# Mich. Admin. Code R. 323.1211 - Reasonable potential for chemical-specific water quality-based effluent limits (WQBELs)

Rule 1211**.**

P95 = exp (mudn + Zp sigmadn)

Where: P95 = upper ninetififth percentile of n-day average discharge concentrations.

d = ratio of the number of daily discharge concentrations less than the limit of detection to the total number of discharge concentrations.

n = number of discharge concentrations used to calculate an average over a specified monitoring period (n=1 for daily concentrations and 30 for 30- day averages).

exp = base e (or approximately 2.718) raised to the power shown between the parentheses in the P95 equation.

Zp = Z value corresponding to the upper
p^{th} percentile of the standard normal
distribution.

p =
(0.95-d^{n})/(1-d^{n}).

Click Here To View Image

Click Here To View Image

ln = natural logarithm.

m = mean of discharge concentrations greater than the limit of detection.

s = standard deviation of discharge concentrations greater than the limit of detection.

Reasonable potential for the discharge of a toxic substance to cause or contribute to an excursion above any water quality value will be considered to exist if the average or maximum PEQ exceeds any of the chronic or acute PELs, respectively, developed in accordance with subrule (2) of this rule.

Table 4. Reasonable potential multiplying factors: 95% confidence level and 95% probability basis.

Number of Samples | |||||||||

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |

Multiplying Factor | 6.2 | 3.8 | 3.0 | 2.6 | 2.3 | 2.1 | 2.0 | 1.9 |

1.8 | ||||||||

10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |

19 | ||||||||

1.7 | 1.7 | 1.6 | 1.6 | 1.5 | 1.5 | 1.5 | 1.4 | 1.4 |

1.4 | ||||||||

20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |

1.4 | 1.2 | 1.1 | 1.0 | 1.0 | 0.9 | 0.9 | 0.9 | 0.9 |

Monitoring frequency to evaluate compliance with WQBELs shall be established by the department on a case-by-case basis.

Note: The Water Quality Guidance for the Great Lakes System, 40 C.F.R. Part 132 (1995), indicates that a permit may not authorize no net addition limits that are effective after March 23, 2007. The preamble to 40 C.F.R. Part 132 indicates that the environmental protection agency (EPA) will revisit this requirement by March 23, 2002, to consider possible extensions. After the redetermination by EPA, the department will consider modifying these rules to incorporate a phaseout date for no net addition limits, if still necessary.

## Notes

State regulations are updated quarterly; we currently have two versions available.
Below is a **comparison between our most recent version and the prior quarterly release.**
More comparison features will be added as we have more versions to compare.