Determining the Chronic Aquatic Toxicity Criterion - Procedure for Combinations of Substances

Section 302 Section 302.630  Determining the Chronic Aquatic Toxicity Criterion - Procedure for Combinations of Substances A CATC for any combination of substances (including effluent mixtures) may be determined by toxicity testing procedures pursuant to the following: a)         A combination of substances must not exceed concentrations greater than a NOAEL as determined for the most sensitive of the species tested. b)         Three resident or indigenous species of ecologically diverse taxa must be tested initially.  If resident or indigenous species are not available for testing, non-resident species may be used if the non-resident species is of the same family or genus and has a similar habitat and environmental tolerance.