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Former San Joaquin Cogeneration - 3 - 17 December 2020 Lathrop, San Joaquin County potential evaluation using the Waste Extraction Test using deionized water (DI WET) method and found low leaching potential of 0.0042 milligrams per liter (mg/L). • Arsenic was detected in soil samples and waste samples at a maximum concentration of 13.5 mg/kg, exceeding the commercial ESL of 0.32 mg/kg. • Hexavalent chromium was detected in several groundwater samples at concentrations ranging from 0.93 micrograms per liter (ug/L) 8.4 ug/L. Although there is currently no drinking water Maximum Contaminant Level (MCL) for hexavalent chromium, the detections are below the previously proposed MCL of 10 ug/L. • Arsenic, selenium, ammonia, nitrate as nitrogen, and nitrate as nitrate collected was detected at concentrations exceeding screening levels in one or more grab groundwater samples. • A maximum concentration of 2,590 mg/L of total dissolved solids (TDS) in boring B1 exceeds the MCL of 500 mg/L. Additional Site Assessment Summary Between 22 and 25 June 2020, AGI conducted additional site assessment activities at the Site including advancing 36 soil borings (B44 through B79) to depths ranging from two feet bgs to 20 feet bgs, collecting soil samples from multiple depths for analysis, and collecting grab groundwater samples from five of the borings for analysis. The objective of the additional assessment activities was to define the lateral and vertical extent of the PCB- and TPH-impacted soil and waste material beneath the South Waste Cell, which extends into the eastern portion of the Site, and beneath the former power plant area. A summary of the results are as follows: • Waste Cell No. 1A was identified near the eastern property boundary and appears to be the continuation of the South Waste Cell. Waste Cell No. 1A is fully defined and is approximately 1,200 square feet with waste observed between four and ten feet bgs. (Note: Waste Cell No. 1, which is a continuation of the North Waste Cell, was identified and fully delineated during the previous site assessment). • Waste Cell No. 2 was previously identified beneath the east-central portion of the former power plant and is approximately 3,900 square feet with waste observed at approximately 10 feet bgs. Limited pockets of waste were encountered at three other locations beneath the former power plant • Waste Cell No. 2A was identified beneath the southwest portion of the former power plant and is approximately 10,000 square feet with waste observed between four and 12.5 feet bgs. The limits of the waste cell have not been laterally defined. • PCBs were detected above the USEPA commercial RSL of 0.97 mg/kg in nine samples collected at 3 feet bgs, nine samples collected at 5 feet bgs, four samples collected at 7 feet bgs, and two samples collected at 10 feet bgs. PCBs