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(estimated concentrations below the reporting limit) in Upper Horizon wells MW-5, MW-11, MW-13,and MW-14.Carbon tetrachloride was not detected at any other monitoring wells during this reporting period (Table 6 and Figures 8 and 9). Carbon tetrachloride concentrations reported for the March 2023 sampling events are consistent with the previous declining concentration trend. Carbon tetrachloride concentrations detected since February 2005 are plotted on Figures 10,11,and 12 for the Upper, Middle,and Lower Horizons, respectively. Historical carbon tetrachloride concentrations are shown on Figure D-1 and tabulated in Table D-1,Appendix D. Chloroform Chloroform was detected in samples collected from monitoring wells MW-5, MW-9, MW-10, MW-11, MW-12,and MW-15 during the March 2023 sampling event.Concentrations of chloroform ranged from 2.7 to 76 pg/L in these wells(Table 6). No wells exceeded the California MCL of 80 Ng/L. Results are shown in Table 6 and Figures 13 and 14. Chloroform concentrations in the Upper Horizon well MW-9 and Lower Horizon well MW-15 increased since the previous sampling event, however, concentrations at both MW-9 and MW-15 remain below the California MCL of 80 Ng/L.Chloroform concentration in the Middle Horizon well MW-12 decreased to below the California MCL for the first time since 2011. Chloroform concentrations reported for the remaining March 2023 samples are generally consistent with previous results.Chloroform detections since February 2005 are plotted on Figures 15,16,and 17 for the Upper, Middle,and Lower Horizons, respectively. Historical chloroform concentrations are shown on Figure D-2 and tabulated in Table D-1,Appendix D. Other VOCs The following VOCs were identified below their reporting limit:l,1- dichloroethane;V-dichloroethene;1,2-dichloropropane; and chloromethane. Detections of these VOCs are estimated values because they are below the laboratory reporting limit but above the maximum detection limit. None of these VOCs were detected above their respective Water Quality Goal (Table 6). TCE has been detected in MW-15 since 2005 and MW-16 from 2009-2021 at levels below the California MCL.TCE was also detected below the MCL in MW-12 in 2021.The most recent March 2023 sampling event detected TCE in MW-10 and MW-12 at concentrations below the laboratory reporting limit and at MW-9 slightly above the reporting limit. TCE concentrations detected since 2005 are shown on Figure 18 for the Lower Horizon. Historical TCE concentrations are tabulated in Table D-1, Appendix D. No other VOCs were detected. Historical VOC concentrations are tabulated in Table D-1,Appendix D. VOC Trend Summary https://woodplc.sharepoint.com/teams/olintracy/shared documents/general/03.0 docctrl/2021 biennial report/01_text/tcy 2021 biennial_text_rev.docx Page 5