentrations than previously mapped, and this change has resulted in an increase in TVOC mass for second <br />quarter 2025. The calculated TVOC mass for second quarter 2025 is 804.1 µg/L (Table 10). <br />In addition, trichloroethene (TCE) has been detected in wells at the 7833 Newcastle Road residence, to the north <br />of the Site. This TCE occurrence appears to represent a separate localized offsite source and is not addressed in <br />this report. <br />4.3 Individual Well TVOC Concentrations <br />In accordance with the 2024 MRP Section E.10 (a)(iii) (RWQCB 2024), this section discusses individual well <br />TVOC concentrations at the Site. <br />The TVOC concentrations observed at individual wells for the reporting period are presented in Tables 2 through <br />5 and summarized on Table 11. Time-series charts for TVOC mass and individual well TVOC concentrations, and <br />a historical database summary, are presented in Appendix B. <br />The individual TVOC concentrations for each quarter (as required by 2024 MRP Section E.10(a)(iii)) were <br />compared to the established TVOC concentration TLs. As shown in Table 11, no individual well TL exceedances <br />occurred during the reporting period.