Illinois EPA grants Exelon LaSalle Station Provisional Variance from Discharge Requirements

Springfield—The Illinois Environmental Protection Agency (IEPA) has granted the Exelon Generation’s LaSalle County Power Station a provisional variance from the National Pollutant Discharge Elimination System (NPDES) water discharge permitted temperature limits, due to recent unseasonably warm weather conditions

LaSalle Station is an electric generating facility located in southeastern LaSalle County, six miles southeast of Marseilles. Circulating water used to cool and condense steam from the generating process is discharged into the Illinois River. 

LaSalle Station’s NPDES permit places limits on the temperature of the effluent versus the temperature of the river water during a given season, and gives the facility an allowance of excursion hours it can use if its discharge exceeds the temperature. Because of recent record breaking warm weather, the river temperature at the intake has already exceeded the maximum temperature standard. Without this provisional variance, LaSalle Station will be forced to stop the blow down of water from its cooling pond which, in turn, may compromise the integrity of the pond’s exterior dikes.


During the variance period, LaSalle Station must continuously monitor both discharge and receiving water temperatures and must visually inspect all discharge areas at least three times each day to assess the impact on aquatic life.   It must also notify the Illinois EPA and the Illinois Department of Natural Resources if aquatic life is shown to be affected. If the increased discharge temperature results in adverse environmental impact, appropriate reparations must be conducted.

Exelon LaSalle Power Station must continue to meet all other effluent conditions in its NPDES permitalong with additional conditions contained in the provisional variance but not expressly listed above. 

The Illinois EPA has determined that any environmental impact from the variance would be closely monitored, and the Agency will be notified immediately of any adverse impacts; no reasonable alternative appears to be available; no public water supplies will be affected; no federal regulations would prohibit granting the request; and the facility would face an arbitrary and unreasonable hardship if the IEPA did not grant the requested variance. 

The provisional variance will be in effect no later than March 31, 2012. All other NPDES permit requirements will remain in effect.

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