St. Louis instrumental in development of Mississippi River hydro plant.
Metals mine and mill near Bixby, Mo., ceased operation in 1994.
Buyers and traders have been accumulating stocks ahead of the smelter closing.
Environmental group plans lawsuit if problems not addressed.
Ruling paves way for sale of plants to Dynegy. Environmental and public health groups oppose decision.
Robert Alvarez calls the West Lake a de facto radioactive waste dump.
Court said user charge was a tax and violated state's constitution.