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Reynolds & Brown - 2 - 21 November 2023 <br />The sample collected from boring T29B3 contained a concentration of total PCBs <br />greater than the environmental screening level (ESLs) for a residential setting. <br />However, total PCB concentrations detected in all soil samples were below the ESLs for <br />commercial/industrial shallow soil exposure and leaching to groundwater. The sample <br />collected from boring T29B7 contained a benzo(a)pyrene concentration greater than the <br />ESL for a residential setting. However, SVOCs and PAH concentrations detected in all <br />soil samples were also below their respective ESLs for commercial/industrial shallow <br />soil exposure and leaching to groundwater. Except for arsenic, all Title 22 metal <br />concentrations detected in the soil samples were below respective ESLs for residential <br />shallow soil exposure. Concentrations of arsenic detected at the Site ranged from 1.1 to <br />8.9 milligrams per kilogram (mg/kg), exceeding the commercial/industrial shallow soil <br />exposure ESL. However, these concentrations are less than the typical maximum <br />background concentrations observed in the region and the previously established site- <br />specific background concentration of 8.6 mg/kg. <br />AGI concludes that no buried waste, glass waste cell, or disposal area was identified in <br />the Trench T29 area. The pieces of trace glass cullet observed during the investigation <br />were consistent with surficial glass previously encountered at the Site that was <br />historically gathered and stored pending recycling. Based on the results of the <br />investigation presented in the report, AGI recommends the glass waste disposal <br />investigation at the Site be considered for closure. <br />COMMENTS <br />Based on boring data presented in the Report, Central Valley Water Board staff concur <br />that no buried waste or glass disposal areas were identified, and the absence of <br />pollution has been verified for the T29 area. Prior to winding down regulatory oversight <br />for the Site property under the Central Valley Water Board Site Cleanup Program, a <br />land use covenant (deed restriction) should be prepared in consultation with Central <br />Valley Water Board staff that requires implementation of the 12 July 2019 Soil <br />Management Plan created for the Site and specifies commercial uses for the Site. On- <br />going regulatory requirements for the Site property as a solid waste site will also <br />continue under the San Joaquin County Environmental Health Department Local <br />Enforcement Agency. <br />If you have any questions or concerns regarding this letter, please contact Nathan <br />Casebeer at (916) 464-4665 or by email at nathan.casebeer@waterboards.ca.gov. <br />NATHAN CASEBEER, P.G. <br />Senior Engineering Geologist <br />Federal/Private Site Cleanup Unit