On November 6, 2020, the Environmental Protection Agency (EPA) published a notice of proposed rulemaking to approve redesignation of the Salt Lake City, Utah and Provo, Utah nonattainment areas (NAAs) to attainment for the 2006 24-hour fine particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5 microns (PM<INF>2.5</INF>) National Ambient Air Quality Standard (NAAQS), and also acted on multiple related State Implementation Plan (SIP) submissions. We also proposed to approve SIP revisions submitted by the State of Utah on January 19, 2017; April 19, 2018; February 4 and 15, 2019; and January 13, May 21, and July 21, 2020. These SIP submissions include revisions to Utah Administrative Code (UAC) Sections R307-110, R307-200, and R307-300 Series; revisions to Utah SIP Sections X.B and E; revisions to Utah SIP Sections IX.H.11, 12, and 13; best available control measures/best available control technologies (BACM/BACT) PM<INF>2.5</INF> determinations for Salt Lake City and Provo; maintenance plans for the Salt Lake City and Provo areas for PM<INF>2.5</INF>; and the request for redesignation under the 2006 24- hour PM<INF>2.5</INF> standard. Additionally, the EPA proposed to approve, through parallel processing, a request to remove startup and shutdown emission limits for Kennecott's Power Plant in the Utah SIP and the accompanying R307-110-17 revisions (draft dated October 9, 2020). Due to an administrative error, two supporting documents were left out of the docket during the initial comment period from November 6, 2020 to December 7, 2020. Thus, the EPA is providing an additional 30 days for public comment on these two supporting documents. In this document, we are not requesting comments on any other part of the November 6, 2020 notice of proposed rulemaking. The EPA is taking this action pursuant to the Clean Air Act (CAA or the Act).