"Alan" wrote

There used to be an oil tank in the ground here that was abandoned
because of leaking and was only 8 years old at the time. Some others
nearby lasted over 20 years. Knowing the hassle and expense they have
caused for removal and decontamination, I would never put one
underground even if it were allowed and would never buy a house with
one in the ground.

We have some customers that have ones that are over 50 years old. Out of all
of the (major) problems we have had with tank leaks, only one was an
underground tank. If someone asks to have one removed, we charge $400. That
includes removal, disposal, and labor. There are still a lot of people
having them put in the ground. I think it's because people don't want an
ugly tank sitting beside their house. I usually suggest that they put some
lattice work around it and plant bushes.

It is totally legal to put them in the ground (for residential
applications), but I am starting to lean towards advising NOT to do it just
because of the hassles when selling the house. I've talked to a lot of the
local real estate companies in my area and they are starting to tell
prospective buyers that having an in-ground tank is a liability.