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2025 Annual Corrective Action Evaluation Report
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<br />www.arcadis.com
<br />Forward Landfill 2025 Annual CA Eval Rpt_08012025(1) 7
<br />6 Comparison of Current to Historical Groundwater
<br />Quality
<br />The 2024 MRP Section E.10 (a)(iv) requires a comparison of groundwater monitoring results over time for each
<br />contaminant of concern (COC) by well (RWQCB 2024). Appendix D includes time-series plots for each well with
<br />the primary site COCs (PCE, TCE, cis-1,2-DCE, carbon tetrachloride, and chloroform) observed across the
<br />groundwater monitoring well network presented over the last 5 years. The results for the primary site COCs
<br />during second quarter 2025 are discussed in this section, as well as the concentration trends across the previous
<br />5 years (Appendix D). Figures showing the distribution of primary site COCs across the reporting period can be
<br />found in the quarterly monitoring reports for third quarter 2024 through second quarter 2025 (Arcadis 2024c,
<br />2025e, 2025f, 2025i).
<br /> PCE concentrations equaled or exceeded 1 µg/L at domestic supply wells 7898-A and 8106-A and in
<br />groundwater monitoring wells AMW-13, AMW-18B, AMW-22, AMW-22S, AMW-23M, AMW-24R, AMW-25,
<br />AMW-26R, AMW-29S, AMW-29, AMW-30, AMW-31, AMW-44, AMW-45, AMW-46, AMW-50S/M, AMW-51M,
<br />AMW-52S/M, AMW-54R, AMW-56, AMW-58S/M, AMW-59M, AMW-60S/M, AMW-61S/M, AMW-63, PZ-1
<br />through PZ-3, and CDCR-EW-1 through CDCR-EW-5. The highest concentration of PCE was measured at
<br />18 µg/L in well CDCR-EW-4. Where the data are available, PCE concentration trends across the last 5 years
<br />(Appendix D) are as follows:
<br />- PCE concentrations have decreased in wells AMW-13, AMW-26R, and AMW-31.
<br />- PCE concentrations have remained relatively stable in wells AMW-22, AMW-22S, AMW-29, AMW-44,
<br />AMW-45, AMW-46, AMW-50S, AMW-51M, AMW-52S, AMW-54R, AMW-56, AMW-59M, AMW-60M,
<br />AMW-61M, and AMW-63.
<br />- Concentrations of PCE have been stable to increasing in wells AMW-18B, AMW-23M, AMW-24R, AMW-
<br />25, AMW-29S, AMW-30, AMW-50M, AMW-52M, AMW-58S/M, AMW-60S, and AMW-61S.
<br />PCE 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 PCE concentration trends and the most recent data indicate the highest and
<br />reoccurring concentrations of PCE are on the offsite CDCR property, with the highest concentrations centered
<br />around well AMW-22S. There is an additional plume with lower concentrations at the landfill centered around
<br />AMW-63.
<br /> TCE concentrations equaled or exceeded 1 µg/L at groundwater monitoring wells AMW-22S, AMW-22, AMW-
<br />23M, AMW-24R, AMW-29, AMW-46, AMW-50M, AMW-51M, AMW-52S, AMW-54R, AMW-56, AMW-58S/M,
<br />AMW-60S/M, AMW-61M, AMW-63, PZ-1 through PZ-3, and CDCR-EW-1 through CDCR-EW-5. The highest
<br />concentration of TCE was measured at 11 µg/L in well AMW-22S. Where the data are available, TCE
<br />concentration trends across the last 5 years (Appendix D) are as follows:
<br />- TCE concentrations have decreased in AMW-29.
<br />- TCE concentrations have remained stable at wells AMW-22, AMW-22S, AMW-23M, AMW-46, AMW-51M,
<br />AMW-54R, AMW-56, AMW-58M, AMW-61M, and AMW-63.
<br />- TCE is stable to increasing in wells AMW-24R, AMW-50M, AMW-52S, AMW-58S, and AMW-60S/M.
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