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Thermal water quality standards

Thermal pollution is the change in the water temperatures of lakes, rivers and other surface waters caused by man-made practices. These temperature changes may adversely affect fish and aquatic life in Wisconsin's surface waters by reducing the reproductive success of fish and aquatic life, contributing to habitat degradation and, in extreme cases, causing fish kills. Human health, domestic animals and wildlife may also be at risk if water temperatures are sufficiently high to cause scalding.

Protecting human health and welfare

To protect human health and welfare, revisions to Wisconsin's Thermal Water Quality Standards for surface waters were adopted on Oct. 1, 2010. 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 106 was revised to include procedures to implement the thermal standards in WPDES permits issued to point sources discharging to surface waters of the state.

Implementing thermal standards in WPDES permits

Any surface water discharge with a WPDES permit may be subject to thermal regulations. This includes industrial, municipal and wastewater discharges. Guidance for Implementation of Wisconsin's Thermal Water Quality Standards is available to provide WPDES permittees as well as other interested entities with guidance on how to implement thermal standards in WPDES permits. This document provides guidance on several subjects including effluent temperature monitoring, how to calculate limits, compliance determinations and options for compliance flexibility.

Water Quality-Based Effluent Limitations (WQBELs)

The DNR calculates and determines the need for temperature limits upon permit reissuance. If you represent a surface water discharge and are interested in calculating limits prior to permit reissuance, contact your local basin engineer or specialist.

Options for flexibility

Several options are available to adjust or provide relief from the acute and sub-lethal temperature limits. These include:

  • using monthly, updated receiving water flow rate (Qs);
  • requesting a larger fraction of the receiving water flow rate used to calculate limits;
  • increasing the size of the mixing zone;
  • requesting a site specific ambient temperature;
  • pursuing an alternative effluent limitation for temperature; and
  • developing a site-specific temperature criteria.

Each of these options is described in the thermal guidance document (Chapters 9-15).

Another option available to municipal wastewater discharges is called "dissipative cooling." Dissipative cooling is frequently a straightforward compliance option that allows municipal discharges to drop sub-lethal temperature limits by accounting for rapid heat loss that occurs in the environment. Dissipative cooling demonstrations typically require some amount of effluent and in-stream temperature data collection. See Chapter 11 of the thermal guidance document for additional guidance.

Once you have completed the dissipative cooling study, submit the Dissipative Cooling Request (Form 3400-198) to your local DNR wastewater engineer or specialist.