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Geosyntec <br /> consultants <br /> Soil vapor sampling results will be compared to the San Francisco Bay Regional Water Quality <br /> Control Board's ESLs for residential soil vapor (RWQCB, 2019). The ESLs for 1,2,3-TCP, 1,2- <br /> DCP, DBCP, and chloroform in soil vapor and the laboratory-provided reporting limits are <br /> provided in Table 1. The objective will be to interpret soil gas results to determine if an exceedance <br /> of residential screening levels is present on-Site, including at a location where groundwater 1,2- <br /> DCP and 1,2,3-TCP concentrations are the highest. Based on this interpretation, one of two <br /> outcomes will ensue: <br /> 1. If on-Site soil gas sampling results indicate no exceedances above residential screening <br /> levels, then off-Site soil gas assessment is not warranted; or <br /> 2. If on-Site soil gas sampling results indicate one or more exceedances above residential <br /> screening levels, then Site-specific correlation factors developed from on-Site results <br /> will be applied to groundwater concentration results from off-Site wells, to determine <br /> if additional off-Site soil gas assessment is warranted. <br /> Site-specific correlation factors will be developed for 1,2-DCP, 1,2,3-TCP,DBCP and chloroform <br /> by evaluating the soil vapor and groundwater sample results. These correlation factors can then be <br /> applied to off-Site locations, to aid in evaluating potential vapor intrusion risk to residents based <br /> on groundwater COC concentrations in samples collected from off-Site monitoring wells MW-26, <br /> MW-27, MW-28 and MW-30. These four off-Site wells are planned to be sampled as part of the <br /> Q3-2021 groundwater monitoring event. Based on the results of this investigation and the Q3- <br /> 2021 groundwater monitoring event, the vapor intrusion risk for off-Site areas will be evaluated. <br /> Off-Site soil vapor sampling may be proposed, depending on the results of this investigation. <br /> Using the data collected from this investigation, the Threshold Concentrations will be reviewed, <br /> and, if warranted, the Threshold Concentrations for 1,2-DCP, 1,2,3-TCP, DBCP, and chloroform <br /> may be revised. <br /> Work Plan for Vapor Intrusion Investigation 5 July 30,2021 <br />