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ATTACHMENT II <br /> BASELINE RISK ASSESSMENT <br /> EPA COMMENTS ON <br /> DDRW-TRACY'S <br /> DRAFT LETTER REPORT OF 10/30/91 <br /> GENERAL COMMENTS <br /> In general, the responses indicate that most of our comments on <br /> the initial baseline risk assessment should be addressed in the <br /> revised baseline risk assessment for both Operable Unit No. 1 (OU <br /> No. 1) and the Remedial Investigation/Feasibility Study (RI/FS) <br /> for the DDRW-Tracy site. Because of this, the responses did not <br /> provide details on how specific issues will be resolved. Thus, <br /> it is difficult to ascertain whether the issues will be addressed <br /> properly. It would have been more useful if DDRW-Tracy had <br /> provided detailed responses to the review comments. <br /> Also, because of the lack of detail in the responses, EPA cannot <br /> evaluate the specific methodology that will be used to address <br /> and incorporate our comments in the revised baseline risk <br /> assessment. EPA cannot ascertain whether the changes DDRW-Tracy <br /> plans to make will be acceptable. <br /> Revised Risk Assessment <br /> There seems to be some misunderstanding in this paragraph between <br /> Risk Assessment Guidance for Superfund (RAGS) and Superfund <br /> guidance for Region 9 . RAGS is national guidance for conducting <br /> a human health risk assessment under Superfund and provides a <br /> number of general exposure parameters. EPA Region 9 has <br /> developed guidance of exposure parameters to be used in risk <br /> assessments performed in Region 9. Region 9 guidance is separate <br /> yet complementary to RAGS. <br /> Subtask A: Sten 1 Hazard Identification <br /> Both RAGS and EPA Region 9 guidance prefer not to narrow down the <br /> chemicals to a list of chemicals of concern unless the original <br /> list is very cumbersome. Also, if such narrowing is acceptable, <br /> a limit of 6-8 chemicals should not be imposed prior to the <br /> assessment. An indication of the methodology to be used for the <br /> selection of chemicals of concern (both organic and inorganic <br /> compounds) should be presented. RAGS considers the use of the <br /> 95% confidence limit for the arithmetic mean adequate for the <br /> reasonable maximum exposure (RME) scenario. Finally, the term <br /> "Hazard Identification" is outdated and is no longer used in <br /> RAGS. <br /> II-1 <br />