Buckeye Power, Inc. and Cardinal Operating Company violated the 1.2 lb/TBtu 30-day rolling average emission limit for mercury outlined in NESHAP Subpart UUUUU and the Title V permit for the Brilliant, Ohio facility. The violation of the 30-day rolling average emission limit occurred in the Unit 3 coal boiler from December 26, 2021 to January 24, 2022. There is a concurrent ACO requiring Cardinal to operate and maintain its coal-fired boilers at all times in accordance with a newly developed mercury management plan, and to provide mercury emissions information to the EPA.