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Cori L. Condon - 3 - 15 December 1997 Sharpe. Narrative objectives prohibiting toxicity, adverse tastes and odors, and interference with beneficial uses are equally enforceable water quality standards for groundwater in this area. This issue is not addressed or even acknowledged in the revised draft report. • Page B-5,1 2. EPA has classified 1,2-DCA in weight-of-evidence category B2 or probable human carcinogen. The ATSDR report incorrectly labels 1,2-DCA as a probable or possible human carcinogen. The report has been. corrected in response to this comment. • Page B-5,$ 2. The basis for ATSDR's cancer risk estimate for 1,2-DCA is not presented. As discussed above, a lifetime cancer risk estimate calculated from the highest measured concentration of 1,2-DCA,using Cal/EPA's cancer potency factor, is 4 x 10"5. If USEPA's cancer potency factor is used, the lifetime risk is 5 x 10-5. This issue has not been addressed. • Appendix B. No analysis is presented of the health risks posed by TCE. A TCE section was added on page B-5. The discussion of ATSDR's 10"6 cancer risk evaluation guide (CREG) is incorrectly placed within the "noncancer'subsection (as is the case with the discussion of the cancer risk based MCL for 1,2-DCA at the bottom of page B-5 and the CREGs for PCE and arsenic at the top of page B-4 and the bottom of page B-2, respectively). The highest measured concentration of TCE in off-site domestic wells is above ATSDR's CREG (10-6 cancer risk level); however, the report states that ATSDR's estimated risk from this concentration is 4 x 10"7, a risk lower than 10"6. ATSDR appears to be manipulating even its own risk calculation methods, resulting in downgrading the apparent risk. • Appendix B. No analysis is presented of the cumulative health risks posed by multiple chemicals found together in water samples. Table 6 on page 33 shows two probable human carcinogens to have been present in two of the tested wells. A section on the combined risk of exposure to PCE and TCE has been added on pages B-6 and B-7. The estimated risk level stated in the report is lower than if it had been calculated using Cal/EPA OEHHA cancer potency factors and lifetime cancer risk estimation methods.