CERCLA, passed by Congress in 1980, authorized EPA to create a list of polluted locations requiring a long-term response to clean up hazardous-material contamination.
[1] These locations are designated as Superfund sites, and are placed on EPA's National Priorities List (NPL).
The NPL guides the EPA in "determining which sites warrant further investigation" for environmental remediation.
In many cases the companies responsible for contamination are no longer in business, and the federal government has had to contribute to clean-up to protect citizens' health.
[2] In addition, a proposal to add the Triumph Mine Tailings Site to the NPL was made in 1993 but withdrawn in 2003 as the EPA felt that all major sources of risk had been mitigated.