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Sampling and Analysis Plan for Phase II Environmental Site Assessment South Pointe Property: 701, 705, 833, 855 West Weber Avenue Stockton, California Sampling Design and Rationale May 17, 2021 Table 4-1 Soil Sampling Design and Rationale Sampling Depth' Analytical Location/ID Rationale Number (feet) Parameters TP-1 through TP-20 2/5/ 10 OCPs by EPA Method 8081; Vertical delineation of OCPs and lead in lead by EPA Method 6010 soil -fill at 2', native at 5', native at 10' 1 —Target depths may vary based on field observations and presence of fill materials.See text for discussion. 4.2 SOIL VAPOR SAMPLING The site has not been assessed for the presence of VOCs in subsurface soil vapor. The site and surrounding area have been used for industrial activities since the 1890s and use of adjacent sites has included the storage and distribution of bulk petroleum hydrocarbon products. Extensive groundwater impacts in the area have been documented. Additionally, review of historical data suggests that the site has not been assessed for sources of VOCs connected to historical use (such as rail alignments, drainage sumps, chemical storage areas, and incidental releases due to use of solvents, fuel products, etc.). If present, VOCs in soil vapor beneath the site may readily migrate vertically into occupied spaces, a process known as vapor intrusion. This condition would pose a potential threat to the health of future site occupants and/or residents. Therefore, assessment of potential vapor intrusion concerns is critical for planning and executing redevelopment plans for the site. Stantec proposes assessing soil vapor conditions using two methods: passive and active sampling. Passive sampling consists of installing sorbent sampling modules (produced by Beacon Environmental Services Inc. [Beacon])within the subsurface at 40 locations across the site, corresponding to intersecting nodes of a 100' by 100' sampling grid. The proposed sampling grid and passive soil vapor sampling locations are illustrated on Figure 3. The sorbent sampling modules, installed at a depth of approximately 2.5 feet below grade, are left in place for approximately two weeks to allow VOCs present in soil vapor to sorb to the sample media. The modules are then retrieved and analyzed for VOCs by EPA Method 8260C. VOCs are reported on a mass basis (for example, 100 micrograms of benzene) rather than on a concentration basis. This approach allows identification of areas of the site with relatively elevated mass accumulations of VOCs which can then be quantified by active sampling using traditional methods (i.e., collecting soil vapor samples in Summa canisters for analysis of VOCs by EPA Method TO- 15). Based on results of the passive soil vapor survey Stantec anticipates installing multi-depth soil vapor probes at up to ten locations across the site. At each location, soil vapor probes will be installed at anticipated depths of 5 and 12 feet below grade, to allow assessment of VOCs present in soil vapor and to assess potential sources (i.e., whether VOCs may be sourced from shallow near-surface sources or from underlying impacted groundwater) and to evaluate vertical attenuation of VOC concentrations. The proposed soil vapor sampling schedule is summarized in Table 4-4. M Project No.: 185704833.5.3&5.4 4.2