Skip to main content

An affiliate of Wisconsin Manufacturers & Commerce

Wisconsin Thermal Discharge Rule (CR07-111)

Most Recent Action


Guidance for Implementation of the Thermal Water Quality Standards is available for viewing and comment, December 22, 2010


The final rulemaking order was filed on August 5, 2010.




The Department is currently operating under existing requirements of ch. NR 102, Wis. Adm. Code, that took effect on October 1, 1973. However, the Wisconsin Supreme Court declared significant portions of ch. NR 102 invalid (Wisconsin Electric Power Company v. Wisconsin Natural Resources Board, 90 Wis. 2d 656 (1979)), so specific guidelines are not clear.


The EPA requires thermal limits to be included in appropriate National Pollutant Discharge Elimination System (NPDES) permits to meet federal law and regulations. In the absence of state rules, the EPA has the authority to directly regulate discharges of heat under the NPDES permit program, and has indicated intent to do so.


The DNR has been working on revisions to the thermal standards in NR 102 since 1994 when an advisory committee was formed. An initial draft rule was authorized for public hearing in 1998 and additional advisory committee work continued until 2007. In early 2008 a revised rules was sent to public hearing.


The Natural Resources Board adopted the revised standards on January 27, 2010. Neither the Senate nor Assembly standing committees took action on the package.




Sections 281.15 and 283.13, Stats., authorize the Department to establish appropriate thermal water quality standards and associated water quality-based effluent limitation calculation procedures for heated discharges to surface waters of the state. Section 283.17, Stats., provides the Department the authority to establish thermal effluent limitation modification procedures.




Final Proposed Rulemaking Order – Two chapters of the Wisconsin Administrative Code were modified during this rule revision effort. Chapter NR 102 was revised to create water quality standards for heat in surface waters. Chapter NR 106was revised to include procedures to implement the thermal standards in Wisconsin Pollutant Discharge Elimination System (WPDES) permits issued to point sources discharging to surface waters of the state. (Note: Chapter NR 209 will be repealed and re-created as Sub-chapter VI of NR 106.)


Temperature restrictions are based upon the receiving water body’s ability to assimilate heat. Therefore, the ratio of the flow for the discharge to the flow of the receiving water body will determine the maximum temperature of any given facility’s effluent.




The impact of the proposed rule on regulated facilities will vary depending on the classification of the water body – ranging from more stringent temperature limits to no limit at all. Additionally, some sources that have had thermal limits may not require one under the proposed rule and some sources will be required to have thermal limits even though they have not had one in the past.


The proposed rule provides two basic options to determine the ambient water quality standards that must be met by a discharge.

  • Table Values – Proposed NR 102.25
    • Determine stream classification for receiving stream – cold water, warm water, or limited forage fish to obtain the ambient water quality temperature.
    • Tables determine sub-lethal maximum (weekly average) and acute maximums (daily maximum) for each month of the year.
    • Different tables exist for specific large rivers, non-specific rivers, inland lakes, and Great Lakes
  • Site Specific Values – Proposed NR 102.26
    • Determine ambient water quality temperature based on in-stream monitoring data through methodologies defined by rule.
    • Tables determine sub-lethal and acute maximum temperatures depending on the ambient temperature by month.
  • Exception for various bodies of water – Proposed NR 106.55

Once the water quality standard is determined, translating that standard into an effluent limit requires several discretionary determinations.


Related Documents


Guidance for Implementation of the Thermal Water Quality Standards

An Excel spreadsheet that allows interested parties to calculates Water Quality-Based Effluent Limitations (WQBELs) using facility-specific effluent flows and temperature information is available on this DNR website.


Thermal Rules Revisions Frequently Asked Questions


Initial Proposed Rulemaking Order


Clearinghouse Review of Rule


Report to Legislature


Final Rulemaking Order Filed


Summary of Economic Impact and Legislative Review