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Soil Gas Sampling Workplan 601 North Central Avenue Tracy, California 95376 Partner Project No. ES22-353833 October 2, 2025 • Notify underground service alert north a minimum of three business days prior to drilling activities to clear public utilities; • Clear boreholes of utility lines through a geophysical survey. Boring placement will be modified as necessary based on the geophysical survey results to avoid damaging underground features.Additionally,to the extent practical based on subsurface lithology, clear boring locations using hand tools; • Subcontract with a State-licensed (C-57) drilling contractor to advance a total of five borings at the Site to a terminal depth of 15.5 feet bgs; • Continuously field-screen each soil boring using a photoionization detector (PID); • Install a temporary soil gas probe in each boring at 5 and 15 feet bgs (two soil gas probes per boring). Temporary soil gas probes will be constructed within the direct-push borings upon completion of drilling to the proposed terminal depth. A new section of /a-inch diameter Nylaflow tubing with a new 1/4-inch diameter porous filter at the terminal end will be inserted into the borehole to the desired sampling depth. One-inch diameter polyvinyl chloride (PVC) casing will be used as a guide for the tubing to ensure that the desired sampling depth will be achieved. Sand will be poured into the boring annulus to form an approximately 1-foot long sand pack around the filter tip, at which time the PVC piping will be withdrawn. Approximately 1 foot of dry, granular bentonite will be placed atop the sand pack and the remainder of the borehole will be backfilled with hydrated bentonite to the next desired sampling depth where a soil gas probe will be similarly constructed. Upon installation of the shallowest probe, the remainder of the borehole will be backfilled with hydrated bentonite to the ground surface to form a seal. The sampling end of the tubing will be fitted with a valve and the probe will be labeled for identification. To allow subsurface conditions to equilibrate, no further procedures will be performed for approximately two hours. Soil gas sampling will not be conducted during or immediately after any significant rain event (e.g., 1/2 inch or greater) or any onsite watering which may cause no- flow or low-flow conditions. Details of the soil gas probe construction are provided in Figure 2; • Purge each probe, then collect and prepare up to 10 soil gas samples for laboratory analysis using laboratory-provided, batch-certified SUMMA canisters and flow controllers with a 5- to 10-minute sample period; 2 Page PARTNER 0 00