Engineering considerations in favour of this setup: The cost of that 30% oil loss is less than engineering/site selection of a system that can be fully drained

Engineering considerations in favour of this setup: The cost of that 30% oil loss is less than engineering/site selection of a system that can be fully drained. The cost of a more robust system that isn't as damaged by use is higher over it's lifetime assuming the *Emergency* use case than just creating/prospecting replacement damageable reserves if necessary. If someone wanted a small reserve for 'market stabilizing' short term and repetitive small fill/drains they could build it for a lower cost than making the emergency reserve resilient enough to serve this purpose. Can't claim these are true in this case but also remember that norms were much more enforced at this time and voter could be expected to punish bad politicians (This was a couple of years after watergate) so expecting political parties to hold short sited/corrupt politicians to account when they were doing something visible may have influenced what they expected to happen to a "get me reelected on lower gas prices damn the consequences politician". So the main concern could easily be the stated 1 or 2 emergency drawdowns in the next century and we'll over engineer it so it can handle 5.