EPA is approving a State Implementation Plan (SIP) revision submitted by the State of Tennessee, through the Tennessee Department of Environment and Conservation (TDEC) on December 13, 2012. EPA proposed action on this revision on August 16, 2013, and received no adverse comments. The SIP submittal revises the definition of "Modification" in Knox County Air Quality Management Regulation Section 13 Definitions. TDEC considers Knox County's SIP revision to be as or more stringent than the Tennessee SIP requirements. EPA is approving the Knox County SIP revision because the State has demonstrated that it is consistent with the Clean Air Act (CAA or Act).