A 1999 lawsuit found Cinergy (now Duke Energy) guilty of modifying the plant from 1989 to 1992 without installing the best-available pollution control technology. The judge shut down the units, citing increased sulfur dioxide emissions.

Duke Energy shut down the units, as required, by Sept. 30, 2009. They are appealing this decision.

Some observant individuals may remember a periodic sickly sweet furnace odor in Terre Haute, which was most pronounced during the winter months. This air pollution was from these old power generating units. The air in Terre Haute is noticeably cleaner with these old units offline.

Another major polluter was Wabash Environmental Technologies, which was shut down in 2003 by the EPA for polluting the Wabash River. And the International Paper plant, which is now closed, also contributed to the infamous Terre Haute smell.

There is still some residual air pollution from the company near Route 63 and Margaret Avenue which coats railroad ties with a petroleum derivative. Contrary to what has been said in the media, the TH sewage plant has never been a significant source of air pollution in city neighborhoods.