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Old 09-09-2011, 02:42 PM   #1
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Ground water coming up through slab...will sump pump help


My basement is 30' x 30'. In some locations water is coming in where the wall meets the floor, and is some locations water is coming in through the concrete slab. I'm thinking about having an interior french drain put in to take care of the water that comes in where the wall meets the floor. Since the interior french drain will lead to a sump pump, and since the sump pump will sit in a pit that is deeper than the slab, is it reasonable to expect that ground water will reach the pit first and be pumped out before it comes up through the slab? Would I have a better shot at this outcome if I had more than one sump pump installed? Thanks in advance.

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Old 09-09-2011, 04:25 PM   #2
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Ground water coming up through slab...will sump pump help


The mechanics of a perimeter drain (it is actually a perimeter drain, not a French drain, but the history is too long to recount here) is very simple. The perimeter drain is installed below the level of the floor, typically six inches or more below floor level. The perimeter drain runs around the entire basement, either inside (an interior perimeter drain) or outside (an exterior perimeter drain).

The drain collects groundwater, and the collected water flows to the sump pit, which can be anywhere along the drain. The sump pit is typically at least 14 inches deep, and the perimeter pipes drain into it. The pump comes on when the water level in the pit rises to within approximately six inches of floor level. The exact on and off settings for the pump are controlled by the float.

The water from the sump is pumped out, generally to the storm drain system, but if there is no storm drain system, the water can be pumped to a low spot far from the house, so the water does not flow back into the sump pit (that is called short cycling).

You do not need two pumps, one is fine, and you only need one sump pit. The critical issue is that the perimeter drain needs to be properly installed. There are numerous threads on this site discussing proper design and installation methods for perimeter drains, do a search and see what you find.

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Old 09-09-2011, 04:40 PM   #3
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Ground water coming up through slab...will sump pump help


Thanks, Daniel. I get how the perimeter drain handles the water that's coming in from the cove joints. But I also have a few spots towards the center of the basement where water is coming up through the slab. It seems to me (and I could definately be wrong) that the perimeter drain won't handle this water. Is this the case, or am I not understanding correctly? If this is a limitation of the perimeter drain, will the water that's coming up in the middle of the slab reach the sunken sump pit before it get's to the slab and be handled this way; or would this only work if the pit were located right by where the water is coming through the slab?
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Old 09-09-2011, 06:18 PM   #4
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Ground water coming up through slab...will sump pump help


The perimeter drain will handle all the water around your house, including any groundwater under the slab, provided the basement slab is constructed on clean gravel or sand. I have a sump pit in my house, and I don't even have a perimeter drain, simply about a foot of gravel fill under the slab, and the pit collects water from the entire basement area, no problem. Perimeter drains are much better at collecting water, so unless your slab is on poorly draining soil, you should have no issues, assuming the perimeter drain is correctly installed.
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Old 09-09-2011, 09:53 PM   #5
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Ground water coming up through slab...will sump pump help


So long as you don't have a source of water, such as an artesian well or a flowing underground stream, directly under the house, the perimeter drain will stop the seepage of water up through the middle of the basement floor.

Depending on the porosity of the soil directly under the house, it may take several days of operation of the sump pump with perimeter drain before the middle of the floor dries up.
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