Civil3D users notice that sometimes they can delete a surface by right clicking it’s name in the Prospector tab of the Toolspace, and sometimes they can’t (here’s one reason at least).
If a surface has no dependencies you can do just that (right click, delete). However if other objects depend on the surface the option won’t appear. For example with a single surface and no dependencies, you can delete the surface. If you add a second surface and a volume surface, the option disappears (because the surface has dependencies).
Perhaps it would be better if the right click menu showed the Delete option, but showed it grayed out !!