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SUPPLEMENTAL SITE INVESTIGATION WORK PLAN South Pointe Property Stockton, California Site Background • The site is in an area of Stockton with extensive historical industrial use including bulk fuel plant operations, chemical and materials warehouses, railroad tracks, petroleum storage, and gas and oil pumps. Various petroleum companies owned, operated and/or leased properties in the immediate vicinity of the site from approximately 1917 until 1982 and petroleum hydrocarbon leaks and spills were documented during this time. Soil, groundwater, and soil vapor beneath adjacent and nearby sites have been impacted by a variety of chemicals including gasoline, diesel, heavy metals, SVOCs, and VOCs. Regional impacts from former surrounding industrial properties including bulk fuel plant operations are considered to represent a REC and PVEC. The Phase I ESA also identified the McCormick & Baxter Superfund site approximately 2,000 feet west of the site across Mormon Slough and chemical impacts identified in sediments within the Stockton Channel north of the site as RECs associated with off-site chemical releases with the potential to affect groundwater quality beneath the site. 2.2.4 Phase II ESA - 2021 Stantec completed a Phase II ESA of the Property in 2021 (Stantec, 2021). The Phase II ESA was focused on addressing two key data gaps by conducting a focused soil assessment to delineate the vertical extent of OCPs and lead in several areas of the Site, and a soil vapor investigation to assess the presence of VOCs in soil vapor at concentrations potentially requiring remediation and/or mitigation as part of future redevelopment plans. The scope of work for the Phase 11 ESA included: 1. Excavation of test pits at 20 locations for collection of soil samples from subsurface fill materials and underlying native soil; 2. Completion of a site-wide "passive" soil vapor survey utilizing sorbent vapor sampling modules at 39 locations across the site, corresponding to the nodes of an approximate 100-foot by 100-foot sampling grid, with subsequent laboratory analysis for VOCs; and 3. Completion of active soil vapor sampling at five locations selected based on the results of the passive soil vapor survey,with collection of soil vapor samples from depths of 5 and 10 ft bgs at each location and subsequent analysis of samples for VOCs. The results for the soil investigation and passive/active soil vapor survey are presented below. Chemical data tables and summary figures from the 2021 investigation are attached as Appendix B. Soil Conditions Previous site assessment completed in 2007 identified concentrations of OCPs and lead in shallow soils at concentrations exceeding risk-based screening criteria for residential and commercial use. 2.5