The Environmental Protection Agency (EPA) is approving Washington State Implementation Plan (SIP) revisions to the Southwest Clean Air Agency (SWCAA) air quality regulations submitted by the State of Washington, through the Department of Ecology (Ecology) on June 22, 2023. The revisions were submitted in part to respond to the EPA's June 12, 2015 "SIP call" in which the EPA found a provision in the Washington SIP applicable in the area regulated by SWCAA to be substantially inadequate, providing affirmative defenses that operate to limit the jurisdiction of the Federal court in an enforcement action related to excess emissions during startup, shutdown, and malfunction (SSM) events. The EPA's approval of the SIP revisions to the substantially inadequate provision corrects the SWCAA deficiency identified in the 2015 SSM SIP call and the EPA's January 2022 finding of failure to submit. Washington withdrew some portions of the revisions submitted that were not identified in the 2015 SSM SIP call and therefore the EPA is not approving those withdrawn portions. The EPA proposed to approve this action on December 10, 2024, and received no comments.