The OP is probably better off to get the tank removed kinda DIY.

If the tank was pumped out originally little oil should remain.

Plus if some had leaked natural soil bugs eat oil....

chances are very good theres no big hazard,.

get a smaller machine, remove tanks, clean, cut up and sell the scrap.

remove any contaminated soil. fill hole plant grass and forget about
it.

you can do what you want, till you put the home on the market.

once the for sale sign goes up theres a million rules and costs to
deal with.