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W <br /> Water Boards V •,• •- ^•^^•A. <br /> Central Valley Regional Water Quality Control Board <br /> 6 Apr M22 <br /> Chevron Environmental Management Company <br /> do Siodam Prilchar <br /> Arcadis U.S., Inc. <br /> 630 PIffia Drive, Suite 200 <br /> Highlands Ranch, CO 80129 <br /> REVIEW OF SOIL VAPOR ASSESSMENT WORK PLAN, 401 NORM SAN JOSE <br /> STREET, STOCKTON, SAN JOAQUIN COUNTY <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Boar) staff <br /> weu the 28 March 2022 Soil VaporThe essmant Work Plan (Work Plan) prepared <br /> by Amadis, U.S. Inc. (Arcadis) on behalf of Chevron Environmental Management <br /> Company (CEMC) for 401 North San Jose Street in Stockton (Site). CEMC submitted <br /> Me Work Plan pursuant to a 3 February 2022 discussion with Central Valley Water <br /> Board staff regal the previously proposed plan for additional emaciation that was <br /> concurred with in our 6 January 2022 letter. The purpose of the additional soil vapor <br /> assessment (which will also include sell and groundwater sampling, and a pump lest) is <br /> to provide information for determining what additional commutation is needed to reduce <br /> soil vapor concentrations below applicable screening levels. <br /> Arcadis proposes to advance 11 soil borings SV-10 through SV-20 to a depth of 25 feet <br /> below ground surface (hiss) for collection asoil, groundwater, and soil vapor samples at <br /> Me locations on Figure 4 of the Work Plan. Aradis will tolled sell samples at depths of <br /> 5. 101 15, 20, and 25 feet bgs. In addition, Arcadis will collect a grab groundwater <br /> ample from each boring. Aroadis will then coned each boring to a dual-nested s6I <br /> vapor Probe; wiled soil vapor samples at 3.5 feet and 7.5 feet bgs; and analyze the <br /> samples for oxygen, carbon dioxide, mellome, and helium. Arcadia will submit Me soil, <br /> groundwater, and soil vapor samples for laboratory andhols of applicable petroleum <br /> constituents. Soil vapor sampling will include tracer leak testing using helium wierin an <br /> enclosure placed over the sampling lmin and the soil vapor samples will be collected in <br /> 14iler Summa canisters. Arcadis will sample the wil vapor probes a minimum of <br /> 48 boom after installation. <br /> Arcadis also proposes to conduct a groundwater pump test using existing groundwater <br /> maintaining will M W-] to provide an estimate of water produchan and help guide an <br /> appropriate remedial approach follaMng the assessment. Aroadls selected MW-] for <br /> Me pump lest because the well has a 4-inch diameter casing and because monitoring <br /> well Mal in the plume area was destroyed prim to the soil excavation. An acis will <br /> lw <br />