[Code of Federal Regulations] [Title 40, Volume 26] [Revised as of July 1, 2003] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR421.20] [Page 463] TITLE 40-PROTECTION OF ENVIRONMENT CHAPTER I-ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) PART 421-NONFERROUS METALS MANUFACTURING POINT SOURCE CATEGORY--Table of Contents Subpart B-Primary Aluminum Smelting Subcategory Sec. 421.20 Applicability: description of the primary aluminum smelting subcategory. The provisions of this subpart are applicable to discharges resulting from the production of aluminum from alumina in the Hall- Heroult process.