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This action addresses the agency's residual risk and technology review (RTR) of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Manufacturing of Nutritional Yeast. The Manufacturing of Nutritional Yeast NESHAP, subpart CCCC, was promulgated pursuant to section 112(d) of the Clean Air Act (CAA) on 5/21/01. The NESHAP established emission limitations based on maximum achievable control technology (MACT) for controlling emission of hazardous air pollutants (HAP) from nutritional yeast fermenters. The HAP emitted from fed-batch last stage, second-to-last stage and third-to-last stage fermenters is acetaldehyde. 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). The statute directs the EPA to promulgate emission standards under CAA 112(f)(2) if such standards 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. Any such standards are to be promulgated within 8 years after promulgation of MACT standards under CAA section 112(d). 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. Pursuant to a court order, the EPA was obligated to complete the final action by 10/1/17. This final completed action published in the Federal Register on October 16, 2017, at 82 FR 48156.