A few years ago I used to work for a large supermarket chain, who also sold thier own brand Gas in pumps next to thier stores.
When a gas truck crashed or rolled, the concern wasn't for the cost of the gas, it was for the cost of the cleanup operation. If the gasoline ended up in a farmers field than then entered the water table the cost rose dramatically. Compensation doesn't come cheap.
I have no knowledge of US law, but the cost of a leak will probably outweigh the benefits of storing such large quantities.
Just my 2 cents worth