It's the closest thing we have to an earthquake, and it's all taken place in your back yard. You can't dig a six foot hole and be surprised to hit water. We have high water tables in marshy areas, clay and hard- pan layers that hold rainwater close to the surface in hilly areas and artesian wells, water forced to surface in the oddest places. Any pool contractor worth his salt has provided for the water table in every pool he's ever built. Think of the ground as a sponge.
Water exerts a steady downward pressure.
Anything invested in saturated soil receives lift. This is your'well- point'. Remove the plug and you'll find a 3' thick bed of small rock that lies under the entire deep- end of the pool. The rock bed acts as a collection basin, encouraging the free flow of ground water. The plug is removed with a plug wrench, a simple tool any friendly pool store would be glad to loan.