The Environmental Protection Agency (EPA) is approving a revision to the Chattanooga portion of the Tennessee State Implementation Plan (SIP), provided by the Tennessee Department of Environment and Conservation on behalf of the Chattanooga-Hamilton County Air Pollution Control Bureau (Bureau) through a letter dated September 12, 2018. The revision makes changes to the definition of volatile organic compounds (VOC) that are consistent with changes to state and federal regulations. EPA is approving the changes because they are consistent with the Clean Air Act (CAA or Act).