Section 352.520  Whole Effluent Toxicity Data

When assessing reasonable potential to exceed, WET data shall be characterized consistent with the following:

a)         When multiple acute toxicity values for individual species are available for a single day, those values shall be averaged to represent one daily value. The maximum of all representative daily values for the most sensitive species tested shall be used for determination of potential to exceed the acute toxicity standard.

b)         When multiple chronic toxicity values for individual species are available for a single calendar month, those values shall be averaged to represent one monthly value.  The maximum of all representative monthly values for the most sensitive species tested shall be used for determination of reasonable potential to exceed the chronic toxicity standard.

c)         When there is insufficient WET data to adequately characterize the toxicity of the effluent to aquatic life, in lieu of a WET limit the Agency will include one or both of the following provisions in the permit:

1)         WET testing requirements to generate sufficient data to adequately characterize the toxicity of the effluent;

2)         A permit reopener clause  which authorizes the Agency, based upon the results of the WET tests required under subsection (c)(1), to establish toxicity reduction evaluation requirements, or WET limits, or both, if necessary to meet the toxicity standard, and a compliance schedule if appropriate.