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Shed 7 UST Closure in Place Work Plan September 6, 2024 Page 3 • Northern boring at approximately 10 feet bgs (near UST bottom) and 15 feet bgs (soil/groundwater interface) Soil sample depths will be adjusted in the field, as appropriate,to align with field observations and in consultation with the SJCEHD inspector. Soil collected during drilling activities will be field screened for volatile organic compounds (VOCs) using a photoionization detector and logged for lithology under the direction of a California Professional Geologist in general accordance with the Unified Soil Classification System (USCS). The USCS information will be recorded, along with other notable sample features. Field observations of staining, odors, or other soil characteristics will be noted on soil boring logs. Historical groundwater levels from monitoring wells in the greater Port of Stockton area suggest groundwater levels near Shed 7 to be encountered within approximately 5 feet of the UST bottom (i.e., 10-15 feet bgs). Given the expected depth of groundwater, one grab groundwater sample will be collected at each soil boring. During borehole advancement, a slotted PVC casing will be inserted through the inner drill casing, and once the target sample depth is reached,the outer casing will be retracted to expose the screen to groundwater. Following collection, soil and groundwater samples will be labeled with project identification, sample location, sample depth, and time and date of sampling and placed in an ice-filled cooler for transportation under chain-of-custody procedures to a State of California-certified laboratory for the following analyses: • Gasoline range organics by Unites States Environmental Protection Agency(USEPA) Method 8015B • Diesel range organics by USEPA Method 8015B • Benzene, toluene, ethylbenzene, and xylenes (BTEX) by USEPA Method 8260B • VOCs by USEPA Method 8260B • Lead by USEPA Method 7421 Analytes were determined based on SJCEDH's recommended minimum verification analyses for USTs containing heating oil. Due to the limited documentation regarding the UST, the planned analyses were expanded to include SJCEDH's recommended analytes for USTs containing unknown fuel. Reporting limits and method detection limits are presented in Table 1. Following sampling, each borehole will be tremie grouted to the surface with neat cement grout (Portland Type I/II or equivalent). engineers I scientists I innovators