(1) If, in performing a toxicity identification/reduction evaluation, four consecutive acute or chronic toxicity samples taken over at least one month are not sufficiently toxic to perform the toxicity identification/reduction evaluation, then the department may approve the interruption of the toxicity identification/reduction evaluation and require that:

(a) The permittee returns to the monitoring frequency specified in the permit.

(b) Sufficient sample volume be taken each time to allow the lab to perform both a toxicity test and begin a toxicity identification/reduction evaluation.

(c) The extra sample shall be stored at four degrees Celsius in the dark while the toxicity test is being performed.

(d) A toxicity identification/reduction evaluation shall begin as soon as the whole effluent toxicity test demonstrates noncompliance with the limit.

(e) Samples may be discarded from storage after completion of the toxicity test if the whole effluent toxicity limit was not violated.

(2) If toxicity testing shows compliance with whole effluent toxicity limits for one year after interruption of the toxicity identification/reduction evaluation, then the permittee may cease taking the extra sample.