National Emissions Standards for Hazardous Air Pollutants: Primary Aluminum Reduction Plants

The EPA is proposing amendments to the national emissions standards for hazardous air pollutants for Primary Aluminum Reduction Plants to address the results of the residual risk and technology review that the EPA is required to conduct by the Clean Air Act. If finalized, these proposed amendments would address previously unregulated emissions (i.e., carbonyl sulfide (COS) emissions from new and existing potlines and polycyclic organic matter (POM) emissions from new and existing prebake potlines and existing pitch storage tanks); remove the vertical stud Soderberg one (VSS1) potline subcategory; reduce the MACT limits for POM emissions from horizontal stud Soderberg (HSS) and VSS2 potlines; eliminate the startup, shutdown and malfunction exemption in accordance with recent actions by the United States Court of Appeals for the District of Columbia Circuit; add provisions for facilities to avail themselves of an affirmative defense in the event of a malfunction under certain conditions; and make certain technical and editorial changes. The proposed emissions limits for POM and COS are based on maximum achievable control technology (MACT). While the proposed modifications would result in some reduction in actual emissions of POM from existing pitch storage tanks, reduce the potential emissions of POM from Soderberg potlines, and prevent increases in emissions of COS and sulfur dioxide, the health risks posed by actual emissions from this source category are currently within the acceptable range and would not be reduced appreciably by the proposed modifications.