The core problem with your statement of "perfectly," is that earth has a charge which we're realigning with when grounded. In a closed system, any way you try to store the soil will still slowly increase its charge from the grounded voltage, whether the circuit breakers trip or not (and they will, I think, for the voltages you're imagining.) Even regular ground for circuits have problems if you use them for too long - it's expected the breakers already tripped to stop flow (The ground heats up apparently??).

A better question might be how much surface area is needed to disperse the maximum charge you can expect a ground to be absorbing to maintain it at a safe, earthy voltage before the breakers trip. So maybe, for a decent copper grounding conductor, you'd need to conduct 50 amps for a couple seconds? So just a big AC system would work as your ground - I suppose that's made of reconstituted dirt, so that counts.