That high a water table might be problematic, dd.
I designed our Family’s SU Complex w/ 1” ballast stone & 3/4” crushed bluestone, 17ft deep, 8ft wide, surrounding the entire structure, with 20 6” & 8” drainage pipes going down 20ft thru clay. It *should* withstand a flooding, but we usually don’t get enough rain to factor-in. Better to be safe than have a soggy mess, although the entire SU Complex is heavily coated and sealed and won’t ever allow moisture intrusion. I designed a dehumidifier into the heating/cooling system, but haven’t used it in 2yrs. Our wells are 300ft+ deep, so water table intrusion isn’t a problem, here.
I was wondering if those gas tanks might be the answer. I’m guessing the hardest problem would be keeping the ground water from floating it right out of the ground. I guess you could back fill around the container and hide it with heavy landscaping.
In a hurricane we can get 10-20” of rain in a day so drainage is crucial.