Does a Sump Pit with drain tile system also need small holes near bottom of pit?

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Old 02-28-14, 10:54 AM
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Does a Sump Pit with drain tile system also need small holes near bottom of pit?

Looking for a yes or no here.

A plumber told me those holes were likely for installation to get the drum down into some water.
 
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Old 02-28-14, 05:45 PM
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That question could be answered yes or no.

My answer is yes.... because in my opinion you want any water that is under the slab to drain into the pit regardless of its origin.
 
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Old 02-28-14, 06:40 PM
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Thank you, PJ. I appreciate your answer.

If you knew that water would still rise and enter the basin in the opening for the 4" drain tile tube, would it change your answer? Remember that I have a deep pour basement.

Thanks.
 
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Old 02-28-14, 07:15 PM
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I guess it would depend on the water table. If the level was consistently high then there would be no way to lower it.
 
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Old 02-28-14, 07:29 PM
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The buoyant force upward of the water can make a sump hard to hold down until you can anchor it. Draining a few holes will allow the pressure to equalize. A couple for small holes are not a problem and possibly a benefit in the long term. - You are working with/against a water level in the soil that is not like dealing with free-flowing water out of a gutter.

I installed interior drain tile in my old basement and we knocked a big hole in the floor to dig the dirt out and had to get one guy to stand in the sump while we put two long 2x4's and a few sandbags on them to allow us to fill around the sump and then pour concrete around it and hold the sump down. We used a mixture of concrete sand and 3/4" rock to fill the excavation to 4" below the top of the slab and top side of the sump. We also put a few long lag screws through the top side of the sump so they projected out far enough to be in the new slab repair concrete.

Installation of a big plastic tub below water and keeping it the and steady for a while takes more force that most people think. A 15 gallon sump will take well over 120 pounds weight to barely keep it down if the soil is wet.

Dick
 
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Old 02-28-14, 08:04 PM
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PJ, thanks. I am not looking to lower the water table - I'm looking to stop my pump from working when really it doesn't need to be if the water table isn't rising and just sitting below my foundation.

I believe the water table often sits somewhere between the bottom of the basin and the opening for the 4" drain tile tube. If the two small holes weren't there, it would not fill my basin and ask my pump to run.
 
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Old 02-28-14, 08:21 PM
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Thanks, Concretemasonry. I appreciate your reply.

My basin is in. A plumber suggested that the holes were possibly drilled by the contractor/installer to do exactly what you were talking about - allow the basin to be lowered into the hole with water present so that they could secure it and secure it with concrete.

I'm now wanting to plug the holes and stop unnecessary pump operation by constantly having to drain water that wouldn't otherwise be entering the basin. If the water level were to rise up it would enter the basin in the opening just under the 4" drain tile tube.

Would you plug those two small holes near the bottom of the basin?
 
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Old 03-02-14, 05:50 AM
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Come to think of it, if the sump pump float(s) is correctly adjusted, it doesn't make any difference whether there are holes in the bottom of the drum/tub/line. The pump should come on only after the water has reached the level of the bottoms of the incoming drain pipes.

(Using trial and error you may get away with the pump turn on yet higher to further reduce pump starts and stops and without having the far corner of the basement flooding.)

If water came up through the holes then the pump won't (shouldn't) start running until the water gets high enough to enter via the drain pipes anyway.

Water coming up through the holes left open in the bottom will not cause the water level to go higher than the next lowest hole(s) under where the drain pipes enter compared with sealing off the holes in the bottom.
 

Last edited by AllanJ; 03-02-14 at 08:00 AM.
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Old 03-03-14, 05:45 PM
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Thanks, AllanJ ~

I am hoping to plug the holes and stop pumping out the water-table water that is below a 9' basement (deep pour) floor. If I had an 8' basement, my guess is no water would be coming through the holes and my pump would rest more than it does now. Unless water rises to the level of my drain tile tube opening, I don't know why I need to keep pumping water out that's always there.
 
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Old 03-03-14, 06:59 PM
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A good drain tile installation does not (is not meant to) respond immediately to melt or rain storm. A good drain tile installation works 24/7 to lower the general water table under and around your home. It also creates a greater capacity of the soil to temporarily hold the water from a real problem and not have the hydrostatic pressure blow in a wall or have a floor with cracks act like a spring for short term events.

Pumping out some excess is not bad since good sump pumps are made for severe service because of the importance. Just make sure you get the water way and not allow it be re-absorbed and pumped out again.

It sounds like your installation is OK, but does not give you much insurance for a big one.

Dick
 
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Old 03-04-14, 07:58 PM
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>>> I don't know why I need to keep pumping water out that's always there.

You don't need to.

If the water comes up into the pit and stops about halfway up to the drain tubes then it can stay that way.

Simply adjust the pump floats so the pump doesn't come on until the water level gets up higher, to the drain tubes.
 
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Old 03-05-14, 05:26 AM
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With the bottom of the pit liner/basket sealed, considerable upward force due to buoyancy is imposed when the water table is high. Depending on how the pit liner was installed, it could float up out of the ground, deforming other components in the system.

Come to think of it, if the water comes up through the bottom holes into the pit and levels off below the drain tubes and stays that way with the pump breaker off, usually nothing useful is accomplished repeatedly pumping it out back down to the bottom of the pit. Under those circumstances the water table is at about where the water leveled off. (But don't leave the pump breaker off all week long; a rainstorm or snow thaw/melt could cause the water table to rise and flood the basement if you are not attentive.)

The level an inch or two under the drain tubes entering the pit is a magic number. This is the level of the bottom of the gravel cushion on which the drain tubes sit all around the basement perimeter.

Normal operation of the sump pump causes the water table under the perimeter drain tubes to be artificially lowered to approximately this magic level, all around the house. However 3 to 4 feet outside, away from the drain tubes, the water table is back at the natural water table which, if that is above the basement floor level, is why you have the sump pump system in the first place. (Except in a few cases involving underground springs, the entire area enclosed by the perimeter drain pipes, namely the middle of the basement, also has its water table artificiailly lowered.)

But if the natural water table is below the magic level but above the pit bottom, it is not threateneing your basement. If you keep emptying out the pit anyway, the water table at the pit is artificially lowered to about the pit bottom. But 3 to 4 feet from the pit the water table is back at its natural level or the magic level whichever is lower. Because you are not lowering the water table below the magic level all the way around the house, it is just a waste of electricity to set the pump turn on float below the magic level. (When the pump does start, it should empty out the pit almost completely although not so meticulously so as to stir up dirt.)

If the soil under your basement floor slab is extremely porous, such as being gravel at least 3/16 inch, the 3 to 4 feet mentined above might be somewhat greater and might even make it unnecessary to have drain tubes around the perimeter. Also the water table could vary noticeably even over a horizontal distance of just a few feet even in the absence of a sump pump and perimeter drain system. So there may still be some trial and error needed to set the sump pump floats to keep the far corner of the basement from flooding.
 

Last edited by AllanJ; 03-05-14 at 05:56 AM.
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Old 03-05-14, 08:17 AM
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TJ,

Just set your shut off on your pump to the level that the water table comes up to. As long as it is below your inverts of the tile coming into the sump you are still getting sufficient drainage under your slab.
 
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Old 03-05-14, 10:44 AM
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Thanks for responding with the good insights.

To make matters more interesting, my main pump is a Zoeller M98. I'm told, and I'm trying to confirm, that this is a pump in which the float cannot be adjusted and to adjust it I need to raise the pump up on a brick or something like that. True?
 
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Old 03-05-14, 11:30 AM
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tjhouse44 -

Don't worry about the details.

Some people just want to collect and get rid of water. Others want a system that is long term for structural and other water problems.

Perforated sumps (without drain tile) with decent fill (coarse sand and rock) around have be used successfully for years as a means for long term water control. They can eliminate the use of interior drain tile, but are not as effective unless you have enough at proper locations.

There is nothing wrong with raising the pump or control height to control the amount of time the pump runs, but the amount of long term protection from short term protection is not as good.

Dick
 
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