“We remain committed to working with the Sierra Club as we transition to a cleaner energy future without putting our customers’ comfort or lives at risk,” Conway continued. “Unfortunately, the Sierra Club’s suggestion that we retire our fossil plants immediately is premature and impractical.”

New and lower discharge caps

The revised permit also lowered the discharge variance from 4.1 parts per trillion to 3.7 parts per trillion, “setting the first-ever cap on mercury from the outfall.”

“The cap will serve as a backstop to prevent an increase in mercury loading from (Oak Creek Power Plant) until it is brought into compliance with the monthly average wildlife water quality criterion of 1.3 parts per trillion,” the release stated.

In the DNR’s response to public comments on the permit, it sites one commentator who notated that there are methods, though experimental, for removing mercury from water, making discharge below 1.3 ng/L, which is considered the floor for this type of disposal, theoretically possible. The department said it reached out to other entities to learn about these methods but “they did not provide documentation or studies demonstrating consistent attainment for this types of wastewater as requested.”