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• i <br /> needed to calculate PBGs. A list of expected contaminants <br /> for which no toxicity information is readily available <br /> through the Integrated Risk Information System (IRIS) or the <br /> Health Effects Summary Tables (HEAST) should be submitted at <br /> this time, to allow adequate time for toxicity values to be <br /> developed for the BRA. Human health risk at ARARs is <br /> calculated using AKAR concentrations as exposure point <br /> concentrations in risk equations, using standard default <br /> exposure factors. PRGs can be calculated for each <br /> contaminant by using a rearrangement of the same equations. <br /> The results of the PBGs should be summarized in a tabular <br /> format. An example of PRGs for water and their comparison <br /> to reported analytical detection limits is provided in Table <br /> 1. (Note that some of these detection limits are grossly <br /> inadequate. ) <br /> 2 . The BRA Work Plan for the Comprehensive RI/FS (May 1992) <br /> intends to "utilize and incorporate" information from the <br /> BRA for Operable Unit #1 (OU #1) . However, DDRW-Tracy <br /> should not use this information to limit the investigation <br /> of chemicals of potential concern and exposure pathways. <br /> 3 . A list of chemicals of potential concern (approximately 30) , <br /> are prematurely used as the starting point for the selection <br /> of chemicals of concern. The list of chemicals of potential <br /> concern should include all chemicals that are analyzed for C— <br /> during the Phase I sampling (Appendix A: Field Sampling <br /> Plan) . There exists no rationale at this point for limiting <br /> potential chemicals of concern. <br /> ADDITIONAL SPECIFIC COMMENTS <br /> 1. Page 4-1, Section 4 . 0, Heading <br /> This heading should read "Baseline Risk Assessment" rather <br /> than "Risk Assessment. " EPA suggests "baseline risk <br /> assessment" be used in place of "risk assessment. " <br /> 2 . Page 4-1, Section 4 . 1. 1, Paragraph 1. Sentence 2 <br /> This sentence should read "the objective of the BRA is to <br /> evaluate actual and future risk to human health and the <br /> environment posed by DDRW-Tracy in the absence of remedial <br /> action. " <br /> 3. Page 4-1, Section 4 . 1.2 , Paragraph 2 <br /> The BRA does not determine remedial action goals nor <br /> acceptable risk, but rather it presents an objective <br /> analysis of the actual and potential risks to human health <br /> and the environment posed by DDRW-Tracy. <br /> II-2 <br />