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Chevron Emmermentel Management Company - 2 - 8November 2021 <br /> probes at concentrations of 760 uglm' in SV-], 6,200 ugW in SV-8, and 440 ug/m3 in <br /> SV-9. Oxygen concentrations in each probe were 5.7% in SV-T, 1.2% in SVA, and <br /> 1 .3% in SV-9. The LTCP threshold for bicattenuabon requires oxygen concentrations <br /> be greater Man 4% therefore, SV-T has a bioattenuagon zone but SVA and SV-9 do <br /> noL The concentration of benzene at SV-] was less than the LTCP commercial <br /> screening value (with bicadenuation) of 280,000 ug/ma. The concentrations of benzene <br /> at SVA and SV-9 exceeded the LTCP commercial screening value (without <br /> bioattenuation) of 280 ug/m3. <br /> Ansel conduces Mat the concentration of benzene in soil vapor at SV-] does not <br /> coed the LTCP rumme vial screening value Indicating that concentrations below Me <br /> rent marine repair shop sanctum are not currently a vapor intrusion risk to occupants <br /> of the structure. Arcadis also concludes that benzene at SVA and SV-9 exceed the <br /> LTCP commercial screening value (without bicattenualion) for potential vapor intrusion <br /> but that there is currently no complete vapor intrusion pathway given they are located <br /> witllin the Site's parking lot, and there are an manding structures at that location. <br /> Arcadis will reassess the path 0 closure for the Site and will provide an action plan <br /> within 45 days of Central Valley Water Board response to the SV Sampling Report. <br /> Central Valley Water Board staff concurs with the proposal to submit an action plan that <br /> assesses a path to closure. Therefore, please submit the proposed action plan by <br /> 31 December 2021. We are also available to meet with Arcadis and CEMC to discuss <br /> that path to closure prior to submittal of the proposed action plan. <br /> Feel free to contact me with any questions or concerre regarding this letter at <br /> (916) 4f;44622 or SIl Bratian(utwaterboardscag . <br /> William Bushed, P.E. <br /> Water Resource Contra Engineer <br /> Private Sites Cleanup Unit <br /> Knelt Shelton, P.E. w <br /> Senior Water Resource Control Engineer <br /> Private Sites Cleanup Unit ® .,. <br /> cc. Michael Mailloux, Chevron Environmental Management Company, San Raman <br /> Auction Lehman, Arcadis U.S., Inc., Concord <br />