First spring. High water table. When to pump?

[SirNoSplashing]

Hello all, this is my first spring as a pool owner. We have a high water table every spring, my two sumps in the basement run non stop for around 3 months, then they are dry the remainder of the year. We have 100% sandy soil conditions for what its worth. Right now the water table is about 3-4' lower than the water level in the pool (that is to say, the water table is about 5' from the top of my decking). If it matters, the pool is about 7' in the deep end and tapers up quickly from there. So really only the deep end is surrounded by water right now. The pool is fully wrapped with concrete decking. I have read online that pools popping out is pretty rare and only really a concern if you are draining the pool. My pool installer suggested to pump in the spring, though I think this was CYA on his part.
Is there a general rule on when buoyancy becomes a concern? I assume the largest driver would be the water table height relative to the water height in the pool. More upward pressure the closer these get.
Thanks!

 

[Newdude]

Is there a general rule on when buoyancy becomes a concern?

When you drain below the water table. For every inch past that level you have less of a pool and more of a boat.

why are you draining ?

 

[SirNoSplashing]

When you drain below the water table. For every inch past that level you have less of a pool and more of a boat.

why are you draining ?

Appreciate your response. To be clear, I am not draining. I am basically asking under what circumstances do you need to pump around the pool. In other words, should I be concerned at all if my water table is 3' from the water level in the pool? 2', 1' ? At what point should people care about pumping water around the pool (assume pool is full)?

 

[Newdude]

At what point should people care about pumping water around the pool (assume pool is full)

Gotcha. 'Dewatering'. IIRC it's fine if the pool is full but some fiberglass pools definitely have drains/pumps installed for this exact reason, with the spring being a likely time of use.

I see it as spitting in the ocean. Your basement is an example where my brain goes with this. You aren't getting rid of the ground water, you are only temporarily getting it out of your basement faster than it's coming in. Without that defined space of 'the basement' under the pool, you are pumping a nearly unlimited supply of ground water with a sump pump.


Let's ask 2 of our fiberglass people for their thoughts.

@Texas Splash
@YippeeSkippy

 

[Texas Splash]

With the pool 100% full, pop-out may not be an issue, but depending on the base material used, that may be something to consider. If they used gravel, less of a concern. But if they used sand, you wouldn't want that disturbed by flooding from below. Does your pool have a main drain? If so, a hydrostatic valve was probably installed for equalization purposes as well. You seem to be a bit skeptical about the installer's comment to install a pump, perhaps rightfully so. But you might consider checking with other installers and/or pool owners in the area. See if you can get a consensus for your local area.

 

[SirNoSplashing]

With the pool 100% full, pop-out may not be an issue, but depending on the base material used, that may be something to consider. If they used gravel, less of a concern. But if they used sand, you wouldn't want that disturbed by flooding from below. Does your pool have a main drain? If so, a hydrostatic valve was probably installed for equalization purposes as well. You seem to be a bit skeptical about the installer's comment to install a pump, perhaps rightfully so. But you might consider checking with other installers and/or pool owners in the area. See if you can get a consensus for your local area.

Thanks for this. They backfilled with small gravel all around and "massaged" it in as they went. They backfilled at the same rate they were filling with water so the two levels went up together.
I believe I have a main drain? There are two suction ports near the bottom of the sidewall in the deepend. At the pump I can have it draw from these, the skimmer, or both. These came pre-installed from Latham. Are those what you call a main drain?

 

[YippeeSkippy]

You don't mention if you have a dry well point near your pool? My builder put on in, with a skimmer lid on it. We can open the lid and inspect to monitor water under the pool. Never had any, so never had to pump it out.
Your pool water is acting as the weight to hold your fiberglass "boat" down. Never, ever, ever drain the pool... I wouldn't even feel too comfortable with any builder doing it unless they're fully insured against floating my pool?

Maddie

 

[SirNoSplashing]

You don't mention if you have a dry well point near your pool? My builder put on in, with a skimmer lid on it. We can open the lid and inspect to monitor water under the pool. Never had any, so never had to pump it out.
Your pool water is acting as the weight to hold your fiberglass "boat" down. Never, ever, ever drain the pool... I wouldn't even feel too comfortable with any builder doing it unless they're fully insured against floating my pool?

Maddie

Yes we have a 12" pipe out near the deep end, and yes finished off with a skimmer lid. The opening is barely large enough for a pump, but it fits. Since I have a high water table I always have spare sump pumps around. Before they poured the concrete I actually ran conduit and 1-1/2" PVC underground so I could fully hide the pump while running it, if I wanted to. Right now there is no pump installed in the pit, but its ready for it. My other issue, is that I have nowhere to pump it to. So I find it almost pointless to pump the massive "pond" that is our water table, because its going maybe 40' away and sinking right back into the sand. I guess the point is to relieve the hydrostatic pressure, though I am not even sure how effective that would be. As @Newdude said its an unlimited supply of water down there.

I never intend to drain the pool. Its still not clear to me if there is ever a point where I need to pump the water table around it. I am leaning toward no based on the comments. If the hydrostatic pressure is ever enough to overcome the weight of the filled pool + my concrete, then I don't see a scenario where my sump pump stands a chance at making a meaningful impact.

 

[Texas Splash]

There are two suction ports near the bottom of the sidewall in the deepend.

Those serve as deep end drain type functions but may not have a hydrostatic valve. I typically think of HSVs in floor drains to protect from upwards pressure underneath, but you can ask your installer to confirm. With a gravel base/backfill and full pool, you should be in good shape. I understand your concern about the in ability to pump water from the pit more than 40' away (if needed), but if you had days/weeks of heavy rain, it may help that localized area. A little insurance perhaps?

 

[Newdude]

As @Newdude said its an unlimited supply of water down there.

It might very well help in a flash flood situation where 6 inches (?) fell in short time and you could suck it out as fast as it was draining past the pool. Your pool would also be full at that time so they'd likely cancel each other out, but I do love anything that increases your odds, even by a little bit.

We had floods here a while back when the water table was unusually high and a wet spring showed up. I watched several friends and neighbors pump their basements for a couple weeks and they never made any headway, they were just removing it from the basement faster than it was entering. It'd get dumped in the yard/street and shortly increase the same ground water table that they were trying to lower. Basically the only purpose it served was circulating it so the basement water didn't get stagnant.

 

[Mdragger88]

My pool installer suggested to pump in the spring, though I think this was CYA on his part.

I’m not quite understanding what you mean? Do you have high cya?

 

[YippeeSkippy]

<pssssst... he means "cover your tooshie", not CYA stabilizer>

 

[Mdragger88]

<pssssst... he means "cover your tooshie", not CYA stabilizer>