Drilling Holes in Sump Pit 1

[murpht3]

Hi,

Several people have told me to help drain the foundation better to drill holes in the sump pit. The problem that I am having is water is apparently coming up in the middle of the floor of my basement (through the tiles). Our house sits on an exceptionally high water table (for the area at least). The basement is equipped with a french drain that empties into the sump pit. My question is, what is the point in drilling holes in the sump pit? It is to make it more porous? How much of an effect does this have if the foundation is solid all the way through? What size holes would be effective? How many? I apologize if this is a simple and / or dumb question. My background is in electrical engineering...I figured somebody here might be able to help. I am sick of getting water in my basement!

 

[SteveBausch]

Personally, I think the suggestion comes from people who are unsure of the concept.

Sump pumps are in sumps because thats the lowest point in the floor. If making the floor porous would eliminate the water, you wouldn't need a pump.

The pump exists to export the water away from the building. Perhaps using sewer line, most likely away from the location. To a certain extent, sump pumps are a game of pumping the water away faster than it can re-enter the water table and seep up again in the basement. Something of a joke that can sometimes mask the problem.

 

[murpht3]

I understand what the sump pump is doing...the reason why I ask is because I have heard several (qualified) people tell me that this is a good suggestion. I do not claim to be an expert on cement dynamics, but I can see where having a smooth cement surface (i.e., the smooth, flat, square sump) would prevent water from escaping the cement easily. I am looking for a way to help displace this water, if it's causing my problem. I have some water which enters through the walls (which I am sure is because of poor drainage and/or leaks around the foundation outside). But I am trying to prevent the water from coming up in the middle of the floor. I find this strange since the water level in the sump is lower than the floor. I wonder if it could be traveling under the tiles from the walls?

 

[RDK]

It sounds like there is inadequate drainage under the floor. This simply means that the water is coming into the area faster than the drain and sump system can take it away.

There should be a gravel layer under your basement floor. The water should be able to flow freely through this layer into the sump where you can pump it away.

If this layer is too thin, not porous enough or has become blocked with fine material, then drilling holes in the sump will do nothing. The water is not getting to the pit fast enough. The fix for this involves removing part of the floor and installing new drains or excavating outside the building and installing new perimeter weeping tiles. Neither is an economical undertaking especially if the basement is finished.

If the problem is that the water is not getting from the under slab drain into the sump pit it self fast enough then drilling holes will allow the water to get to the sump and be pumped away. This is an economical fix.

What is happening where the drains enter the sump? Are they flowing full? If they are then the water is getting to the sump, just not getting into the sump. If the drains are only trickling into the sump then the water is not getting to the sump and you have the expensive problem.

Of course, you should get some advice from a local qualified geotechnical engineer since the problem may be more involved than this. If there is an exceptionally high water table and a fast recharge (the water is flowing into the area through a porous soil) then there may not be anything that you can do about it anyway.

Personally I’d drill some holes and see if the water enters the sump faster and drops the local water table below the basement floor. Observe proper safety precautions because you will be using an electric drill in a potentially wet location. A GFI on the power supply is the minimum.

You should also make sure that the roof downspouts are directed away from the house and that there is good positive drainage away from the house. Use extensions or splash pads if necessary. The roof is one of the biggest causes of water in the basement. You essentially have a big funnel putting all the rainwater in one location.

Often in newer houses the backfill from the excavation settles and creates a local negative drainage towards the house, which will serve as a recharge area for the local water table. Even decorative flowerbed edging can trap water next to the house and prevent it from flowing away. It doesn’t take much slope, just enough so that you can see that the ground drops off away from the house.


Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[cvg]

It is not traveling under the tiles, from the walls - but is a result of your extremely high water table in the area.

Your drainage system is inadequate to capture the water and convey it to the sump.

drilling holes will not likely help, since you said that "the french drain empties into the sump pit". However, I agree that drilling them won't hurt and is cheap.

As described by Rick, the water flows into the french drain and then into the pit. Drilling the holes might allow a small amount of water to come directly through the sump pit, but will not affect the capacity or the function of the french drain.

Does your sump ever overflow? Do you have standing water in the basement? If not, then your sump and pump are working fine, and the subdrainage system (the french drain and gravel layer) is inadequate.

 

[murpht3]

There are already two large diameter (about 1.5 inch) holes that are on two sides of the sump which I can see have gravel in them (so I assumed that these went to the other side of the slab. It is my belief that the french drain drains (which follows the perimeter of the basement wall where the water problem is the worst) through these holes as well...but I have no way of visualizing if this is the case (the water might just sit there to evaporate for all I know). The sump never overflows, but the pump certainly runs much more than all of my neighbors - even on very dry days. I am the second house from the bottom of a dead end hill with a brook that runs perpendicular to the street at the end. The house up the hill from me (about 10 feet from my property line) has a ground level that is higher than mine (vertically) and pitches downward towards my property.


My house is kind of stuck in a "tub" if you will. I have considered setting the level at which the pump comes on more aggressively (i.e., lower) but the one time I did do that it operated at about an 80% duty cycle. I was concerned that I would never get that level as low as I would like. So after a few very dry days, I waited for the level to rise in the pit then set the level about 1/2 inch below that.


So I know that ground water is definitely a problem for my house. I know for a fact that two outside gutters are not properly draining (e.g., one needs to have a new PVC pipe laid to the street). But I am trying to chizel away at this problem piece by piece. I have upgraded the sump pump, installed a dehumidifier (attempt to keep the basement humidity at 70%--it will rise to 84% without it running), etc.

 

[Focht3]

Are the french drain's discharge points below water at all? In general, you should keep the water level in the sump below the invert (bottom) of your french drain's discharge points in the sump. Otherwise, you will have water backed up the french drains, reducing their effectiveness.

How old is your home? How long have you owned it? How much do you know about the design and construction of the home?

Regarding the suggestion to drill holes in the sides of the sump pit: it may or may not be a good idea. In general, I don't like doing things like that. But it is possible that it could help relieve the water pressure somewhat. The key to this question lies with the original construction details - which we don't have.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[murpht3]

Yeah, the house is at least 35 years old...I have very little details about the construction of the home. I am assuming that the french drain was added after the house was built since it does not span throughout the entire basement (it's only at the front of the house in the basement where water comes in). I have the water level set below those two holes in the sump.

 

[RDK]

If I understand you, you had lowered the cut in level for your pump and then were concerned because it was running too much?

While it was running it was taking away the water that you are concerned about. I’d reset it to the lowest possible cut out level and let it run forever if necessary. (just don’t let it run dry.)

How long was it running at 80%?

Around here we have some of the flattest land in the world. (You can sit on your front step and watch your dog run away from home for 3 days.) It is an old glacial lake bottom and we live near a former river delta. The result is that we have a very porous sand and a water table about 8-15 ‘ below grade (it varies considerable depending on general moisture levels time of year and believe it or not wind direction.)

When we install sewer and water lines the area is typically dewatered by placing several sand points along a line. I have seen areas where it requires two lines with points 8’ on center and 48 hours continuous running time to dewater a trench enough to allow safe excavation. The discharge can be a 6” line flowing full.

My point is that that’s a lot of water. You with your one pump, and a small French drain that is most likely silted up somewhat after 35 years, might have to run the pump almost continuously during the wet parts of the year.

Do you have a check valve installed on the discharge line? If not then the water in the discharge line could be flowing back into the sump and causing the pump to start and stop quickly without actually pumping any significant amount of water.


Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[murpht3]

I get what you are saying. How thick is the slab in a basement typically? I am guessing that this is just moisture moving its way up through the floor rather than the water level since I have the level in the sump set below the floor. I will try lowering the turn on level some more and see how it does. It ran for about 24 hours like that.

I made sure to install a check valve with this newest installation of the sump pump. The last owner didn't have one and I remember he used to wonder why the pump never moved any water from the sump (the pump has to push the water about 10 ft. vertically to where it drains into a pipe outside).

I wanted to avoid having this pump run near continuously for obvious reasons--to save energy, prevent premature failure, etc. But I will lower the turn on level some more and see the results.

 

[PWS]

I have no engineering degrees and less construction experience but I am a homeowner with similar problems.
If your objective is a dryer basement with little if any water on the basment floor, then your sump pump and it's capacity has to be able to remove the water at a higher rate than the supply. If at times you're actually removing water from the water table the capacity may require (two) or more pumps operating in tandem. The pumps must be expendable to maintain the dry basement. Purchasing sump pumps may have to become a necessary maintenance item if they are required to run 24/7. Remember that the cost of replacing sump pumps is small compared to damage of personal property, heating and air conditioning equipment, or even health issues from high humidity and/or mold.
Runoff from roof, rain gutters, and landscaping are conditions you can control usually without costing too much money.
The "pipe" your sump discharges to hopefully connects to some municipal storm sewer and does NOT return the water to the water table.
Phil