The Superfund program was created in 1980 and actually has a much more complex name: the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). All the most toxic sites in the country were basically put on a list, and hopes were high that somehow, some way, sometime - they'd get 'cleaned up'.
Missoula is certainly not the only Montana city that has struggled with homelessness issues, but its Reserve St. bridge problems have been some of the most well-known.