The Superfund program is a federal program to clean up places in the United States that have been polluted by hazardous waste. It was created by Congress in 1980 as part of the Comprehensive Environmental Response, Compensation, and Liability Act, which empowers federal agencies, including the EPA, to identify and compel the entities responsible for the pollution to pay for the cleanup.
Sites are ranked by the Hazard Ranking System from 0 to 100; if they score 28.5 or higher they're placed on the list. The first National Priorities List was published in 1983, and 263 of those sites are still on the National Priorities List (NPL). There are currently 1346 sites on the NPL.
In July 2017, the EPA's Superfund Task Force recommended streamlining the Superfund program by focusing on redevelopment potential. In a press release, the EPA announced that they "will work diligently with developers interested in reusing these and other Superfund sites; will identify potentially interested businesses and industries to keep them apprised of redevelopment opportunities; and will continue to engage with community groups in cleanup and redevelopment activities to ensure the successful redevelopment and revitalization of their communities."
The agency pulled together a list of 31 sites with "the greatest expected redevelopment and commercial potential," based at least in part on "previous outside interest" as well as "access to transportation corridors, land values, and other critical development drivers." The list is not exhaustive, according to the agency, but it is a window into the EPA's new priorities under Administrator Scott Pruitt.