Kennecott Copper Corporation (KCC) operates a mine at Ray, Arizona and a concentrator and smelter at Hayden, Arizona. An inspection to acquire data with which to evaluate the operation of existing process and particulate matter air pollution control equipment at the smelter was conducted by EPA personnel on January 28, 1976. Substantial amounts of process and control equipment information was requested of, and received from, Kennecott. The following conclusions are based on the inspection and a review of the information obtained. 1. The Ray Mines Division smelter is one of the two Arizona smelters which has a fluo-solids roaster. It is also the only conventional smelter, excluding Inspiration, which demonstrates compliance with the process weight regulation. 2. This smelter is the only Arizona smelter which has discontinued returning converter slag to the reverberatory furnace and has made a concerted effort to seal all holes and leaks in the reverberatory furnace to minimize infiltration air. This practice reduces the gas volume which must be handled by the air pollution control system.