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Union Pacific Railroad Company - 2 - 29 November 2023 <br /> Former Bunker C Vault: Tracy <br /> aromatic hydrocarbons using EPA Method 8270, and CAM 17 metals using EPA <br /> Methods 6010B and 7471 A. <br /> Central Valley Water Board staff has the following comments regarding the proposed <br /> scope of work: <br /> 1. Central Valley Water Board staff concurs with Antea Group's proposal to <br /> collect soil samples beneath the sump using angled borings. Based on the <br /> distance from the sump and tendency for vadose zone releases to migrate <br /> vertically in soil, the proposed perimeter borings located five feet from the <br /> outside edges of the sump are not sufficient to characterize a release that <br /> occurred directly beneath it; however, the proposed perimeter borings may be <br /> included at Union Pacific's discretion to collect additional soil data outside of <br /> the sump. <br /> 2. To investigate the extent of potential releases from the former sump, each soil <br /> boring should be advanced to a depth of at least 10 feet bgs. Please be sure <br /> that the soil analysis includes samples from each boring collected at two feet <br /> below the base of the sump and at 10 feet bgs. <br /> 3. Well completion logs in the area of the Site suggest that groundwater depth <br /> may be greater than 15 feet bgs. If Antea Group does not anticipate being <br /> able to extend the angled borings to reach groundwater, please advance at <br /> least one vertical boring near the former sump to collect grab groundwater <br /> samples. <br /> 4. During a previous site investigation, Antea Group detected naphthalene <br /> concentrations in a soil sample collected from the center of the sump that <br /> exceeded the environmental screening level for leaching to groundwater. <br /> Please be sure that the upcoming investigation includes the collection and <br /> analysis of a soil sample from within the sump area for naphthalene. <br /> Additionally, any liquid found inside the remains of the sump should be <br /> characterized and removed for proper off-Site disposal, if necessary. <br /> 5. Antea Group proposed analyzing sediment and liquid samples from within the <br /> sump for polychlorinated biphenyls (PCBs) by EPA Method 8082. If there is <br /> potential for the contents of the sump to contain PCBs, the soil and <br /> groundwater investigation beneath this abandoned structure should be <br /> expanded to include analysis for PCBs as well. In addition to the proposed <br /> analytes, please analyze all soil and groundwater samples for PCBs using <br /> EPA Method 8082. <br /> Please proceed with the implementation of the Work Plan with the modifications listed in <br /> staff comments 1 through 5. By 3 May 2024, please submit a Site investigation report <br /> that includes an assessment of the risks to human health and the environment and <br /> whether the sump should be closed in place. Please be sure that the report also <br />