National Emission Standards for Hazardous Air Pollutants: Primary Magnesium Refining Residual Risk and Technology Review
This proposal presents the results of the U.S. Environmental Protection Agency's (EPA's) residual risk and technology review (RTR) for the National Emission Standards for the Hazardous Air Pollutants (NESHAP) for Primary Magnesium Refining, as required under the Clean Air Act (CAA). Based on the results of the risk review, the EPA is proposing that risks from emissions of air toxics from this source category are acceptable and that after removing the exemptions for startup, shutdown, and malfunction (SSM), the NESHAP provides an ample margin of safety. Furthermore, under the technology review, we are proposing one development in technology and practices that will require continuous pH monitoring for all control devices used to meet the acid gas emission limits of this subpart. In addition, as part of the technology review, the EPA is addressing a previously unregulated source of chlorine emissions, known as the chlorine bypass stack (CBS), by proposing a maximum achievable control technology (MACT) emissions standard for chlorine emissions from this source. The EPA also is proposing amendments to the regulatory provisions related to emissions during periods of SSM, including removing exemptions for periods of SSM and adding a work practice standard for malfunction events associated with the chlorine reduction burner (CRB); all emission limits will apply at all other times. In addition, the EPA is proposing electronic reporting of performance test results and performance evaluation reports.