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I Introduction Roux Associates, Inc. (Roux) on behalf of Stuart Limited Partnership has prepared this Revised Data Gap Investigation Work Plan (Revised Work Plan) for the former Quality Cleaners Site in the Tracy Corners Shopping Center, located at 3081 North Tracy Boulevard in Tracy, California (Site, Figure 1). The investigation proposed herein has been designed to supplement previous investigations with the objective of adequately characterizing chlorinated volatile organic compounds (cVOCs), primarily tetrachloroethene (PCE) in the subsurface at the Site which is the result of a release associated with a former dry cleaner. Oversight of investigation and remedial activities are provided by the California Department of Toxic Substances Control (DTSC). This Work Plan has been prepared in response to a DTSC email dated March 18, 2022, in which additional investigation was requested. Roux and DTSC discussed the scope of work to be included herein during a virtual meeting that occurred on May 24, 2022. Following the virtual meeting, on June 3, 2022, DTSC issued a letter in which they provided comments to the results of soil vapor samples that were previously collected offsite along Scarlett Place. The offsite soil vapor results were summarized in a report entitled Off-Site Scarlet Place Soil Gas Sampling Results, Scarlett Place —Quality Cleaners, prepared by Partner Engineering and Science, Inc. (Partner), dated September 30, 2021. In their June 3rd letter it is noted that the DTSC does not concur with the recommendation that no further action offsite to the south is warranted and requested that stakeholders be notified, additional sampling be completed both of existing soil gas wells and sub-slab and indoor air sampling at residences in addition to additional delineation of the soil gas plume and determination of the soil vapor extraction (SVE) system southern radius of influence (ROI). Roux notes that a notice informing stakeholders of the sample results was posted to Envirostor on June 10, 2022. In response to DTSCs June 3rd letter, Roux submitted a Data Gap Investigation Work Plan (Work Plan) on July 28, 2022, for the collection of data to support a spatially and temporally comprehensive understating of current soil vapor conditions at the Site. On August 31, 2022, DTSC issued a memorandum requesting changes to the scope of work described in the Work Plan. The revised scope of work now includes soil vapor sampling at five additional soil vapor points, which will include two offsite residential locations, two sub-slab locations within the building located on the western portion of the site(supermarket building),and one location along the western property boundary. This is being proposed as the first step of a proposed iterative process to determine the potential risk of soil vapor intrusion at the adjacent residences and is consistent with the Draft February 2022 Supplemental Guidance: Screening and Evaluating Vapor Intrusion. Once the data from the sampling proposed herein is available, Roux will review and make recommendations on potential next steps for DTSC to review and approve. At this time, Roux cannot determine the SVE system ROI because the SVE system that previously operated at the Site has since been removed. Roux hereby proposes to collect the soil vapor samples proposed herein to determine if resumption of SVE operations is appropriate or an alternative remedial/mitigation approach may be warranted. Specifically, this Revised Work Plan focuses on additional investigation necessary to address data gaps associated with soil gas concentrations along the western and southern property boundaries, indoor air concentrations within the former dry cleaner building and supermarket building, and groundwater concentrations, specifically the vertical and lateral extent of groundwater impacts. The data gap investigation 3989.0001S101/R Revised Data Gap Investigation Work Plan I ROUX 11