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Former San Joaquin Cogeneration - 3 - 29 December 2020 <br /> Lathrop, San Joaquin County <br /> WET) method and found low leaching potential of 0.0042 milligrams per liter <br /> (mg/L). <br /> • Arsenic was detected in soil samples and waste samples at a maximum <br /> concentration of 13.5 mg/kg, exceeding the commercial ESL of 0.32 mg/kg. <br /> • Hexavalent chromium was detected in several groundwater samples at <br /> concentrations ranging from 0.93 micrograms per liter (ug/L) 8.4 ug/L. Although <br /> there is currently no drinking water Maximum Contaminant Level (MCL) for <br /> hexavalent chromium, the detections are below the previously proposed MCL of <br /> 10 ug/L. <br /> • Arsenic, selenium, ammonia, nitrate as nitrogen, and nitrate as nitrate collected <br /> was detected at concentrations exceeding screening levels in one or more grab <br /> groundwater samples. <br /> • A maximum concentration of 2,590 mg/L of total dissolved solids (TDS) in boring <br /> B1 exceeds the MCL of 500 mg/L. <br /> Additional Site Assessment Summary <br /> Between 22 and 25 June 2020, AGI conducted additional site assessment activities at <br /> the Site including advancing 36 soil borings (B44 through B79) to depths ranging from <br /> two feet bgs to 20 feet bgs, collecting soil samples from multiple depths for analysis, <br /> and collecting grab groundwater samples from five of the borings for analysis. The <br /> objective of the additional assessment activities was to define the lateral and vertical <br /> extent of the PCB- and TPH-impacted soil and waste material beneath the South Waste <br /> Cell, which extends into the eastern portion of the Site, and beneath the former power <br /> plant area. A summary of the results are as follows: <br /> • Waste Cell No. 1A was identified near the eastern property boundary and <br /> appears to be the continuation of the South Waste Cell. Waste Cell No. 1A is <br /> fully defined and is approximately 1,200 square feet with waste observed <br /> between four and ten feet bgs. (Note: Waste Cell No. 1, which is a continuation <br /> of the North Waste Cell, was identified and fully delineated during the previous <br /> site assessment). <br /> • Waste Cell No. 2 was previously identified beneath the east-central portion of the <br /> former power plant and is approximately 3,900 square feet with waste observed <br /> at approximately 10 feet bgs. Limited pockets of waste were encountered at <br /> three other locations beneath the former power plant <br /> • Waste Cell No. 2A was identified beneath the southwest portion of the former <br /> power plant and is approximately 10,000 square feet with waste observed <br /> between four and 12.5 feet bgs. The limits of the waste cell have not been <br /> laterally defined. <br /> • PCBs were detected above the USEPA commercial RSL of 0.97 mg/kg in nine <br /> samples collected at 3 feet bgs, nine samples collected at 5 feet bgs, four <br /> samples collected at 7 feet bgs, and two samples collected at 10 feet bgs. PCBs <br /> were not detected in samples collected beneath 10 feet bgs. The highest PCB <br />