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Additional Subsurface Investigation Work Plan 17 W Washington Street, Stockton, California Drilling and Sample Collection The proposed scope of work consists of advancing and logging three (3) soil borings (designated SB-1 to SB-3) to a depth of 15 feet below ground surface (bgs) at the locations shown on Figure 2 to collect groundwater and soil gas samples. As required, the selected drilling contractor, Environmental Control Associates of Aptos California, holds a California C-57 driller’s license. Each of the proposed soil borings will be advanced at the Site with a truck-mounted, direct push drilling rig to collect groundwater and soil gas samples. The borings will be advanced to a planned depth of 15 feet bgs or refusal, whichever is shallower. Soil core from each boring will be continuously collected in liners. Soils encountered will be logged using the Unified Soil Classification System. A photoionization detector (PID) will be used to screen soil cores in the field and the PID readings will be included on the boring logs. For groundwater collection, a temporary well will be constructed using well materials consisting of 1-inch diameter, 0.010 slotted, poly vinyl chloride (PVC) piping installed in the borehole to facilitate groundwater recovery. If groundwater is not encountered or is not readily available for sample collection, a soil sample will be collected (in place of a groundwater sample) from the boring and analyzed for the same parameters as listed below. Additionally, if field observations indicate soil contamination may be present, AEI will collect additional soil samples to be placed on hold. Soil Vapor Sampling Following groundwater sample collection, soil vapor probes will be installed in the three soil boings. Each soil boring will be completed as a temporary, dual-level soil gas well for the collection of soil gas samples, with probes at approximately 5 and 15 feet bgs. Sampling of soil gas will be conducted in accordance with the Advisory, Active Soil Gas Investigations by the California Department of Toxic Substances Control (DTSC), et al (2015), including vacuum testing and purging the probes and by using a helium shroud during sampling. The soil gas samples will be collected through a calibrated flow controller and into one-liter laboratory supplied evacuated canisters. Boring Destruction Following completion of sample collection and removal of tooling, the borings will be backfilled with neat cement grout in accordance with the permitting agency requirements. Investigation Derived Waste Investigation derived waste will be left onsite in drums. Disposal will depend upon the receipt of the analytical results and upon client approval. Laboratory Analysis Samples collected will be transferred under appropriate chain-of-custody documentation to a state-certified laboratory for analysis. Laboratory analysis of groundwater (or soil) samples collected will consist of the following: x VOC using U.S. Environmental Protection Agency (EPA) Testing Method 8260.