No, plain vanilla. No tilesets either.
I'd have to check later tonight, but what I remember is that part of the map is evil and the rest is neutral (forested wilderness of some sort).
So I checked this game last night: it is an evil biome on the far left that rains blue malodorous ooze (causes blisters and vomiting). The top-middle of the map is a non-evil forested region while the middle-right of the map is a non-evil black sand area. I haven't had any evil undead show up (except for vampires, who are in their own external barracks building) so no problems there either.
The 5-6 wells are underground in black sand, located very close to my underground farms. There is a wall and a pair of doors limiting access to the wells and nothing else in there except for black sand. This area is only used for washing up since the water is stagnant.
There is no way that this was any sort of mass dumping or decontructing. #1, there is only black sand in this area (and the wells) and no stone, so there was nothing to mass dump. #2, the wells are sufficiently far from any other stone source too, since the farm is large and entirely on black sand as well. #3, the water for the wells is fed from a stagnant pond above ground, which has to pass through a fortification and a floodgate first, so there isn't any way that an enemy passed into the water supply and caused this to occur. The fortification and the floodgate are fine, only the wells deconstruct.
As I said, the wells are stagnant water and are not used for drinking - that's what booze is for. The wells are used for washing off the blue malodorous ooze and this tends to pool up around the wells quite a bit. I have no idea if this is relevant or not but thought I would throw that out there.