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Dopaco Inc. Area Case #3 - 2 - 7 December 2021 <br /> <br /> <br /> <br />historical soil concentrations represent an impediment to closure. Central Valley <br />Water Board staff concurs. <br /> <br />3. In the Report, AECOM notes historical soil gas samples which contained <br />benzene above LTCP Petroleum Vapor Intrusion to Indoor Air Media-Specific <br />commercial thresholds. AECOM also notes that these samples were collected <br />prior to removal of 300 cubic yards of impacted soil in the vicinity, and thus do <br />not represent current conditions. AECOM identifies this as a remaining data gap. <br />Central Valley Water Board staff concurs with evaluating the vapor intrusion risk <br />for future construction in the area of the former USTs. <br /> <br />4. In the Report, AECOM states that existing shallow soil data is insufficient to <br />properly evaluate Site conditions against LTCP Direct Contact and Outdoor Air <br />Exposure Media-Specific criteria, and thus a related data gap remains. Central <br />Valley Water Board staff concurs. <br /> <br />Based on the above comments, Central Valley Water Board staff requests the following: <br /> <br /> By 11 February 2022, please submit a work plan: <br /> <br />o Please include a proposal for shallow soil sampling to satisfy both LTCP <br />Petroleum Vapor Intrusion to Indoor Air and Direct Contact and Outdoor Air <br />Exposure Media-Specific criteria. The proposal should include the <br />collection of soil samples between both 0-5 and 5-10 feet below ground <br />surface, with analysis to include at least TPHg, TPHd, benzene, toluene, <br />ethylbenzene, total xylenes (collectively BTEX), and naphthalene. <br /> <br />o Please include a proposal to install and sample soil gas wells at the Site to <br />satisfy LTCP Petroleum Vapor Intrusion to Indoor Air Media-Specific <br />criteria. Proposed well construction and sampling should be in accordance <br />with the Department of Toxic Substances Control (DTSC) joint-agency <br />2015 guidance document Advisory – Active Soil Gas Investigations. <br />Proposed soil gas sample analysis should include at least TPHg, TPHd, <br />BTEX, naphthalene, oxygen, and the selected leak detection compound. <br />For quality assurance purposes, the proposal should include quantification <br />of leak detection compound under the sampling shroud for comparison to <br />the concentration in the corresponding sample. <br /> <br /> By 1 May 2022, please sample Site wells and submit a groundwater monitoring <br />report. Please include TPHd in the sample analytical suite. <br /> <br /> <br />If you have any questions or concerns regarding comments in this letter or regarding the <br />Site, please contact Alan Buehler at (916) 464-4615 or by email at <br />alan.buehler@waterboards.ca.gov.