As discussed in the “How to avoid your pool turning into a boat” post, the project requires a great deal of drainage:

There are many drainage aspects to this project.: A plethora of drainage locations Long drain behind the upper retaining wall to prevent water placing pressure behind the wall. Trench drain on top of that wall for surface water. Trench drain on the pool deck for splash water and rain. Subsurface drain for edge landscaping. Drainage for flower bed. Drain beneath pool to prevent hydrostatic pressure. We’re addressing this last one today.