Thekevster: Who ever owns the tank is "responsible" for it. Unless condemned by the EPA, a tank is still usable. Would I buy a property with one? Probably not. A colleague has told a story of $300,000 in costs of contamination! I don't know and hope I never learn the details of that one. If you are buying and you go to your homeowners insurance and mortgage companies with the in-ground tank information, you may find that they don't want to play in your yard.
This is a matter that can be easily fixed with a removal, the cost of which is subsidized by the state to some degree, usually enough to cover the whole thing. There are firms that do this service all the time.