The copper ore was heated in the smelter until it melted and the liquid copper could be separated from the other minerals. The leftover molten material cooled to form a brittle solid slag that included harmful metals such as arsenic and lead. The rocky slag was dumped along the Commencement Bay shoreline, covering sandy beaches to depths of 30 feet, and into deeper waters to create a 23-acre breakwater peninsula. Asarco estimates that 15 million tons of slag are on the site. However, the slag can be broken by waves and storms, creating new surfaces where water can slowly dissolve the harmful metals.
Metals released from the slag can poison marine plants and animals.
The site is being cleaned up under the federal Superfund program. Part of EPA's selected remedy for the site includes armoring the shoreline to prevent further loss of slag material into the bay. NOAA worked with EPA and Asarco to build a habitat component into the shoreline cleanup plan to accelerate coastal habitat recovery. The photographs below were provided by the Washington Department of Natural Resources and show the smelter before the stack was removed. The nearby slag peninsula forms a breakwater that protects a small boat basin.