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Anonymous Poster

Sealing a Tank for Potable Water

10/08/2008 1:02 PM

I had installed to our well a 2700 gallon cement tank turns out it is a septic tank with the fins or ribs inside cut out. After installation tank leaked with about 25 inches of water in it. Had someone come out to seal the many cracks and it still leaks. Any ideas? Is it because it is a septic system? It really is basically a large cement tank.

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#1

Re: Sealing a Tank for Potable Water

10/08/2008 2:37 PM

Is the tank buried ? Or above ground ? If the tank is buried dig at the center of each side and try to find the leak. Once you locate the discharge area of the leak repairing it should be easy with some water proofing materails.

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Anonymous Poster
#8
In reply to #1

Re: Sealing a Tank for Potable Water

10/09/2008 7:28 AM

he already fixed the leaks.

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#2

Re: Sealing a Tank for Potable Water

10/08/2008 4:25 PM

You say it has been patched already with less than desirable results: Had someone come out to seal the many cracks and it still leaks.

Why then would you attempt to keep chasing your leaks? I would look at either installing a liner on the inside of the tank, or replacing it alltogether with something that will perform over the long run.

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#3
In reply to #2

Re: Sealing a Tank for Potable Water

10/08/2008 6:30 PM

I saw one set on a big rock and it cracked the bottom when it was filled with water. They were using it as a holding tank to water cattle.

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#4
In reply to #2

Re: Sealing a Tank for Potable Water

10/08/2008 7:01 PM

Gee, didn't anyone tell you that concrete is porous and you can't just patch, you have to seal the whole tank? The fact is, I use to paint the insides of septic tanks for a living.

Although I was painting them for septic and grease trap purposes, I have some friends who painted water towers who said they used the same coal tare epoxy coating material as I did.

My friends said that if you saw what was inside water towers, you wouldn't want to drink the water from them. And I'm not one to say to use cold tar epoxy either, but I can assure you that it's probably the cheapest coating to use for such a thing.

However, I've also coated various other kinds of tanks and I happen to know of the leader in supplying such coatings.The name to look up would be Tnemec

http://tnemec.com

PS: don't let their engineers/salesman get you going overboard, because I've put $1,600.00 worth of coatings in a tank that was only going to hold road run off.
That's when coal tare would have been the better choice. $24 per gallon -_vs- $65
Another hint, an alcohol (MEK) solvent based material will adhere to a moist surface better than a Mineral based (paint thinner) solvent.
Also, you'll find that to dry out the tank, you are better off not having soil on the top of the tank, because moisture will always travel down with gravity.
And be careful: I always used an free air air supply. (The fumes can kill you, or you may wish you were dead.)
If you spray, you need to ground your pump, because one spark- Ka Boom.

Good luck and I hope they don't take you to the cleaners.

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Anonymous Poster
#5
In reply to #4

Re: Sealing a Tank for Potable Water

10/08/2008 11:39 PM

In Oz we have product called Shower Seal which is an excelent concrete sealer.

Though by the sound of it you should return the tank and buy a decent one! Plastic is good but it needs to be thick so black algae doesn't eat through it!

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#10
In reply to #4

Re: Sealing a Tank for Potable Water

10/09/2008 8:17 AM

Congratulations on being the first to:

  • Comprehend the question
  • Recognize the contradiction between sepsis & concrete...and potable.

Lacking information to the contrary (that the soil was dug out for a distance all around the tank), obviously the tank is underground...after all it's a septic tank. I can see converting such a tank for "cistern" style water storage...say, for irrigation/sprinklers. But the part about drinking from it? That's a bit harder for me to...swallow. That is to say: even if I was a far-out survivalist...no way I'd drink out an underground septic tank...

  • Unless it had impermeable resilient liner with full coverage (bottom, sides, top)
  • Because prevention of fluid intrusion from soil is just as important as prevention of leakage outward to soil;
  • Because, once the tank is full...very hard to know (other than by sickness) when contamination has entered the tank from the soil.

In answer to OP poster's question:

No, the [whatever was sealed near the tank's floor] had nothing to do with its functioning as a septic tank. (In fact, it would represent a failure of a septic tank...possibly a reason your tank was abandoned?) Outflow (actually overflow) from a septic tank to leach fields (where "processed" water is released into the soil) occurs through outlets near the top of the tank (so only surface-level "hold water," only water free of solids) is permitted to enter the drain pipes; and so that the drain lines are at a level at which there is sufficient soil above and below through which tank effluent can drain and leach into permeable soil. If the tank had been leaking near the bottom, possibly such that tank water level remained below the leach line outlets, then the tank would have ceased to function as a septic tank.

Here's something else to consider. Government Code for placement of a septic tank generally requires a certain horizontal separation from any water source...in particular a well source, but possibly even to water service entry lines. Now, the fact that your septic tank has been abandoned and will be converted to other use does not mean that the code requirements (and former approvals) are not still in force...because the leach field is still there, very close by. In your case, in fact, you are proposing to place a potable water reservoir right in the middle, to a greater or lesser degree (think of those leaks that were sealed), of the former leach field! If you do not bother to consult the code authorities for approval of your potable water tank, you could be leaving yourself open to penalties and other costly consequences.

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Anonymous Poster
#11
In reply to #4

Re: Sealing a Tank for Potable Water

10/09/2008 10:22 AM

Sunnyside,

Do you have an address that I may reply to. I have some questions that I would like to ask of you in the area of applying coal tare epoxy coating material to the inside of a metal tank.

Thank you.

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Anonymous Poster
#9
In reply to #2

Re: Sealing a Tank for Potable Water

10/09/2008 7:30 AM

No, he was just curious whether the leakage (before being sealed) had been part of the Septic effluent discharge function of the (former) septic tank.

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#6

Re: Sealing a Tank for Potable Water

10/09/2008 12:03 AM

www.kryton.com

Scroll to "About Crystalline Waterproofing"

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Anonymous Poster
#7

Re: Sealing a Tank for Potable Water

10/09/2008 6:21 AM

Seamon corp makes a geomembrane developed for drinking water

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Commentator

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#12

Re: Sealing a Tank for Potable Water

10/09/2008 11:13 AM

fyi I believe there have been some past discussions on these forums concerning various forms of underground water tanks e.g. http://cr4.globalspec.com/thread/17088 (otherwise, hope septic tank you apparently got was not "used"!! ;)

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#13

Re: Sealing a Tank for Potable Water

10/09/2008 11:28 AM

We do not have enough information to make cogent suggestions. If the tank is above ground now, and was designed for buried installation where the surrounding soil provided reinforcement, it would be dangerous to use above ground. Concrete has very little strength in tension (pressure in the tank), while it is very strong in compression (soil pressing on the outside of the tank) In order to withstand internal pressure--even hydrostatic pressure from filling with water-there must be steel reinforcement included in the concrete. Unless your tank has sufficient steel reinforcing (rebar, welded wire mesh) it will expand as you fill it, causing many small cracks to open, and soon a BIG crack results in total failure. There is a lot of energy stored in raising the water above ground level, and the sudden release of that energy by a tank failure can propel concrete debris dozens of feet. Lethal forces can develop over a large area.

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