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California Regional Water Quality Control Board -Central Valley Region 3 October 2023 Page 2 or olfactory observations of soil contamination were noted in any of the soil borings (Attachment A).At each of the 25 locations, the soil vapor probes are constructed with %-inch polyethylene tubing within a single borehole, with probe depths at approximately 5, 10, and 15 feet below ground surface (bgs).At SV-103 and SV-110, two deeper nested probes at approximately 20 and 25 feet bgs were constructed next to the nest probes at 5, 10, and 15 feet bgs. Soil vapor probe details are provided in Table 1 and locations are provided in Figure 2. In accordance with the Advisory-Active Soil Gas Investigations (California Environmental Protection Agency, 2015), soil vapor probes will be decommissioned in the following manner: • At each location, surface completion materials will be excavated to a depth of approximately 3 feet bgs, removing the cement grout and protective well boxes. • If possible,the exposed tubing will be removed by hand. If tubing cannot be physically removed from the borehole,tubing will be cut near the bottom of the excavation. • For any tubing left in-place, neat cement grout will be injected into the exposed tubing using a syringe or peristaltic pump until the tubing is filled. • The excavated hole will be filled with neat cement grout. • Each location will be restored to closely match its original surface conditions per City of Ripon requirements (i.e., asphalt pavement, concrete, and/or paving stones). Haley&Aldrich will subcontract with a California-licensed drilling company to support the decommissioning activities described above. WASTE MANAGEMENT Soil and debris generated during the decommissioning efforts will be containerized in labeled, 55-gallon drums, temporarily stored at secure location pending waste profiling and disposal at an appropriate waste disposal facility. Schedule and Reporting Field activities will be tentatively scheduled for the fourth quarter of 2023, pending concurrence with this Work Plan, permitting time frames for local agencies and subcontractor availability. Upon completion of decommissioning activities, Haley&Aldrich will prepare a report documenting the methods and any substantive deviations from this Work Plan. RICH