Edit: Also the fact, that if the pump was at the very bottom and it failed, you'd need to have an alternative way to clear the cavern of water in order to go do

Edit: Also the fact, that if the pump was at the very bottom and it failed, you'd need to have an alternative way to clear the cavern of water in order to go down and fix the pump. Put the pump on a chain and hoist it up with a crane, like they do with pumps in lift stations.