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the ESD. Please ensure that the recommendations for DSERTS 67 are included in the forthcoming <br /> ESD. <br /> 4. SWMU 6,Supplemental Investigation,Page 16: The text refers the reader to a separate <br /> technical memorandum for the locations of the four soil borings completed west of the excavation, <br /> but the locations are not shown on a figure in this technical memorandum. These locations are <br /> important because they establish the limited lateral extent of residual contamination above ROD- <br /> specified cleanup standards at SWMU 6. Please include a figure showing the locations of the <br /> supplemental investigation borings. <br /> 5. SWMU 6,Modifications to the Selected Remedy,Page 17: The use of the phrase background <br /> threshold value in this section is not clear, as there is no background threshold value established <br /> for organic contaminants at DDJC-Tracy. However,the ROD does contain equilibrium <br /> partitioning limits protective of background water quality in Table 6-9. Please clarify if the <br /> reference to background threshold value for dieldrin is intended to mean the equilibrium <br /> partitioning limits protective of background water quality as defined in the ROD. <br /> 6. SWMU 6, Conclusions and Recommendations, Page 18: The recommended revised cleanup <br /> standard for dieldrin at SWMU 6 is 161 micrograms per kilogram(ug/kg),but it is not clear that <br /> this cleanup level will be protective of human health. The proposed cleanup standard exceeds the <br /> EPA Region IX Preliminary Remediation Goal (PRG)for industrial soil of 110 ug/kg. Please <br /> explain how the revised cleanup standard for dieldrin at SWMU 6 is protective of human health. <br /> In addition,please reconsider the recommendation for no institutional controls at SWMU 6,given <br /> the potential human health risks of the residual dieldrin contamination. <br /> 7. Table 5,Final DDT and Dieldrin Concentrations Exceeding ROD Soil Cleanup Standards, <br /> SWMU 8,DDJC-Tracy,and Figure 4,Residual Soil Contamination Above ROD Cleanup <br /> Standards,SWMU 8,DDJC-Tracy: The depths presented on the table differ from what is <br /> presented on the figure for every sample. Please verify the sample depths and correct the <br /> discrepancy between the table and figure for SWMU 8. <br /> 8. SWMU 8,Conclusions and Recommendations, Page 25: The maximum concentrations of DDT <br /> and dieldrin were found in sample SS0146-SO-323, which was found in a sidewall sample at either <br /> 4 or 7 feet below ground surface (bgs) The extent of residual soil contamination is uncertain <br /> because this area of the SWMU 8 excavation was never over-excavated. Please include a <br /> discussion of this uncertainty in the RARS and the subsequent ESD or ROD Amendment. Include <br /> an assessment of the potential for DDT and dieldrin to remain at SWMU 8 above concentrations <br /> protective of human health and groundwater quality. It should be noted that the data presented in <br /> the technical memorandum have not been presented in a comprehensive manner for regulatory <br /> review, so any recommendations should be tentative. <br /> 2 <br />