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SUPPLEMENTAL SITE INVESTIGATION WORK PLAN South Pointe Property Stockton, California Scope of Work SCOPE OF WORK The scope of work detailed herein is intended to provide additional soil chemical data to delineate chemicals of concern in soil and groundwater beneath the site. The proposed work scope includes characterization of the 3,000-yard stockpile present in the central portion of the property as well as underlying fill and native materials and is designed to augment soil data collected between 2007 and 2021. Soil samples will be retained from appropriate depths and analyzed for site-related COCs. As requested previously by DTSC, several boreholes will be extended to first-encountered groundwater for collection of grab groundwater samples to determine if underlying groundwater has been impacted by site-related CDCs. 4.1 INVESTIGATIVE APPROACH Forty (40) boreholes will be advanced to a maximum anticipated depth of 9 feet below street grade, which is the approximate vertical extent of previously-detected soil impacts. Borehole locations have been selected to complement historical data, and to provide broad coverage across the site. To maximize coverage, Stantec created a 150 ft by 75 ft grid overlay to facilitate adequate spacing of boreholes. Borehole locations are illustrated on Figure 7, and the sampling strategy is described below. 4.1.1 Soil Assessment - Boreholes 1 through 18 will penetrate the 3,000 cy soil pile, which extends between 0.5 and 3.5 feet above street grade; therefore, these boreholes will extend to a maximum depth of 12.5 ft bgs, equating to a depth of 9 feet below street grade. At these locations, one to two representative samples will be collected from the soil pile, and up to three soil samples will be collected from underlying native and/or fill materials. The sample scope is summarized on Table 1. - Boreholes 19 through 40, which do not penetrate the soil pile, will extend to 9 ft bgs.Three soil samples will be collected from each borehole (ground surface, 4 ft bgs, and 9 ft bgs). The sample scope is summarized on Table 2. The deepest sample from each borehole will be held by the analytical laboratory pending analysis of the shallower samples and will be analyzed only if the overlying sample contains COCs at concentrations exceeding screening levels. Samples will be analyzed for the primary site-related CDCs, identified as those that have been detected previously at concentrations exceeding risk-based screening levels for unrestricted site use: metals as lead, cobalt, and mercury, and OCPs. Additional constituents that have been detected previously at the site at much lower frequency than the primary COCs are polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and polychlorinated biphenyls (PCBs). A subset of samples (corresponding 4.1