Leak deep underground, your basic pool nightmare

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
Hi Rich,

Thanks for the replies.

I think maybe I've stabilized at the leak level. The loss of water has slowed to maybe 1" a day now. Is that just evaporation? I don't know but it ran fast to about 4.7' of water below coping and has slowed. After several days, I'm at 5.1' below coping. That's a tough depth to dig.

I disconnected my suction piping today at the pump and tried to use my endoscopic camera down and was reminded that it does a big z relatively shallow. That limits my ability to camera it. I'll try again with an electrician's fish.

I did camera my skimmer basket drop pipe (runs 10' down to the main drain pipe, not my first choice for design). It looks intact and the water level is more or less the same as the pool (as you'd expect).

I can't see or reach the relief valve but I did some palpating with a pole and didn't feel anything amiss. I guess I'll pump it dry, inspect the hydrostatic relief valve, and I don't know...

Thinking out loud here. I need to know where the leak is and there are 4 possibilities:
1. skimmer drop pipe
2. main drain lateral
3. suction side pipe after skimmer joins the main drain lateral
4. hydrostatic relief valve
5. shell

Correlated inspection options:
1. Skimmer pipe: Loosely inspected with a camera already
2. Main drain lateral: Not likely as it is at 10' depth. Can loosely inspect this with a camera if the pool is empty - I inspected it last year
3. Suction piping: I probably would need to expose (modest dig, possibly some outer edge shell jacking) the top lateral to drop a camera down this pipe.
4. HRV: Can physically inspect if empty, could cap and refill
5. Shell: can inspect if the pool is empty. I don't really suspect the shell.

Solutions:
1. Deep dig
2. Very deep dig
3. Deep dig
4. Cap
5. Depends on the size.

Digging is unfortunately a headache due to space constraints and equipment access. The trees don't help either.

It seems like draining, capping the HRV, and refilling is a good next step. I can inspect and camera some stuff.

I'm assuming it can't be on the pressure side as my returns are very high in the pool.

I sure wish I had 2" piping and sweep elbows everywhere. It's hard to camera 1.5" standard 90s.
 

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
I agree, I'm definitely a little hrmm about the continued drop but it was losing water closer to 4" a day at first. It's a little strange to me that it slowed steeply and suddenly (ie no reason to believe the leak is greater above).

Last year when the HRV failed it ran hard ~4" a day until had <1' left.

I'm probably busy for the week in terms of outdoor work so I'll be giving it a few more days to stop.

I could wait for it to finish entirely if I had/could buy some kind of pond type circulator pump to throw in. It's not reasonable at this point to jury rig the pump and filter (unless someone has a suggestion for how to do that reasonably) and it is taking long enough to drain that the remaining water is getting unreasonably funky.
 

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado

Using this calculator which doesn't include climate (mine is dry and reasonably hot) suggest 300g per day to evaporation normally and perhaps 150g given the reduced surface area at this point. Very approximately 1" loss in my pool is maybe 500 g. So I guess you are correct. Only 1/3 of my loss is to evaporation. I'll let it keep leaking awhile longer and see what happens.

I wonder: if I have a long vertically split pipe underground in the suction line (~50 yo pvc), would the leak slow linearly once it reached the vertical split? Or perhaps slow non-linearly due to the lack of head above the crack? I can't imagine that a leak at the main drain or HRV would see head related leak slowing while still having 4'+ of water above those fittings. Either way, it seems like that idea is suggestive of a leak ~5' underground?
 

Bperry

Gold Supporter
Aug 20, 2020
1,071
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60

Using this calculator which doesn't include climate (mine is dry and reasonably hot) suggest 300g per day to evaporation normally and perhaps 150g given the reduced surface area at this point. Very approximately 1" loss in my pool is maybe 500 g. So I guess you are correct. Only 1/3 of my loss is to evaporation. I'll let it keep leaking awhile longer and see what happens.

I wonder: if I have a long vertically split pipe underground in the suction line (~50 yo pvc), would the leak slow linearly once it reached the vertical split? Or perhaps slow non-linearly due to the lack of head above the crack? I can't imagine that a leak at the main drain or HRV would see head related leak slowing while still having 4'+ of water above those fittings. Either way, it seems like that idea is suggestive of a leak ~5' underground?
Interesting idea, it’s possible I suppose. But everything I’ve read as well as a leak detection company that came out to mine say underground pip leaks are extremely rare. The guy said it’s usually the skimmers joint unless there’s an obvious hole in the wall. Exhaust all other options before digging stuff up.
 

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
Interesting opinion by the leak guy.

But not too relevant to my case as the the water level is way below the skimmer (3.5' or so) and the skimmer pipe drops straight down 10' so I can use a cheap amazon endoscopic camera to look for a big break. My little camera isn't good enough to really inspect the pipe in fine detail.

But yes, digging is terrible so I'm hoping to avoid any digging.
 

Bperry

Gold Supporter
Aug 20, 2020
1,071
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
Interesting opinion by the leak guy.

But not too relevant to my case as the the water level is way below the skimmer (3.5' or so) and the skimmer pipe drops straight down 10' so I can use a cheap amazon endoscopic camera to look for a big break. My little camera isn't good enough to really inspect the pipe in fine detail.

But yes, digging is terrible so I'm hoping to avoid any digging.
Equipment pad is dry? I might try checking pipes near there with a little digging if possible. Seems strange to have a pipe just break so far underground. Unless the hydrostatic valve is bad, which would be my first likely suspect to check.
 

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
Bperry,

Thanks for discussing this problem with me. I'm definitely pulling my hair out a bit.

I can't run my equipment once the skimmer is dry so I haven't run the equipment in at least 10 days. The water went way below the skimmer fast and hard, much like my hrv failure last year caused.

But unlike last year, the leak has slowed dramatically now that I'm ~5' below the pool coping. At this point, it can only be the slope and deep end pool shell, main drain body, the hrv, the lateral main drain, the skimmer drop pipe, or the combined suction side plumbing. Everything else is high and dry.

One reason I think a broken pipe under ground isn't impossible is that I had a tree break the underground conduit and electrical line last year (don't know which tree) and now I'm having a tree near the pool removed tomorrow. It's definitely not out of the question that a tree root could have someone damaged the underground pvc. Presumably if I could get a camera into that location, I would see the damage. Unfortunately because my plumbing is narrow, tight elbowed, and has excessive directional changes, I can't get the camera there without digging. If I do dig, I'll definitely upgrade any exposed pipe to 2" and sweep elbows.
 

doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
Well, the leak stablized. I still can't be sure it isn't the HRV as I did shock and brush the other day and could have reseated the HRV if that was the problem.

At this point, I think the lower shell and the main drain and its lateral are innocent. HRV can be dynamic so it might have changed. Suction line could still be cracked. Shell could still be cracked.

I'm going to run it just the main drain this weekend. If I truly have a cracked suction line, I expect I'll lose water pretty quickly but it can be hard to gauge backflush loss vs leaking. If I don't lose much water, I'll blame the HRV.

My other idea is pump it dry, maybe pressure wash it, and then just cap the HRV port and fill to above the current leak line and see what happens. If the shell is cracked, I assume I'll visualize it after pumping. If it takes water to the current 5' below the coping and then can't fill, I have my answer. If it takes water but then loses it rapidly back to the 5' level, I have my answer. If it fill entirely, I'll blame (correctly I hope) the HRV.

The other option is to dig to get a camera in the suction line and look for a break.
 

Bperry

Gold Supporter
Aug 20, 2020
1,071
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
Well, the leak stablized. I still can't be sure it isn't the HRV as I did shock and brush the other day and could have reseated the HRV if that was the problem.

At this point, I think the lower shell and the main drain and its lateral are innocent. HRV can be dynamic so it might have changed. Suction line could still be cracked. Shell could still be cracked.

I'm going to run it just the main drain this weekend. If I truly have a cracked suction line, I expect I'll lose water pretty quickly but it can be hard to gauge backflush loss vs leaking. If I don't lose much water, I'll blame the HRV.

My other idea is pump it dry, maybe pressure wash it, and then just cap the HRV port and fill to above the current leak line and see what happens. If the shell is cracked, I assume I'll visualize it after pumping. If it takes water to the current 5' below the coping and then can't fill, I have my answer. If it takes water but then loses it rapidly back to the 5' level, I have my answer. If it fill entirely, I'll blame (correctly I hope) the HRV.

The other option is to dig to get a camera in the suction line and look for a break.
How many gallons in the pool, it must be a decent amount if its 10' depth. That much water draining that fast would be worrisome for the surrounding soil.
 

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doggonepool

Gold Supporter
Jul 22, 2020
29
Front Range, Colorado
Barry,

That's a good point, for other people with leaks. But I think not important for me.

I suppose it is possible for the gunnite layer to be compromised by a leak but I have cobble and sand ancient river bed under my property. It drains well and is stable. Last year, when I put a camera in the HRV, it was not very deep and had a nice layer of cobble under it and that was after losing all of the water. Someone sitting on sand or with a vinyl liner over sand might have a problem but I'm not too worried.
 
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