i started using my fully modded laser rifle and ended up having a big battle around X 2 which lead to a lot of disintigrated enemies around like 10+ because of a combination of roboscorpions, lobotomites, truma suites, and night stalkers decided they were going to start spawning there (i [censored] my pants a few times there). well after that fight i went to scavange around the rest of the big empty disintigrating more enemies. well i left the big empty to off load around 100,000 caps worth of weapons in the mojave, which took a few in game weeks. i returned to scavange around X 2 again and the ash piles were gone from there, but there were still other ash piles around the rest of the big empty.
i dont know if its just that the game engine can only handle a certain amount of ash pile/goo puddles at a time and deletes old ones whenever you make more, or not. but has any one else noticed this?
edit: the mojave seems uneffected though because the ash piles fiends made in front of camp MacCarran from a long time ago were still there