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SUPPLEMENTAL SITE INVESTIGATION WORK PLAN South Pointe Property Stockton, California Site Background Soil and groundwater chemical data were compared to various risk-based screening criteria, and groundwater chemical data were compared to several sets of then-current screening criteria for both residential and commercial exposure scenarios Laboratory results revealed elevated concentrations of OCPs, lead, petroleum hydrocarbons, and PAHs in site soils at concentrations exceeding one or more screening levels. Elevated concentrations of OCPs and lead were primarily limited to the western and central portions of the site. Elevated concentrations of petroleum hydrocarbons and PAHs were identified in the northeast portion of the site, overlapping with the adjacent Promenade property. OCP impacts were generally aligned with the historical rail spur and the source was believed to have been the result of previous site industrial activities associated with loading/unloading of agricultural materials along the rail spur, as well as possible application of pesticides for weed control along the spur and around areas of grain milling and storage. The distribution of elevated concentrations of OCPs and lead in shallow soils was observed to be non-uniform, with elevated concentrations generally observed at various depths between ground surface and 5 ft bgs. WKA attributed this condition to mixing of surface soils with building demolition debris during previous building demolition and site grading activities. This is supported by field observations whereby unconsolidated building debris was found to be mixed with apparently native soils in the upper 5 ft bgs across the site. Several areas were identified where OCPs and/or lead extend deeper than 5 ft bgs, and as deep as 9 ft bgs. Based on these data, WKA developed a conceptual remediation plan for the site, which is illustrated on WKA Figure 7, included in Appendix A. This figure illustrates portions of the site (and the adjacent Promenade property) where constituents of concern (CDCs) in soil exceeded then-current risk-based screening criteria. 2.2.3 Phase I ESA - 2020 To better understand the site history and any new potential environmental concerns, Stantec completed a Phase I environmental site assessment (ESA) dated May 4, 2020 (Stantec, 2020). Stantec identified the following recognized environmental conditions (RECs). • Long-term industrial use of the site has resulted in documented chemical impacts to soil and/or groundwater. Based on previous environmental assessments, documented chemical impacts are attributable to multiple operational sources that have since been removed. Two general areas of impacts to underlying soil have been identified: petroleum hydrocarbon-affected soil identified near the northeastern portion of the site, and heavy metal and/or dieldrin-affected soil identified near remnants of the previous railroad tracks between former agricultural supply warehouses and the far western end of the site. Groundwater beneath the site is impacted by petroleum hydrocarbons originating from multiple documented off-site, upgradient sources. These documented soil and groundwater conditions represent a REC and potential vapor encroachment condition (PVEC). 2.4