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Peter MacNicholl • • 11 April 2007 <br /> Dieldrin in Groundwater at Tracy Depot Page 3 <br /> CONCLUSION AND RECOMMENDATIONS <br /> 1. The assessment is incomplete, because the maximum detected concentration of dieldrin was <br /> not used as the exposure point concentration. <br /> 2. If the maximum value had been used, cancer risk would have been—2 E-4 and the non-cancer <br /> hazard index would have been —1.6. Dieldrin should be retained as a chemical of concern in <br /> groundwater. <br /> 3. The 95UCL was calculated incorrectly, because duplicates were included and because non- <br /> detects were not properly accounted for. <br /> 4. After making the necessary corrections and using ProUCL 4.0, the recommended 95UCL is <br /> 0.041 µg/L. If the 95UCL is needed for any regulatory or risk management decisions, the <br /> value of 0.041 ltg/L should be used. <br /> Reviewed by: Michael J. Wade, Ph.D., D.A.B.T. <br /> Senior Toxicologist, HERD <br /> REFERENCES <br /> Helsel, Dennis R. (2005),Nondetects and Data Analysis, John Wiley & Sons, Hoboken,NJ. <br /> USEPA (2002), "Calculating Upper Confidence Limits for Exposure Point Concentrations at <br /> Hazardous Waste Sites", U. S. Environmental Protection Agency, Office of Solid Waste and <br /> Emergency Response, December 2002„ http://www.epa.Ezov/oswer/riskassessment/l)df/ucl.pdf. <br />