Thinking out of the box here guys so slap be if this is out of line.
I'm not sure how important it is to you, but you should be able to relocate the existing contactor to the pump house and set a 220 sub panel down there. You could run low voltage control cable to the pump house to control the sprinkler pump and areator (if desired) in lieu of running air line from the house. The materials wouldn't be too expensive for this and you have 500' of hose or cable to bury either way. But you would have power at the pond availible all the time.
