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23 May 2023 Project No. 14-3154 Page 6 of 7 5.0. CONCLUSIONS AdvancedGeo An Employee- Owned Company Based upon the environmental activities completed, AGI provides the following conclusions: Buried waste, a glass waste cell, or disposal area was not identified in the Trench T29 area. • Pieces of trace glass cullet were observed at 1 and 3 feet bsg in T29134 and between 3 and 4 feet bsg in the remaining borings, except for borings T29B6 and T29131 5. AGI does not consider the pieces of trace glass cullet to be waste glass. The glass comprising the waste cells and disposal areas identified to the south and west (17100 and 17200 Murphy Parkway) of the site is inconsistent with the glass pieces observed during this investigation. The pieces of trace glass cullet observed during this investigation were more consistent with surficial glass encountered at the property that was historically gathered and stored on concrete pads north of the railway pending recycling. • Only pieces of trace glass cullet were encountered at shallow depths in the T29 area during the investigation. The waste pits encountered to the south of the railway, and since remediated, contained large shards of broken glass. The pieces of trace glass cullet encountered in the T29 area were entirely different. • Total PCB concentrations detected in the soil samples were below the ESL, DTSC- SL, and RSL for total PCBs in shallow soil at commercial/industrial properties. Additionally, total PCB concentrations were below the ESL for leaching to groundwater levels (Table 1). • SVOC and PAH concentrations detected in the soil samples were below their respective ESLs, DTSC-SLs, and RSLs for shallow soil exposure at commercial/industrial properties. Additionally, SVOC and PAH concentrations were below their respective ESLs for leaching to groundwater levels (Table 2). • Except for arsenic, Title 22 metal concentrations detected in the soil samples were below their respective ESLs, DTSC-SLs, and RSLs for shallow soil exposure at commercial/industrial properties (Table 2). • Arsenic was the only Title 22 metal detected above environmental screening levels in the soil samples analyzed; environmental screening levels for arsenic range from 0.31 mg/kg (ESL) to 3.0 mg/kg (RSL). Arsenic was detected at concentrations ranging from 1.1 mg/kg (T291310) to 8.9 mg/kg (T29B3). The average arsenic concentration was 2.1 mg/kg. Soil analyzed from T29133 was the only sample to exceed the RSL of 3.0 mg/kg. Arsenic has historically been detected in shallow soil samples collected from the site. Previous investigations have established a site-specific background concentration of 8.6 mg/kg for arsenic (Site Assessment Summary Report — Final dated 21 June 2018). Additionally, the DTSC has determined that background concentrations of arsenic in California soils are commonly high, ranging anywhere from 0.6 mg/kg to 11 mg/kg -Background