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Shed 7 UST Closure in Place Work Plan September 6, 2024 Page 2 geophysical survey. Using a metal detector, the utility locator delineated an approximately 9-foot by 15-foot area suspected to be the partial extent of the UST. The existing building and adjacent platform prevented a full delineation of the UST extent during the geophysical survey. 1.2 Rationale for Closure in Place The Port is requesting CIP of the former UST to minimize impact to its existing infrastructure in the vicinity of Shed 7. In addition, the CIP would facilitate timely completion of utility and building foundation repairs that are being completed for a tenant at the property. The UST is located within approximately 1 foot from the existing foundation for Shed 7. Based on the available information, the tank extends under the raised platform and may extend under the building foundation. In addition, subsurface utilities are believed to be located directly above and adjacent to the UST (Figure 2). Complete removal of the UST would require a deep excavation (estimated at 12 feet below ground surface [bgs]) and would significantly increase the time and effort for completing the utility and building foundation repairs at Shed 7. 2. FIELD ACTIVITIES Angled soil borings will be extended under the former UST to facilitate collection of soil and groundwater samples. The following paragraphs describe the planned field activities in support of CIP for the former UST. 2.1 Utility Clearance Locations for proposed borings will be marked with white paint. Underground Service Alert of Northern California will be contacted a minimum of two working days prior to commencement of drilling. Additionally, a private utility locator will be on-site to clear the planned drilling locations of potential utilities, pipelines, and/or other subsurface obstructions. Drilling locations may be adjusted if the planned boring locations cannot be reliably cleared by the private utility locator. Alternative locations will be reviewed with the SJCEHD inspector prior to drilling. 2.2 Sampling and Laboratory Analysis Prior to drilling, Geosyntec will obtain a subsurface drilling permit from SJCEHD. Two angled soil borings will be advanced by a California C-57 licensed driller utilizing a sonic drill rig under the direct oversight of Geosyntec personnel and SJCEHD staff. Proposed boring locations target native soil underneath the UST at each end of the tank and are displayed in Figure 3. The total depth of the UST is approximately 10 feet bgs and the borings will extend to the groundwater table, which is expected to occur between 10-15 feet bgs. At each boring, soil cores will be collected in polyvinyl chloride (PVC) liners from the ground surface until the target depth. The PVC liners will be cut, and soil samples will be collected at the following target depths: • Southern boring at approximately 1 foot bgs (below fill pipeline), 10 feet bgs (near UST bottom), and 15 feet bgs(soil/groundwater interface) engineers I scientists I innovators