Hole in the bottom of my pool - hydrostatic Pressure?

[magicalyak]

I drained the pool and took off the liner. As i was stepping on the bottom my heart sank as it went "squish". I thought the pool was above the water table (there is a stream a lot lower I thought). In any case, there is a good sized circular break popping up and a black membrance underneath (I almost broke it but I don't think I did since the water is clear).

What do I do here? Do I wait and see if the water goes down, do I sump it out or do something with that plug in the bottom of the drain? I can repair the hole with hydraulic cement I believe. I'm hoping I haven't just done something that will kill my pool. It's a 20x40 inground and the bottom is **** honestly, I'm surprised they put a liner over it in the state I found it. I'm also wondering what I do to smooth it. I haven't ordered the liner yet and figured at worst I'd pour over everything on the bottom if I had to!

Note the wetter picture, that's tonight...so I plan to look tomorrow to see if the water is rising.

Any help appreciated, I feel embarrassed to ask.

 

[swimcmp]

You have what appears to be pool base, a mix of vermiculite and Portland cement. Put a sump pump down in the bottom and keep the water that comes in pumped out. You can repair the spot that is broke up, just get a bag or two of pool krete

 

[magicalyak]

Should I unscrew the relief plug at the bottom of the drain? Seems there is some water under that "bubble". Or just wait and see if it goes down on its own.

Thanks so much for the advice

 

[swimcmp]

With the hole in pool base taking the relief valve out won't gain you anything

 

[magicalyak]

There is a membrane underneath that hole so there is water under the membrane. Going to check tonight but I'm assuming I need that to go down before I lay poolcrete right?

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[swimcmp]

Take a sharp knife and poke a hole in the membrane so the water can come thru.

 

[magicalyak]

OK just wanted to double check will do

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[magicalyak]

So the groundwater is coming up and the membrane (aka black trash bag) is ripped already. I think this break happened a while ago. If it stays wet can I just use sand there? I can't seem to get all the water out. Its only an inch or two of water though from the top of the drain.

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[JasonLion]

Yes, you can use sand. You won't be able to get a perfect match between the sand and the poolcrete, but that won't hurt the pool it will just be noticeable if anyone is walking along there. Of course given the location that seems unlikely.

 

[magicalyak]

Yeah I might end up doing that, if it was new construction I'd excavate and get a sump well under the drain but I can't afford or have time to excavate the bottom. I've noticed the leaf catcher and vacumn hit something there for last two years. I bet the last replacement covered it up. The poolcrete couldn't let enough water in so it broke.

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[swimcmp]

Personally I would never replace krete with sand. Professionally I won't use sand. I have to many customers come in after placing liners on sand with pinholes in them. Just my .02worth

 

[magicalyak]

Thanks trying to dig a dry well. Do you think one 15 ft away would help?

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[JasonLion]

It doesn't sound like you have all that much water. A dry well might well be both overkill and not enough.

You have a couple of choices. The easiest (but slowest) one is to wait until the ground water level goes down. Another is to open the post in the main drain and pump out from there while you do whatever you are going to do with the broken area. Or you can dig two or three dry wells and use sump pumps to hold the water level lower while you work on the pool.

Hundreds of thousands of pools have been built with sand under a vinyl liner. The modern approach is to use pool-crete, because it gives a smoother surface and is easier to work with when placing the liner, but there is nothing wrong with sand.