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Wisconsin Natural Resources Board Approves Thermal Discharge Rules

Environmental Law Update Thomas P. McElligott, David A. Strifling, Raphael F. Ramos

On May 27, 2009, the State Natural Resources Board adopted thermal discharge rules ("the Rules") proposed by the Wisconsin Department of Natural Resources ("DNR"). The Rules establish thermal water quality standards and the procedures for translating those standards into permit effluent limitations. The Rules give the DNR broad authority to impose thermal effluent limitations for the first time since 1979.1

The practical effect of the Rules is that any facility discharging effluent at a higher temperature than the receiving water body may face additional effluent limitations in its next round of permitting and may have to incur additional compliance costs. Several factors will play into what steps, if any, a facility must take to ensure compliance. For example, facilities discharging into water bodies with high rates of flow will typically have an advantage over those that discharge into low flow or standing waters because water bodies with a high rate of flow can more easily assimilate heat. As such, facilities will have to take their individual site circumstances into account when attempting to interpret the Rules.

Specifically, the Rules allow the DNR to regulate effluent temperature based on two things: the type of water body receiving the discharge and the flow rate of that water body. NR 102 will contain the thermal water quality standards for various water bodies while NR 106 will contain the methodology for calculating the limits on thermal discharges. To prevent human injury via scalding, the Rules include a hard limit of 120ºF. In calculating additional limits, the DNR has adopted a "Flow-Ratio" approach. This approach takes the flow rate of the heated discharge and compares it to the flow rate of the receiving water body.2 Depending on the ratio, the DNR may impose additional limits, based on a complicated formula using acute and sub-lethal standards in NR 102.

In addition, the Rules provide for numerous site-specific standards and alternate effluent limitations available on a case-by-case basis. Grant of an alternative effluent limitation will depend on "relevant evidence," including historical information showing that a less stringent standard would suffice. Because of the significant costs associated with compliance, many facilities will likely pursue these site-specific standards or alternative effluent limits to avoid constructing expensive cooling towers or undertaking other alternative means of reducing the temperature of its effluent.

The Rules are now subject to legislative review from standing committees in the State Senate and Assembly. Should the Rules survive review from both houses without objection, they will be deemed approved by default.

The Final Rules and accompanying Greensheet are available at For more information, please contact Tom McElligott at 414-277-5531 / [email protected], Dave Strifling at 414-277-5527 / [email protected], Raphael Ramos at 414-277-5539 / [email protected] or your Quarles & Brady attorney.

In 1979, the Wisconsin Supreme Court struck down then-existing thermal discharge rules and left the DNR with few options for addressing effluent temperature. WEPCO v. State Natural Resources Board, 90 Wis.2d 656, 280 N.W.2d 218 (1979) (striking down the thermal rules for exceeding federal categorical limits without any basis in water quality).
2The Flow-Ratio approach compares the flow rate of the receiving water body (calculated as 1/4 of the average minimum seven-day flow occurring once every 10 years or, alternatively, 1/4 of the flow which prevents an excursion from applicable water quality criteria over four days and a frequency of less than three years) to the flow rate of the discharge (the highest daily maximum flow that has occurred for each calendar month of the year).
3Minor revisions were made during approval to correct typographical errors and to clarify that the acute standard applies both inside and outside of the mixing zone.