asbamba,
It could be failure of the hydrostatic valve in the bottom of the pool, if there is one.

Thank you!!!! I have just spent the last hour googling Hydrostatic Valve. Our problem may not be as bad as I think.

I'm glad you told me about this because now my concern is the pool walls caving in. What a physics lesson the last hour has been.

I am going to call our local pool install company this morning and get their opinion.

Then I'm going to call my local building inspector and see what they know about ground water in my area. I'm not hoping for much though because we are small town rural.

But I appreciate this answer very much! I'm hoping we can get this done now.

We are also going out to the garage and poke around. We have 3 valves. Two go to the skimmers and we were told to always turn them off in the winter after blowing them out. Now I understand why we were told to never turn off the bottom drain.

Thank you. I believe you too are correct in your assumptions.

Since I wrote this morning I visited a local pool company that installs in-ground pools. I was heartened to learn because this pool has poured concrete walls that I'm a bit better off than if it was not poured concrete. (I don't know what else it would be if not cement poured into forms).

I'm told that although the ground water is still a problem; it may not be as bad as I initially thought due to the strength of the poured concrete.

The pool installer did tell me that before I jumped to conclusions about the hydrostatic valve, I need to get into the pool and move the fallen cover from the bottom to be certain there is not a large tear in the liner on the floor of the deep end.

The pool installer then gave me the name of another pool installer and told me that this is a delicate job and he would not undertake it; but this other man has tackled things like this before.

Please keep your comments coming. We are very appreciative and not nearly as despondent as we were when it happened.

UPDATE - Here is what we know today in this continuing saga. The following paragraph was lifted from a physics web site:

"If the bottom of the pool is below the level of ground-water, and the pool is empty, the pool would want to float in the underground water. The deep end of a pool can actually rise out of the ground by as much as18" when the pool is emptied for repairs.

If the water were to be removed with a high water table in the surrounding ground then the pool may float up out of the ground like a barge. You then have a big problem on your hands. The hydrostatic relief valve will open allowing the ground water to enter the pool to keep the equilibrium and to relieve built up pressure from underneath the pool. If there is no water in the pool, the hydrostatic valve can not help you."

Consequently we really don't have the luxury of waiting until spring to repair this. What we have now for certain is a new cover, a new liner and water. What we still don't know is if the lag bolts drilled into the cement are still intact or if they were "ripped" out of the cement when the cover went down. If that is the case, all new cement will need to be poured. Keep your fingers crossed for me and think positive thoughts as this would most likely be a huge expense.

With that said; our insurance adjuster tells us most of this will be covered under our homeowners policy. (The 7 year old liner will be depreciated.) When our policy was written the pool was not listed as "an exclusion". Thank you to our local insurance agent.

We have a pool person coming over next week to assess the situation. This is a man that pool companies recommend in these situations because that is all he does, tackles pool situations no one else will touch. He indicated to us on the phone that if there is no tear in the bottom of the lining he would ideally like to get some water in this pool up to the frost line to mitigate the chances of the cement walls from caving in. His analogy is that what we have here is basically the foundation of a house without the structure on it.

More as we know it......please feel free to discuss as at this point we feel we need all the information we can get.

Thank you.

There are a lot of scary images online of pools that have "floated" and they freak me out! However, let me just say ... whichever way the water left your pool (mysteriously), it seems reasonable to assume groundwater could get into the pool the same way, equalizing the pressure and keeping it from popping or floating the pool immediately. That said, I wouldn't want to wait to get things fixed, just for my own peace of mind.

My concrete pool (not vinyl lined, this is a gunite pool) is currently empty and being remodeled. The builder came out and dropped a pump into the pool and drained all 35,000 gallons of water out, then drilled a few weep holes in the deep end bottom (we do not have a hydrostatic valve in our main drain) which keeps the shell stable - ground water can come in or out at will. Now, I wouldn't want to leave my pool like this indefinitely, but it's been like that since before Thanksgiving as our remodel drags on with weather delays.

If your hydrostatic valve is faulty in some way (perhaps clogged with leaves) and opened to allow the pool water out, but somehow closed and now won't allow groundwater in, that should be addressed asap.

There are a few other very active pool forums that might have more active members to give lots of advice. One is called trouble free pool and you can find it with google easily.

I also found this link about the valve malfunctioning, thought it was interesting.

Here is a link that might be useful: stuck HRV

Mia:

Thank you for that link! I understand.....there may not be a problem at all. If there is a hole in the liner and there is ground water it will come in the pool and equalize on its own. If there is no hole in the liner and the valve is open; water will come in and equalize on its own.

I attached a photo of what the pool looks like today. Hard to believe but since this happened on February 14, we have had many many more inches of snow and then it warmed up so we had rain and a melt that I've not seen this early in a long time. Today it is 44 degrees. Unheard of here in the Springfield, MA area in mid-February. Consequently we now have a frozen block of ice on the bottom. And now that is blocking water from coming in or out as it is on top of the cover that fell in too. Ugh!

I still have the pool expert coming to look things over next week. Most likely with that block of ice he will not be able to determine anything............

I'll keep you posted.

Are there photos anywhere on the forum where I can look at your pool? Just curious.

Thank you!

Good luck - keep us posted. I hope everything is OK (as ok as it can be when the pool drained, anyway!)

That reminds me I need to update my renovation story anyway ... here's my current thread.

Here is a link that might be useful: OKC reno

Update for anyone still reading this thread:

The pool guru that we found came here yesterday to look around. He determined in his professional opinion that he can fix everything and that due to the fact that I'm in an area surrounded by companies that are gravel banks; I have a pretty close to zero chance of having a ground water problem that will cave in the sides of the pool.

Whew! That was really good to hear.

The plan of attack is this; order the liner and the cover now. As soon as he can get a couple of 65 degree days he will tackle this. He thinks mid to late April.

What we have decided to do is to take the deep end hopper and fill it in from 10 feet deep to 5 or 5 1/2 feet deep. We do not have a diving board. This is because with less water; we will be able to keep it warmer in our limited swimming season. (Memorial Day to Labor Day). We are also going with a better quality American made 28mil vinyl liner. The pool guru is fairly certain that the 7 year old liner has a hole in it and that we don't have a hydrostatic valve problem. He thinks it is a Brazilian made liner and not 100% vinyl, but some sort of hybrid. I can't wait until we can remove that block of ice from the bottom and find out if he is correct.

Comments are welcome if anyone has any ideas.

More as it happens.

April 8, 2014

All is good. We had a much longer winter than normal....our mid to late April fix turned out to be mid to late May.

When the liner came out we discovered what saved us was the original pool was poured cement. Like having an 18 x 36 house foundation without a house on it. The pool installer said there was little chance that the outside ground water would have caved the pool in.

Since our pool season is so short and our water has always been too cold; we decided to fill in the hopper half way. We turned a 10 foot deep end into a 6 foot deep end with the water line at 5 and 1/2 feet. What we hope to accomplish is less water; warmer water. We also chose a much darker blue color in the hopes that will hold the heat too.

In the end; we never found out why the water drained out. The insurance adjuster sent an engineer who claimed he found a dime sized hole and he's certain that's where the water all drained out. I'm skeptical because if that is true then there should still have been water BELOW the hole. There was no water. I also don't think we even had a hydrostatic valve either. The bottom drain that was removed has no evidence of any moving parts. And of course the insurance payment will be a pittance after all, but that's for another forum I'm sure.

Attached are all the photos. If any questions don't hesitate to ask.

April 17, 2014

May 1, 2014 - the deep end before filling it in.

May 6, 2014 - Filling it in.

May 20, 2014 - Took longer than expected as we had MUCH rain this year.

May 30, 2014 - Ready for water.

May 30, 2014 - Liner installation. Above photo should have said "ready for liner"

June 1, 2014 - They actually put the water in on Sunday!

June 1, 2014 - Ready to Swim

June 1, 2014

One minor problem........it was such a rainy season that the bobcat sunk lower than anyone imagined.....now we need a landscaper. LOL, the least of our problems.

One more factoid.......you may notice that the bottom of the pool now has 2 bottom drains instead of the usual 1 drain. Here in Massachusetts we had some unusual mishaps with children being held underwater on the bottom drains. In an effort to mitigate, the state passed a law that now 2 bottom drains are required as each of them has less suction than 1 drain would have.

Our first pool was a vinyl liner too. One Spring, we opened it and found it empty. There was a hockey puck size hole in the deep end through the vermiculite. No idea what caused it. Had it patched and a new liner put in, and never had another problem.

As a pool professional of over 35 years, IN NEW ENGLAND, this is something I have actually seen several times. My first thought was multiple pinholes in the liner due to a stonedust bottom, which is very common, second was possibility of ants/termite damage on the bottom if the bottom was done with sand ( also very common )-neither of these seem to be the case here. Third would be the possibility that the main drain cover may have failed, possibly jarred loose when vacuuming the pool,and the gasket has separated and therefore not really visible as a tear or leak ( I would lean on this as the cause more than anything else. )

There would be no hydrostatic valve in this vinyl pool, rarely if ever used in vinyl installations. The dual main drain is the new code NATIONWIDE, and any renovation or new install requires these dual drains.

Either way, looks like you got it repaired and hopefully you'll have another 12-15 years with this liner.