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Rationale for Considering Conditional - 6 - 25 March 2026 No Further Action Olin Chlor Alkali Facility Tracy, San Joaquin County, California MW-15 March 2025 11 Well GGW-1 June 2024 0.12 J Grab GGW-2 June 2024 71 Grab - Laboratory J flag indicates an estimated value. - Groundwater samples were analyzed for VOCs by USEPA Method 8260D. - Middle zone grab groundwater samples GGW-2 were collected at 37.5 and 51 feet bgs. - The primary and duplicate samples where collected are separated by a forward slash. < = CF not detected above the method detection limit. Mann-Kendall Test: Mann-Kendall analyses were performed on the data collected from historical groundwater monitoring wells. A 90 percent confidence level was used to assess the presence of a concentration trend for a given analyte at a given well. The results of the Mann-Kendall trend analysis and summary statistics are shown in Table 1, and the Mann-Kendall results are summarized below: • CC14 (five analyte-well combinations analyzed): o Four wells (MW-5, MW-10, MW-12, and LM151 B) show decreasing trends. o One well (MW-15) shows no trends. • CF (12 analyte-well combinations analyzed): o Four wells (MW-6, MW-10, MW-11, MW-12) show decreasing trends. o Six wells (MW-1, MW-2, MW-5, MW-7, MW-9, and AP-2) show no trend. o Two wells (MW-3 and MW-15) show increasing trends. Although increasing trends are shown for CF at MW-3 and MW-15, the following observations are noted: • While MW-3 shows an increasing trend based on data between well installation in 1989 and the well going dry in 2018, over the more recent and representative period of 2010 to 2018, CF shows a decreasing trend. Between 2010 and 2018, CF concentrations decreased from 170 pg/L in September 2010 to 33 pg/L in September 2017 (Figure 15). • In well MW-15, the highest historical CF concentration was 23 pg/L (detected in August 2012; Figure 17), which is below the MCL of 80 pg/L. Recent concentrations are within the historical range of detections and below 23 ug/L. Linear Regression Analysis: A linear regression analysis was conducted on the CC14 in MW-12 to estimate the time to reach the MCL. Based on data collected between 2015 and 2025, the concentration of CC14 is projected to decrease to below the MCL of 0.5 pg/L by approximately 2035.