Leaking Concrete Tank 3

One tedious, expensive way is to send in a diver with a dye wand. He can inject dye around the suspect areas and see where it moves to. There's your leak.
Too bad you didn't ask before you sprayed that gunk on. I bet they promised that it would stop your leaks easy. Where are they now? The problem is that if there's a crack, the spray on either transmits the crack or fails at it.
For individual wall cracks, you should epoxy inject. If the whole tank is bad, sheet liners are much better. You batten them to the boundaries above the water line.

that certainly sounds like a pretty big breach. never crossed this before in a tank, but an idea that might work...
we've used bentonite clay liners for pond lining on fire-water-supply ponds. when those leak, the manufacturer recommends pouring sacks of powdered bentonite (from the well driller supply store) into the pond. the bentonite seeks the leak and plugs it up. i'm not saying that would be a permanent fix for your situation, but i could imagine that it would seek the leak as well, accumulate, and even may plug... then you drain the tank slowly out the outlet and seek out the places that look like the clay accumulated. there would probably be a sweet spot where dumping more sacks would just coat the floor and obscure indications. you should check, but i would bet the gray bentonite would be compatible with your membrane and different enough in color to indicate. also, it would seem like the clay could be removed by pressure washing afterwards and not be much of a concern for the tank use.....
again, never tried it. interested in what the forum throws out there.

Yes, there are methods to detect leaks, in general. Layfield Environmental can help. They can also provide sheet liners if needed.

Liquid Rubber sounds like snake oil. A spray on polyurea liner would have been much more applicable.

If you can, just isolate all the inlets and outlets and just let the level fall over time and monitor it closely. If there are multiple leaks, which is quite likely, you should find out the elevel by monitoring the depth of water over time and watch for any sudden changes.

Hopefully you get to the point where the level doesn't fall anymore, but if not then you know it's in the floor!

what is the physical size of this thing?

with that many nozzles and outlets it's likely that the seal between the rubber liner and the nozzle face is part of the problem. Once it gets behind the there then the water will appear some distance from the problem. First make sure the nozzle fixing is good before you start anything else.

I did a fire water tank with a rubber liner and that still leaked, but at least we could concentrate on the joins and the seals with the nozzles. Once we fixed that the tank was tight.

A 20 yr old concrete tank that has been leaking that much might have a load of other issues and replacement could easily be the next best solution rather than a quick non fix like a spray on solution.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

for a rough start to determine the location of the leak I would agree with littleinch....one could also empty the tank and then start with say 1' of water and monitor the level, then do it for 2' of water, etc....how to repair I would defer to the experts in this field....

Thanks everybody for your prompt responses--it helps when we're working on the other side of the world!

Littleinch, I have enclosed the drawings of this tank--it comprises of three cells all joined together by small opening at the bottom.
JedClampett, I may have to reline the whole tank with sheets. Do you have any product recommendation?
Darthsoilguy, that is a very interesting method--may probe a little more into it.
Gumpmaster, the liquid rubber we used is:
The top view is 7'10" x 19' - 3 off

There's several good lining materials. We used to use Hypalon, but DuPont doesn't make it anymore. Currently we use HDPE or Polypropylene. But the type of liner is not nearly as important as who puts it in. I'm sure wherever you are, there's some good ones. Google them and check their references. Of course, the seams and edges are the most important. And testing them is vital.
Sealing around the openings is a nuisance. But the good news is lining is probably cheaper or about the same as you spent already.

Thanks JedClampett!

Hypalon isn't available anymore from dupont, but the generic version, CSPE (Chlorosulfinated Polyethylene) is still available. The difficulty with CSPE is in the installation and welding.

I'd recommend looking at a coated polyester such as Seaman's XR-3 or XR-5. It's much easier to install and repair than CSPE. The installation is more important than the product and most installers have a selection of products that they can offer. Focus on finding a quality installer first and then see what they recomend for products.

Are there any pipe penetrations below the water line? It wasn't clear from your drawing. If so, as others have said, that may be an important place to look at. If the leak is suspected there you may try epoxy injection at the wall pipe in addition to lining the tank.

Let's go back to basics here, at a leakage rate of over 13,000 litres a day, if this leak was above ground (I assume you have access all the way around?) you would see it. "weeping" isn't that sort of flow.

Therefore the leak is probably in the bottom 1m.

I can't work out what that weird sump thing is in the middle of the bottom chamber, but that's a good place to start.

Are there any pipes embedded in concrete? Can you get access to send a camera up them to see if these pipes are still there and not just corroded away?

Make sure it is the tank that is leaking and not the pipes or the seals around any pipe exits thought the concrete. The main concrete should be Ok unless you've had an earthquake recently, but any seals between sections might have started to perish.

you might need to excavate those particular spots to find out, but it's best to do this now than spend more money on a liner and find it still doesn't stop leaking....


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

Thanks LittleInch--very constructive advise--incidentally thats exactly how I have been trying to resolve the problem. I'll keep you guys updated on the progress.
Gumpmaster, thanks for the info on liner.

Cheers

You're welcome - sometimes we all need to know we are going about it the right way and there isn't something much easier.

Please let us know how it works out and pictures are always nice.

Have in the back pocket a cost for a brand new tank in concrete or GRP though to benchmark the costs of fixing something that is probably getting a little close to its effective life.

Good luck - fixing leaking tanks can be a never ending problem when it is not clear where it's all leaking out from....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way