1. (a) General. Complete mixing of effluent and receiving water shall be used to determine appropriate permit limits. A mass balance model shall be used for implementation purposes.

2. (b) Determination of reasonable potential factor.

   1. (1) The mass balance equation will be used in the determination of human health reasonable potential: C = (C_eQ* + C_B) / (Q* + 1). Q* = Q_e/Q_u, where Q_e is the regulatory effluent flow. C must be considered a long-term average concentration after complete mixing. C_B is the background concentration. To determine if there is a reasonable potential to exceed the criterion after complete mixing, choose C_e = 2.13C_mean, where C_mean is a geometric mean of all effluent concentrations analyzed for the toxicant. If the geometric mean cannot be determined, an arithmetic mean may be used instead.
   2. (2) Representative background concentrations will be used if available. Such representative data should reflect long-term average pollutant concentrations for implementation purposes. Otherwise, C_B is assumed zero.
   3. (3) C must be compared with the applicable water quality criterion to determine if there is a reasonable potential for the pollutant discharge to cause a criterion exceedance. If concentration after complete mixing is greater than the human health criterion, a permit limit will be required.

Added at 40 Ok Reg 329, eff 10-25-22 (emergency)

Added at 40 Ok Reg 2062, eff 9-15-23

Amended at 41 Ok Reg, Number 23, effective 9-15-24