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Rationale for Considering Conditional - 4 - 25 March 2026 <br /> No Further Action <br /> Olin Chlor Alkali Facility <br /> Tracy, San Joaquin County, California <br /> CC14: Recent analytical results for CC14 are shown in Figures 6 through 8. Time-series <br /> graphs for CC14 in the upper, middle, and lower groundwater zones are plotted in <br /> Figures 12 through 14. Concentrations of CC14 in the upper and lower zone <br /> groundwater monitoring wells are below the MCL of 0.50 pg/L. Concentrations above <br /> the MCL are limited to one well in the middle zone (MW-12). However, one 2024 grab <br /> groundwater sample collected in the lower zone had a CC14 detection above the MCL <br /> (0.80 pg/L). Based on the March 2025 groundwater monitoring event and the June <br /> 2024 step-out investigation, the extent of CC14 is bound to the northeast and south. <br /> The table below presents the most recent concentrations of CC14 measured during <br /> the March 2025 groundwater monitoring event and the June 2024 grab-groundwater <br /> investigation: <br /> Identification Sample CC14 Concentration Sample Type <br /> Number Month/Year p /L <br /> Upper Zone <br /> MW-5 March 2025 0.28 J Well <br /> MW-9 March 2025 <0.025 Well <br /> MW-11 March 2025 <0.025 Well <br /> MW-13 March 2025 <0.025 Well <br /> GGW-1 June 2024 <0.20 Grab <br /> GGW-2 June 2024 0.074 J Grab <br /> Middle Zone <br /> MW-10 March 2025 0.32 Well <br /> MW-12 March 2025 1.3 / 1.3 Well <br /> MW-14 March 2025 <0.025 Well <br /> GGW-1 June 2024 <0.20 Grab <br /> GGW-2 (37.5) June 2024 0.040 J / 0.038 J Grab <br /> GGW-2 (51) June 2024 0.16 J Grab <br /> Lower Zone <br /> MW-15 March 2025 0.25 Well <br /> GGW-1 June 2024 <0.20 Grab <br /> GGW-2 June 2024 0.80 Grab <br />