"No legal case here."

True enough, except that this is the USA. A good legal position is not required, as we have a jury system, i.e. one which in especially in politicized civic cases works on cheap moronic sentiment and envy. And in this matter, both are in limitless supply.

"tanks...at the temperature of the surrounding ground."

I very seriously doubt it. The ground is often an excellent insulator, and there will be a void space of some sort between the tank and the 'secondary containment.' So I doubt that gas delivered to a modern high-volume station that sells it out in a day or two would ever reach "cave temperature". However, I haven't stuck any thermometers down into tanks, so I will await the "investigation" to tell us at ludicrous expense.

The real point is that any difference will rarely exceed a couple of cents, and the posted price will adjust to compensate, leaving little effect on the 'consumer'. But the cosseted monopolists - the lawyers and the manufacturers of massively overpriced "certified" equipment - will laugh all the way to the bank.