SITE INFORMATION AND CORRESPONDENCE_1993-2003

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w Cori L. Condon - 3 - 29 August 1997 • Page B-4,14. EPA has classified PCE in weight-of-evidence category B2 or probable human carcinogen. The ATSDR report incorrectly labels PCE as a probable or possible human carcinogen. • Page B-5, $ 1. The California Primary MCL for 1,2-DCA is 0.5 µg/1,not 5 µg/l. Measured concentrations of 1,2-DCA in private off-site wells have significantly exceeded this drinking water standard. • Page B-5,$ 1. The report discusses MCLs as "enforceable." Primary MCLS are enforceable drinking water standards for chemicals in water distribution systems and at the tap. In groundwater and other ambient waters,water quality objectives from the applicable Basin Plan are part of the enforceable water quality standards. By reference, Primary and Secondary MCLS are a subset of the enforceable water quality standards for chemical constituents in groundwater in the area of DDRW 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. • Page B-5, $ 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. • 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. • Appendix B. No analysis is presented of the health risks posed by TCE. • 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. .%