Our client’s coal-fired power plant utilizes once-through cooling and discharges heated water to Lake Superior. An update to the facility’s NPDES discharge permit required a thermal plume verification study to characterize the thermal plume, describe the local biotic community, and confirm that the thermal discharge does not have an adverse effect on fish and other organisms.
LimnoTech developed a cost-effective study that maximized the use of existing data and cutting-edge technology. Our approach for characterizing the thermal plume incorporated temperature data collected in the field, satellite imagery, infrared photography, and a three-dimensional thermal plume model of Lake Superior in the vicinity of the facility. The thermal plume model characterized the complex conditions in the study area, including multiple facility outfalls and the influence of a nearby river that contributes warm water near the facility outfall. Temperature output from the model was compared to thermal tolerance information for local fish species to evaluate potential impacts on biota. The approach used to characterize the thermal plume allowed us to evaluate a greater range of water and operational conditions compared to what would have been possible with only traditional field methods.
The study found that heat released from the facility dissipates quickly, and only marginally warms the ambient waters in the immediate vicinity of the discharge. Even under worst case conditions, the size of the thermal plume is very small, and unlikely to have a detrimental effect on the local aquatic community. Documentation of the study and the results were submitted to the State NPDES permitting agency in fulfillment of the client’s permit requirements. Our work demonstrates that aquatic organisms are adequately protected in the study area over a wide range of environmental conditions, and the facility does not need to modify its operations.