Vapor barrier positioning for piece over EPS geofoam when filling an indoor concrete pool

I’m transforming an unused indoor concrete pool into functional flooring area and would appreciate assistance on vapor barrier positioning before installing geofoam.

A picture of the swimming pool area is connected. The hot tub in the far left corner will be destroyed and filled to floor grade.

The pool is approximately 35 ′ × 15 ′, with a typical depth around 4– 5 feet (7 feet deep end/ 3 ft shallow end). The entire swimming pool space is 48 ′ × 24 ′.

The strategy is to fill the swimming pool with EPS geofoam blocks (likely EPS19) and after that put a 4 ″ reinforced concrete slab over the whole space, including both the existing flagstone floor and the former swimming pool area, so the finished slab is constant.

The pool has been empty for about 10 years, and the concrete shell seems in good condition.

One installer suggested the following assembly:

1. Line the pool shell (walls and bottom) with vapor barrier

2. Set up the geofoam obstructs

3. Install another vapor barrier over the geofoam

4. Pour the strengthened slab

My understanding is that the vital vapor barrier is the one directly under the slab, primarily to control vapor transmission into the piece and any future flooring.

Typical geofoam details I’ve seen look more like:

Concrete swimming pool shell
→ EPS geofoam obstructs
→ 10– 15 mil vapor barrier
→ enhanced concrete slab

So my concerns are:

1. Exists a building-science benefit to lining the swimming pool shell with a vapor barrier before placing the geofoam, or is this typically unnecessary?

2. Could a liner under the foam potentially trap moisture against the concrete shell, or develop a slip layer under the blocks?

3. Because the piece will extend across the entire room, would it be more suitable to set up one continuous vapor barrier throughout the complete flooring area prior to the put, rather than only over the geofoam area?

4. I’ve likewise seen some discussions about drilling drainage holes in the bottom of the pool shell before filling. In a case like this (indoor pool, empty for ~ 10 years, shell appears sound), exists any advantage to doing that, or is it normally unnecessary and/or might produce other problems?

The completed space will be utilized as a home theater and health club, so loads are property but somewhat heavier in the gym location.

Any insight into best practices for this type of project would be greatly valued.

Thank you.