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3 Scope of Work <br /> 3.1 Sampling Rationale <br /> While a significant amount of investigative and remedial activities have been completed at the Site, in a <br /> March 18, 2022 email and August 31, 2022 memorandum the DTSC noted the following actions need to be <br /> completed: <br /> • Offsite soil gas sampling to further characterize soil vapor concentrations in residential areas <br /> to the west and south of the Site; <br /> • Soil vapor sampling along the onsite sewer line to further characterize onsite soil vapor <br /> concentrations, establish a concentration gradient, and determine if additional step-out <br /> sampling locations to the west will be necessary; <br /> • Completion of sub-slab soil gas characterization within the supermarket building; <br /> • Indoor and outdoor air sampling within the former dry cleaner and supermarket buildings; and <br /> • Further characterization of groundwater conditions. <br /> This Revised Work Plan outlines a sampling plan to address the data gaps listed above. Roux proposes the <br /> collection of data to support a spatially and temporally comprehensive understating of current soil vapor and <br /> groundwater conditions at the Site and adjacent residential areas to the west and south, along with the <br /> requested indoor air data. A spatially and temporally comprehensive understanding of subsurface conditions <br /> will then be used to supplement the conceptual site model for the Site so that additional data gaps can be <br /> identified and assessed and/or remedial actions can be effectively evaluated and implemented. This <br /> sampling program includes the collection of soil gas, indoor/outdoor air, and groundwater samples, for <br /> analysis of VOCs. The scope of work includes the installation and sampling of two soil vapor probes on the <br /> residential properties located south of the Site, two soil vapor probes west of the Site on Peach Street, one <br /> on-site soil vapor probe location along the western property boundary, two sub-slab soil vapor pins in the <br /> supermarket building, and two temporary groundwater wells. Indoor and outdoor air samples will also be <br /> collected from the former dry cleaner and supermarket buildings. <br /> Additional details regarding the sampling strategy are provided in the sections that follow. Details regarding <br /> the field preparation, field sampling, procedures, and analytical methods planned for the field investigation <br /> activities are provided in Section 4.0 of this Work Plan. <br /> 3.2 Proposed Sampling <br /> This section describes the samples to be collected from each media during the investigation, including the <br /> number, type, location, and depth the samples. <br /> 3.2.1 Groundwater Sampling <br /> A total of eleven (11) groundwater samples will be collected from existing monitoring wells MW-1 through <br /> MW-5 (Figure 2) as well as two proposed nested temporary well locations (TW-1 S/D and TW-2S/D), a field <br /> duplicate sample, and a field blank sample. In an effort to establish vertical delineation of Site COCs in <br /> groundwater, two depth intervals will be sampled at each temporary well location: one in first groundwater at <br /> approximately 10 ft bgs and a second within the first encountered water-bearing zone below this depth. <br /> Groundwater samples will be submitted to a certified laboratory under chain-of-custody procedures and <br /> 3989.0001S10VR Revised Data Gap Investigation Work Plan I ROUX 16 <br />