Trenching & high water table?

I am wondering how plumbers deal with standing groundwater when it comes time to backfill a rough-in underslab? I don't imagine you will wait a month for things to dry up.....

Haven't had to deal with that since I left Chicago 40 years ago. But at that time the level NEVER dropped so we just poured on top of the gravel. Had an interesting time sinking a 5' by 5' cast iron ejector basin when dealing with a water level 6" below the floor and "quicksand". Even pouring joints was an exercise in digging and bailing while a third person made the joint. Each length had to be plugged immediately.