Back in the Atomic Age, the Marshall Islands served as America’s nuclear playground, because you can only explode so much in your own backyard before there ain’t no backyard left to explode. In all, the Pacific Proving Ground hosted 67 nuclear blasts, which produced at least 110,000 cubic yards of lethal nuclear debris, as well as soil which could only be considered fertile if the crop you’re raising is Fallout bosses. Thankfully, the U.S. disposed of all that in a safe and conscientious manner.
Nope, we just left it right there on Enewetak Atoll, though we did have the common decency to cover it up with something that looks like a football stadium, as is the American way. The massive concrete cap is known as the Runit Dome, though the slightly irradiated locals more accurately refer to it as the Tomb.
This was only a stopgap measure, of course, meant to keep the problem out of sight and mind until a more permanent solution could be settled upon. The more permanent solution settled upon was “not caring anymore,” so we left.