General requirements.

Each NSO shall require an interim level of sulfur dioxide constant controls to be operated at the smelter, unless a waiver of this requirement has been granted to the owner under subpart H of this part. Except as otherwise provided in § 57.304, the interim constant controls shall be properly operated and maintained at all times. The NSO shall require the following gas streams to be treated by interim constant controls: (a) In copper smelters, off-gases from fluidized bed roasters, flash furnaces, NORANDA reactors, electric furnaces and copper converters; (b) In lead smelters, off-gases from the front end of the sintering machine and any other sinter gases which are recirculated; (c) In zinc smelters, off-gases from mult-hearth roasters, flash roasters and fluidized bed roasters; and (d) In all primary nonferrous smelters, all other strong SO 2 streams. (e) In all primary nonferrous smelters, any other process streams which were regularly or intermittently treated by constant controls at the smelter as of August 7, 1977.