This action addresses the agency's residual risk and technology review (RTR) of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Hydrochloric Acid Production. The Hydrochloric Acid Production NESHAP, subpart NNNNN, was promulgated pursuant to section 112(d) of the Clean Air Act (CAA) on April 17, 2003. The NESHAP established emission limitations and/or work practice requirements based on maximum achievable control technology (MACT) for controlling emissions of hazardous air pollutants (HAP) from process vents, storage tanks, transfer operations, and equipment leaks. The HAP emitted from these sources include hydrochloric acid and chlorine. This action implements the residual risk review requirements of CAA section 112(f)(2) and the technology review requirements of CAA section 112(d)(6). CAA 112(f)(2) directs EPA to revise the NESHAP if such revisions are required to provide an ample margin of safety to protect public health or to prevent, taking relevant factors into account, an adverse environmental effect. CAA section 112(d)(6) requires the EPA to review and revise the MACT standards as necessary, taking into account developments in practices, processes and control technologies, no less often than every 8 years. The RTR proposal was published on February 4, 2019 (84 FR 1570). The proposal included findings that the existing standards provide an ample margin of safety and no developments were identified in our technology review. Therefore, no changes to the standards were proposed based on the RTR analyses. The proposal added electronic reporting and removed exemptions for periods of startup, shutdown and malfunction. The final rule adopted all of the proposed decisions and changes as well as a provision for maintenance vents for which the agency sought public comments. The final rule created a small cost savings for regulated entities. Pursuant to a court order (California Communities Against Toxics v. Pruitt, Case No: 1:15-cv-00512 (D.D.C.)), the EPA was obligated to complete this action by March 13, 2020.