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Philip S. Isorena • April 20, 2000 Page 4 Appendix C, "PAH Concentrations Soil (mg/kg)—Representative Concentrations' also appears to contain incorrect calculations. Again, the t-value for p=0.01 instead of p=0.05 was used. The error would apply to all PAH Concentrations in Soil in Table C-4, page 5 of 6 and page 6 of 6. The error would be carried through pathways for adult and children of incidental ingestion of soil, dermal contact with soil, ingestion of homegrown produce, and inhalation of particulates. The authors are referred to Supplemental Guidance to RAGS: Calculating the Concentration Term, US EPA Publication 9285.7—081, May, 1992, and Statistical Methods for Environmental Pollution Monitoring, Richard O. Gilbert, 1987. The choice to include samples as half of the detection limit increases uncertainty in this risk assessment because there are so many samples at one-half the detection limit. Usually one-half of the detection limit is used if data showed that a particular chemical was expected to be present in a repeat sample because of its previous presence. Although a case can be made for including nondetects as representing part of the area for which the risk was estimated, the number of samples should be increased. Another concern is that the identity of the compounds that spilled or leaked is not characterized, except to say that it was fuel oil or crude oil. Methods for TPH analysis have been widely used in site characterization, but the data is unsuitable for health risk assessment because of its lack of specificity. The site contains a large concentration of petroleum products identified only as TPHg, TPHd, and TPHc and a small number of samples for which the chemical analysis was specific The authors are referred to volume 1-4 of the Total Petroleum Hydrocarbon Criteria Working Group Series, which can be found at http://www.aehs.com/ASP/publications/onlineTPHbooks.htnil. Conclusion: There is too much uncertainty due to insufficient sampling and chemical specific analysis, errors in calculating 95%UCL, and the choice of the vapor intrusion model to have confidence in the estimated human health risk. The authors are referred to the U.S. EPA Guidance for Data Useability in Risk Assessment, April 1992, which states, "Data needs for baseline risk assessments are not necessarily met by data the Remedial Project Manager acquires to identify the nature and extent of contamination. For example, a sampling strategy designed to determine the boundaries of a contaminated area may not provide data to quantitate concentrations within an exposure area. The risk assessor may also require more precision and accuracy, and lower detection limits." (p. 25)