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Old 01-14-2009, 06:30 PM   #1
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Sewage extraction tank installation.

Hi there, I am in the process of installing a basement bathroom on a septic system. I have already broke though the concrete for my drain lines and installed a sewage tank about 3 feet deep. After leaving the job for a couple days, I returned to find my basin floating in the hole I dug for it. It seems that I hit the water table or there is excess water under their slab. A sump pit that is located some 30 feet away on the other side of the basement seems to be level with the water that has filled into the hole I dug for my sewage basin. The water is now about 6 inches from the top of the pit.

What is the best solution for taking care of the excess water so I can safely install my tank without worrying about it floating up through the concrete after a couple months. I should mention that the ground is hard clay. Should I install a second sump pit that is deeper the the sewage tank?

Thanks in advance


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Old 01-15-2009, 11:44 AM   #2
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I've never had to actually deal with this but here are some random thoughts:

I guess first try putting the pump and minimum water level in the sewage ejector basin and see if it still floats.

Once you pour your concrete floor around the basin (the upper part should end up embeded in the concrete) and put in the heavy pump and you get some water in it (in actual use there will always be a certain minimum amount of waste water in the bottom) it might br just fine but I understand your concern since the ground water is only 6" from the top. That would be a lot of floatation pressure.

You could add a few tapcon screws through the top flange into the concrete floor.

Most basins have some supports on the outside that go from the top flange to the body. These end up embeded in the concrete floor. You could drill some holes in these and place some bolts in to provide better grab for the concrete to resist the floatation.

Prior to pouring the slab, instead of backfilling around the basin with pea gravel to within 4" of the top, leave a deeper ring around the basin for the concrete say 12" deep and 6" wide so that you have a heavy concrete ballast weight enshrouding the basin.

Can you adjust your current sump pit float to maintain a lower water level to reduce floatation pressure?

I don't think you have to get the level below the bottom of the basin. You just need it low enough that the pump, water and concrete will resist the floatation pressure.


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Old 01-15-2009, 05:00 PM   #3
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Your electric supplier is going to love you. That pump will run around the clock, and if the power goes out the water will find its way in. I've heard they are pricey, but maybe you should give thought to what I can only call a "flush-up toilet". That would solve lots of problem down the road. As it stands now, you'd still have a job to fill that hole back in and keep it from leaking up water. Just my two cents, and I"m not a plumber.
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