SITE INFORMATION AND CORRESPONDENCE_1998-2000

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`PARR ASSOCIATES Mr. Donald T. Bradshaw, R.G. October 16, 2000 Page 2 2 The latter halves of the third paragraphs on pages viii and 1 of the Draft HRA (beginning with "According to Department of Toxic Substances Control ...." must be removed because they are incorrect and misleading on important points regarding "acceptable" cleanup goals. As stated above, discussion of cleanup goals does not belong in this HRA, and is particularly premature given the lack of detailed analysis and/or discussion conducted to-date on this important topic. In addition, the California Department of Toxic Substances Control (DTSC) has formally removed Chapter 6 (including Section 6.4 cited in the subject paragraphs) from the DTSC guidance document, and LPL also believes LFR has mis-represented what DTSC said in its initially published document regarding acceptable risks. 3. The vapor transport and indoor air modeling presented in Appendix A of the HRA does not recognize residential land use as a potential future land use for the "on-Lincoln Center"exposure scenarios, as evidenced by the last sentence of the second paragraph: 11 on-site calculations used commercial exposure factors." Thus, the estimates of volatile organic compound (VOC) concentrations in indoor air presented in Appendix A are only applicable for commercial exposure scenarios. For the hypothetical on-Lincoln Center residential exposure scenarios, both the building ceiling height and the air exchange rate should be reduced, resulting in significantly greater exposure concentrations. 4 The vapor transport and indoor air modeling results predict concentrations approximately one order of magnitude lower than the concentrations that have been repeatedly observed in indoor air at Lincoln Center. The modeling analysis should be reviewed and the model revised to be consistent with existing field data. The alternate modeling equation presented by Johnson and Ettinger for diffusion-dominated transport may be useful in this regard (see additional comment below). In cases where reliable site data exist (i.e., the indoor air data referenced in the Draft HRA), such data should be trusted in preference to estimates made using heuristic modeling equations. Such data should be used to justify modeling assumptions and confirm the reliability of the chosen model(s). LPL's previous comments on this issue have been disregarded by LFR, and LFR has chosen to continue ignoring the data in favor of screening-level modeling results that are only partially site-specific. 5. Because of the shortcomings in LFR's estimated exposure-point concentrations (as discussed in Comments 3 and 4 above), LPL believes several of the estimated risks presented in the HRA are incorrect, and should be revised following the necessary revisions in the modeling analysis.