"....[1988 - four years before the ConTop installation...] contamination of the soil surrounding a smelter also is of concern. Fortunately, toxic metals are present only in very small concentrations in most domestic copper ores. Only Asarco's El Paso smelter currently treats concentrates that are considered to have high levels of volatile impurities. The Anaconda-Butte and Asarco-Tacoma smelters used to treat such concentrates, but they closed in 1980 and 1985, respectively..."
U.S. Congress, Office of Technology Assessment, Copper: Technology and Competitiveness,
OTA-E-367 (Washington, DC: U.S. Government Printing Office, September 1988).
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