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1111 Broadway,61 Floor Geosyntec Oakland,California 94607 PH 510.836.3034 consultants www.geosyntec.com Memorandum Date: September 6, 2024 To: San Joaquin County Environmental Health Department Copies to: Phil Simon(Stockton Fire Department), Jason Cashman (Port of Stockton) Subject: Investigation Work Plan, Shed 7 UST Geosyntec Consultants, Inc. (Geosyntec) has prepared this Investigation Work Plan, Shed 7 UST (Work Plan) on behalf of the Port of Stockton regarding the former underground storage tank (UST) located on Port Road 4, Port of Stockton (the Port) (Figure 1). This Work Plan describes the proposed field activities to permit closure in place(CIP) of the former UST in accordance with San Joaquin County Environmental Health Department(SJCEHD) guidelines. 1. SITE BACKGROUND The UST is located adjacent to the eastern edge of Shed 7 at the Port. Shed 7 is currently used for equipment storage and is located adjacent to a shipping loading/unloading area used for Port operations. The UST is positioned between rail lines to the east and Shed 7 to the west(Figure 2). On a 1954 plan drawing, the UST area is labeled as a "10,000 Gal. oil tank under platform;" this drawing is the only known documentation of this UST. The historical plan drawing that identified the oil tank also shows that Shed 7 was used as a warehouse that included a boiler used for heating. For this reason,the former UST is suspected to have contained heating oil.Based on available Port records, no unauthorized releases from the tank have been documented. 1.1 Initial Investigation On July 16, 2024, the UST access manhole was reported to the Port as a "manhole" after being encountered by contractors working on utility and building foundation repairs at Shed 7. The UST access manhole is located where the platform adjacent to Shed 7 was partially demolished as part of the recent construction(Photograph 1). The floor of Shed 7 is approximately 3.5 feet above the top of the UST access manhole, and the remaining parts of the platform extend laterally from the building floor and over portions of the UST (Attachment A). On July 30, 2024,the Port and Geosyntec located and reviewed the historical plan drawing,which revealed the potential for the "manhole" to be a UST. On July 31, 2024, SJCEHD and Stockton Fire Department were notified of the UST finding. Geosyntec conducted site visits on August 7 and August 15, 2024, to assess the conditions of the former UST and surrounding area, and a private utility locator was contracted to conduct a engineers I scientists I innovators