This action will address the agency’s residual risk and technology review (RTR) of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Primary Magnesium Refining source category. This action will implement the residual risk review requirements of section 112(f)(2) of the Clean Air Act (CAA) and the technology review requirements of CAA section 112(d)(6). The current Primary Magnesium Refining NESHAP was promulgated pursuant to CAA section 112(d) on October 10, 2003. The NESHAP establishes emission limitations, work practice standards, and operation and maintenance requirements based on maximum achievable control technology (MACT) for controlling emissions of hazardous air pollutants (HAP) from the source category. The HAP emitted from this source category include, but are not limited to, hydrochloric acid, chlorine, dioxins and metal HAP. Pursuant to a court order (Community In-Power and Development Association, Inc. et al v. Pruitt, No. 1:16-cv-1074-KBJ (D.D.C. 2018)), the EPA must complete the final action for the Primary Magnesium Refining NESHAP by July 31, 2026.