Pump for water under pool

A transfer pump or shallow well pump that can handle some dirty water. Getting it to prime may be a challenge and getting it pump continuously could be a challenge as well depending on how flow into the pipe is. A lower flow rate pump (500 gph or less) is probably going to be able to maintain a constant flow than a higher flow rate pump.

If you have ground water issues, install some wells around the pool that a sump pump with a float switch fits in to. This what they can run when there is water present.