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Transformer Oil Release Clean-up and Closure Report 1049 South Wilson Way, Stockton California 1 Introduction On behalf of Pacific Gas and Electric Company (PG&E), Arcadis U.S., Inc. (Arcadis) prepared this Transformer Oil Release Clean-up and Closure Report (Report) for the oil release incident that occurred on July 27, 2021, near 1049 South Wilson Way in Stockton, California. The release occurred at approximately 1:30 a.m. from a PG&E pole-mounted transformer located adjacent to the street, near the northeastern corner of the property located at 1049 South Wilson Way, in the City of Stockton, California (site; Figures 1 and 2). PCB-containing oil was commonly used as a dielectric fluid in various electrical components until 1979, when it was banned from use in newly manufactured equipment. Non-PCB-containing mineral oil was typically used in electrical transformers after the 1979 regulation, but older PCB-containing transformers are still in service. Aroclor is a commonly known trade name for PCB mixtures that were produced from the 1930's until 1979; Aroclors are often found in pre-1979 transformers. This Report summarizes the emergency response activities conducted during the first 24 hours following the release incident, and the follow-up excavation, and clean-up verification sampling events implemented at the location of the release. PG&E performed this remedial work under United States Environmental Protection Agency (USEPA) oversight, in coordination with the California Governor's Office of Emergency Services (Cal OES). 2 Incident Summary This section provides a summary of the incident response, excavations, clean-up and verification sampling activities conducted on July 27, 2021, through March 31, 2022. PG&E communicated emergency spill response and clean-up activities to the Cal OES, and to San Joaquin County Environmental Health as the Certified Unified Program Agency (CUPA), on July 27, 2021, at 12:00 p.m. PG&E, Hydrochem PSC (PSC), Ancon Services (Ancon) subcontracted by PSC, Ponder Environmental Services (Ponder), and Arcadis performed incident response activities, including initial emergency response, excavation clean-up activities, and verification sampling. Castle Analytical Laboratory of Atwater, California (Castle; California Environmental Laboratory Accreditation Program [CA ELAP] #2480) and Excelchem Laboratories of Rocklin, California (Excelchem; CA ELAP #2110) provided analytical services. The site, approximate location of the power pole/transformer, excavation boundaries, verification sampling locations, and analytical results are shown on Figure 2. Analytical results are presented in Tables 1 and 2. Laboratory analytical reports and chain of custody documentation are included as Appendix A. A photograph log of remedial activities is included as Appendix B. After the initial emergency response (Section 2.1), four phases of clean-up and verification sampling were conducted. The first phase occurred between July 27 and August 11, 2021 (Section 2.2). The second phase occurred on August 28, 2021 (Section 2.3). The third phase occurred on September 4, 2021 (Section 2.4). The fourth and final phase occurred between March 23 and 31, 2022 (Section 2.5). The four phases of clean-up and verification sampling are presented on Figure 2. All wastes were subsequently removed from the Site (Section 2.6). arcadis.com Stockton Release Closure Report_07062022 1