327 IAC 2-1-8.3 Determination of chronic aquatic criteria (CAC)

Sec. 8.3. In order to ensure that the concentration of a substance or combination of substances does not produce chronic effects on aquatic organisms, a chronic aquatic criterion (CAC) will be determined by one (1) of the following methods: (1) The following for Method 1: (A) If no CAC is given for the substance in section 6(a)(3), Table 6-1 of this rule, section 6(a)(3), Table 6-2 of this rule, or section 6(a)(5) of this rule, a CAC can be calculated using the procedures in this subdivision. (B) The CAC is derived in the same manner as the FAV in section 8.2(1) of this rule by substituting CAC for FAV, chronic for acute, MATC (maximum acceptable toxicant concentration) for LC50, SMCV (species mean chronic value) for SMAV, and GMCV (genus mean chronic value) for GMAV. (C) If chronic toxicity data are not available for at least five (5) North American freshwater genera meeting the requirements in section 8.2(1)(B) of this rule, go to subdivision (2). (2) The following for Method 2: (A) The CAC can be calculated by dividing the FAV by an acute-chronic ratio (or geometric mean of the acute-chronic ratios if more than one (1) is available) for at least one (1) North American freshwater species. (B) If no acute-chronic ratio is available for at least one (1) North American freshwater species, go to subdivision (3). (3) The following for Method 3: (A) The CAC can be calculated by dividing the FAV by a factor of forty-five (45). If, for a commercially, recreationally, or ecologically important species, the geometric mean of the chronic values is lower than the calculated CAC, then that geometric mean is used as the CAC instead of the calculated CAC. (B) If the data needed in clause (A) are not available, no CAC can be calculated and the discharger will be required to develop the minimum data base necessary to calculate the CAC (ninety-six (96) hour LC50 for rainbow trout, fathead minnow, or bluegill and a forty-eight (48) hour LC50 for a daphnid).