The Wikipedia page makes it seem like it's been largely cleaned up for decades:
> In 1988, the NRC announced that, although it was possible to further decontaminate the Unit 2 site, the remaining radioactivity had been sufficiently contained as to pose no threat to public health and safety.
> In 1988, the NRC announced that, although it was possible to further decontaminate the Unit 2 site, the remaining radioactivity had been sufficiently contained as to pose no threat to public health and safety.
https://en.wikipedia.org/wiki/Three_Mile_Island_accident