I've got a legendary with the plasma effect, have been avoiding energy weapons completely until now but this is a ballistic weapon with extra plasma damage.

I noticed it makes green goo piles like a plasma weapon, so I stopped using it just in case, don't want the landscape or especially my settlements permanently marred with green puddles.

I just know it's been an issue in Bethesda games before so I figured I'd check.

I believe it will eventually go away, although I not completely sure, other than I turned a BOS soldier in a power armor suit into glowing red ashes with my cell rifle, to have it respawn as a full BOS power suit in it place quite a few days later... though it could of been a bug.

I have seen ash and goo piles remain after area respawn.
Such are simply activators which are now linked to nothing.

A timer script on the ash pile or goo pile was very useful in Skyrim to make them self nuke.

I think they go away in the wild but not in settlements as setlements never respawns and it looks like they lack the function who removes killed enemies.

I've noticed some disappear if you kill an enemy that respawns. For example, one of the named feral ghouls (like Mrs. Summers or something) I remember turning into goo and the goo pile sat there for the longest time, only for the feral to spawn elsewhere and the goo pile finally disappeared. Same for the two synths that sit outside of Malden Center. Turned them to goo piles, they respawned, goo piles disappeared.

But then I've seen some remain there for the entirety of the game for no apparent reason. So in the end, who the hell knows why they do what they do, and why it remains unfixed after so many years. Well done, Bethesda.

What about mole hills? I still have infront of my Red Rocket shop. Have no way to get rid of them. Xbox One. Almost makes me want to start a new game lol.