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Tori o - ,--2 4 -,,1 I j' } J with the health effects information developed unaer the R[-1CL process Tnus primary MCLS are not necessarily a relia.Dle indicator of protection c, an ambient water resource and should not be relied upon as water quality Goals in cleanup situations. Discussion: Chloroform is a potential human carcinogen. The International Agency for Research on Cancer (IARC) evaluates the strength of the evidence for carcinogenicity of substances and pubs fishes those evaluations in their „monographs". The IARC defines chioroforrn as 2 C~ miCui f r ';rhiC l t",ere is sufficient evidence of carcinogenicity in experimental animals.,, 2 For. comparison, the IARC does not find that such "sufficient evidence" exists for trichloroethylene (TCE). In a 1980 IARC publication, TCE was categorized as a chemical "with very strong evidence for carcinogenicity in one species and no evidence in a second species." The same publication categorized chloroform as a chemical "with very strong evidence (to an unusual degree and/or in multiple experiments) for carcinogenicity in two animal species." 3 It is clear that the cancer risk data for chloroform is more reliable as an indicator of potential human carcinogenicity than that for TCE. In 1980, the U.S. EPA published a document entitled Ambient Water Quality Criteria for Chloroform 1, in which the following criteria for human health protection were provided: "For the maximum protection of human health from the potential carcinogenic effects due to exposure of chloroform through ingestion of contaminated water and contaminated aquatic oraanisms, the ambient water concentrations should be zero based on the non -threshold assumption for this chemical. However, zero level may not be attainable at the present time. Therefore, the levels which may result in incremental increase of cancer risk over the lifetime are estimated at 10-5, 10-6, and 10-7. The corresponding recommended criteria are 1.90 ug/l, 0.19 pg/l, and 0.019 fig/1, respectively." EPA has also established a 10-6 cancer risk level for TCE of 4.5 kg/1.4 DHS endorsed this value by promulgating their "action level" for TCE at 5 pg/1 5, and is using this value in ground water cleanup cases. EPA more recently establish a drinking water RMCL of "zero" for TCE (federal statutes mandate