[3] A second coal unit was planned, but was cancelled in 1980 after estimates for electric use in the next decade were revised showing demand stagnating.

The SCR was installed to comply with the Clean Air Act's 1990 amendments and Ohio's NOx State Implementation Plan (SIP).

[5] Flue-gas desulfurization (FGD) equipment, designed by the Chiyoda Corporation, was installed at Killen in 2007 to reduce sulfur dioxide (SO2) emissions.

Stuart Station due to economic and environmental challenges in an agreement with the Sierra Club and several unnamed parties.

[18] The lands owned by DP&L for Killen Station contain two archaeological sites that date back to the Adena and Fort Ancient cultures.