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Old 02-07-2008, 06:25 AM   #1
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Foundation drain and sump pump

I am working on a friends house who has a finished basement. The house is 18 years old and has poured concrete foundation. The current drainage system which has worked until now has been a gravity drain. Recently the "exit" pipe collapsed and the basement flooded creating alot of damage. The gravity drain system is hooked to a pit 18" diameter x 2 foot wide. We are trying to decide whether to fix the collapsed pipe and/or install an additional system(i.e. sump pump) to prevent future problems. Roto-rooter has told us they could not install a sump pump to code because they cannot drill through the concrete foundation. As a temporary measure we installed a sump pump in the pit with a hose out the window to stop further flooding for now. I would like to better understand the drain pipes attached to the pit & their route and function. All the pipes are about 10" below the floor surface. There are two black pipes and one white pvc pipes. Are the black pipes the drains that are collecting water from the perimeter of the foundation? And is the white pipe the exit drain? I am mostly confused because water rushes into the pit from the white pipe(but not so much the black) when the sump pump brings the water level down. From back up, possibly? More importantly, I want to make sure I have placed the pump at an optimal depth. Before we installed the pump the water level was close to the top of the pit(big rain storm). The manufacturers recommendation for the pit size for this pump was 18"diameter by 10" depth. Since the existing pit is 2 ft. deep, I put two patio blocks under the pump to raise it up some. My question is, should I raise it up further to match the manufacturer's recommendation or is my situation different because I am working with an existing gravity drain system? Lastly, when water overflows in a system like this, where is it actually getting in the building? Does the back up of the drainage system cause the water level to rise & it seeps in between the foundation wall and floor? If anyone has any advice I would really appreciate it. My apologies for the lengthy explaination. Also, if anyone has any recommendations for books about foundation structures and their drainage systems that would be helpful too. Thanks so much.


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Old 02-08-2008, 11:32 AM   #2
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Seriously consider finding the routing of, and repairing, the gravity drain.

The theory of a sump pump is to eject water faster than the water comes in from other places such as ground seepage.

When the outlet hose goes up and out a window or something like that, some water will alwasy fall back into the pit when the sump pump cycles off.

I don't know where your white pipe and black pipes go but the typical perimeter foundation drain gradually collects water seeping within the ground. Below a certain underground level (the water table which varies from location to location) any open space such as a non-watertight basement or a perimeter drain pipe will collect seepage. The perimeter pipes are below foundation level and are near or at the perimeter so they will collect seepage before the basement does. There should then be a pit of still lower elevation where all these pipes come together. The pit needs to be big enough taht enough water will collect slowly enough that a sump pump can cycle on and off with several minutes before it comes back on.

Alternatively, if there is lower ground some distance from the house where one pipe can exit the pit and slope downhill and emerge (your gravity drain), then no sump pump is needed. If your gravity drain has collapsed some distance from the house, the part leading up to the pit can collect water (if it is not watertight) and contribute to the water in the pit as opposed to take water out of the pit.

The sump pump should be as far down in the pit as possible but if the pump is not submerge-able (submersible) it must be high enough so that if power fails and the pit overflows, the pump motor won't get wet. Depending on the model of pump, this limitation may make it impossible to completely empty a deep pit.

Yes, the backup makes the water level rise. If the pit is not emptied, the entire drainage system will fill up and your basement starts to receive seepage next, either through an imperfect joint between ffoundation wall and basement floor, or because a pit right in the basement overflowed.

>>> Roto-Rooter cannot install a sump pump to code.
Because they (are unwilling to?) (are not capable of?) (are not permitted to?) drill a hole in the foundation? By the way, an additional hole drilled in the foundation needs to be properly sealed as it would otherwise be an additional entry for ground water seepage.


Last edited by AllanJ; 02-08-2008 at 11:55 AM.
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Old 02-08-2008, 10:35 PM   #3
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gravity drain is always best, since basements often flood when the power is out. having a backup system (the sump pump) is a good idea though.
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Old 02-10-2008, 09:36 AM   #4
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Thanks for taking the time to explain all this. It was really helpful. This site and all the good advice has been my best find in awhile. Thanks again!
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