Overflow hole

[CanuckPool]

The builder installed one of those overflow holes in the deck of my pool.

16x34 IG vinyl with a stamped deck.

2 questions, what exactly does it do, I pull the lid off and the water is about 2 feet from the top. and second, should I be draining it or let it be.

The pool is now closed and I was just wondering.

Oh, yea, I am in southern ontario and it can get pretty cold here for long periods of time.

[matt4x4]

I'm not 100% sure what you mean by "overflow hole", but I think you might be talking about the sump access hole, which is there so you can pump off the groundwater that collects under your pool causing hydrostatic pressure under your pool which continually wants to push your pool up trying to pop it out of the ground.
If the water in the sump is 2 feet from the top, you better pump that down soon, that's a whole lot of pressure working against keeping your pool an inground.
Verify first that this is what the access hole is for, but I'm relatively sure about that, once you get it pumped down, it will likely fill pretty quick again if there's that much water in there right now, so keep pumping it off until the level stays a little lower (like 4-5 feet down minimum).
Do you have a high water table where you are???

[CanuckPool]

I am not sure what the water table is at. The PB mentioned that it is soemthing what you described, to collect water that accumlates around the sides and I guess under the pool, sort of like a safety device I guess. He said the water should drainout naturally but it really hasnt moved since the end of summer. I will take the shop vac to it and take it down another foot or two. The PB said that not too many other builders put this on their pools, I guess its just an extra extra.

what about winter, I guess the water in there just freezes.

[sevver]

The water table does not freeze, and your pumping it down will just be a waste of time. I would guess that the purpose of it is in the offchance that you would have to drain your pool, you would want to drop a pump in there and get the water down so the pool does not float.

And in case you ever do have to pump the water down, you need to pump for as long as it takes to get the water to slow down coming into the pit, which would be better known as a "well-point".