Guest Column: The impact of thermal discharges in the Mississippi River

By Olivia Dorothy
Regional Conservation Coordinator, Upper Mississippi River Initiative, Izaak Walton League of America

One month ago, the Quad Cities Generating Station submitted a request to the Illinois Pollution Control Board to relax some of the nuclear plant’s thermal discharge standards during the summer months (case No. PCB 2014-123). This proposed rule change is interesting on several levels, and I’m having a hard time deciding how to approach this proposed rule. Full disclosure, the Izaak Walton League receives substantial funding from Exelon’s Quad Cities Generating Station for our Midwest operations.

But, beyond the obvious conflict of interest, the proposed rule change highlights an interesting dilemma. The Generating Station cannot continue to operate within the limits of its permits as the dynamics of the Mississippi River change with the climate. As global average temperatures increase, the weather pendulum in the Midwest swings more dramatically. As predicted, we are seeing longer droughts punctuated by intense storms that cause more frequent flooding and all the other damages associated with severe weather.

The droughts are the big concern for the Quad Cities Generating Station, which discharges hot cooling water directly into the Mississippi River, where normal and high flows quickly dilute the thermal discharge. But, as we are seeing drier, hotter summers, the Generating Station cannot stay within the confines of its discharge permits. The station is asking the Pollution Control Board to permit hotter water to be discharged during the summer months — permitting water up to 91 degrees Fahrenheit to be released for up to 131.4 hours during those dog days. This is 3 degrees hotter than the current standards.

How might this impact wildlife on the Mississippi River? Thankfully, the Generating Station houses an aquatic research program that monitors the fish and wildlife impacts from station operations. In 2006, after a particularly hot, dry year with many permit violations, the aquatic research program launched a study on the short- and long-term mussel community impacts of that hot, hot year.

Mussels have been a part of the station’s aquatic monitoring program for several years, so comparative data going back to 2004 is readily available. Overall, mussel communities both up and downstream of the thermal discharge location declined in 2006, but populations obviously start to recover in 2007, indicating that long-term impacts as a result of occasionally hot summers are probably negligible. Strangely, the federally endangered Higgins eye mussel actually did better than the other populations in 2006 — especially in the downstream Cordova bed that is part of the Fish and Wildlife Service Higgins eye recovery plan.

CAUTION! We should not conclude that warmer water temperatures will restore the Higgins eye mussel population — especially since all the other mussel populations declined! A number of other factors could be influencing the Cordova bed population. For example, studies from the generating station show substrate temperature does not track neatly with water temperature — substrate temperature could be influencing the population. Or, it could be something else, or a combination of other factors.

But, as the Mississippi River’s water gets hotter — especially in the spring and fall, as John Chick documents in Pool 26 — we need to ask a big question: How can we protect and restore the dammed, dredged and leveed Mississippi River while the climate changes faster than we can adapt?

If you want more information about the Quad Cities Generating Station aquatic studies, contact Jeremiah Haas at

A Decade of Monitoring on Pool 26 of the Upper Mississippi River System,” by John Chick, et. al., abstract and full citation is available at

From the May 14-20, 2014, issue

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