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Transformer Oil Release Clean-up and Closure Report 1049 South Wilson Way, Stockton California The current (June 2020— Revised May 2022) DTSC-Modified SL for Aroclor 1260 in Residential Soil (Cancer Endpoint) is 0.24 milligrams per kilogram (mg/kg). Aroclor 1260 was detected in one soil sample at a concentration above the applicable SL of 0.24 mg/kg. The Aroclor 1260 concentration in the GV15 sample was 0.47 mg/kg. Aroclor 1260 was detected in 12 other soil samples, but at concentrations below the applicable SL of 0.24 mg/kg. In five of these samples (GV8, GV9, GV14, GV19, and GV20), Aroclor 1260 was detected at concentrations above the laboratory reporting limit; the maximum concentration was 0.19 mg/kg in the GV19 sample. In the seven remaining samples (GV1, GV2, GV11, GV12, GV17, GV18, and L1), Aroclor 1260 was detected at estimated ("J-flagged") concentrations at or below the laboratory reporting limit of 0.050 mg/kg. Aroclor 1260 was detected in the Phase 2 concrete sample (SDI) collected inside the storm drain, at a concentration of 9.9 mg/kg. Aroclor 1260 was also detected in the associated duplicate concrete sample, at a concentration of 12 mg/kg. Aroclor 1260 was detected in the Phase 2 wipe sample (W2) collected inside the storm drain, at a concentration of 1.6 micrograms per 100 square centimeters (pg/100 cm2). 2.4 Phase 3 2.4.1 Phase 3 Excavation September 4, 2021 - PG&E returned to the site and conducted further excavation (Figure 2). Additional excavation was conducted at location GV15, to a depth of approximately 3 ft bgs, due to the Aroclor concentration reported in the Phase 2 sample from this location (Section 2.3.2). Excavation was also conducted, to a depth of approximately 0.67 ft bgs, in a driveway at the 1049 South Wilson Way property, to the south of the transformer pole. 2.4.2 Phase 3 Verification Sampling and Results September 4, 2021 - After the excavation was completed, Arcadis returned to the site and collected verification samples within the excavated area. Arcadis collected a soil sample from the base of the Phase 3 excavation at location GV15. A duplicate soil sample was also collected at this location. Arcadis collected eight soil subsarnples from the driveway area, which were then composited into two samples for analysis, using a 4-point subsample grid for each composite. The two 4-point subsample grid locations were designated as: Ll A through L1D (analyzed as L1-Comp) and M1A through M1D (analyzed as M1-Comp). All samples were placed in ice-chilled coolers and transported under proper chain of custody protocol to Castle for PCB analysis by USEPA Method 8082. The analytical results are summarized in Table 1. No PCBs were detected in the Phase 3 verification samples. arcadis.com Stockton Release Closure Report 07062022 5