[pnorman55]

Hello - we need to update our sump pump, so had a contractor come and take a look.

He noted that the water level in the sump is well about the drain tile inputs by the time the pump kicks in. When the pump triggers and the level goes below those inputs, the flow into the sump is substantial until the level goes above those inputs, and then it seems to slow down again.

But he made a claim that the water level in the drain tiles could be much higher than in the sump. That sounds like nonsense to me: when the sump is filling slowly, it's almost a hydrostatic situation, and the water level is very nearly the same throughout the system.

Also, his solution is to do ~$1100 worth of work to extend the sump pit down about 14 inches, which sounds pretty disruptive to our finished basement.

Question 1: is his claim about the higher water level in the drain tile suspect?

Question 2: Are there other solutions besides extending the sump pit? For example, changing pump on/off limits?

Many thanks,
Pat

 

[Daniel Holzman]

If you understood his claim correctly, it is nonsense. The level in the drain tiles will be essentially the same as the level in the sump pit, unless the pump is running. You are correct, the water flow is so slow that the velocity head in the water is negligible, and the levels are the same.

I am unclear from your post what the problem is that you are trying to solve. My sump pit is about 14 inches deep (relative to the basement floor), which is pretty typical. Some are a little deeper. My sump pump float is set to turn on when the water level gets to about four inches below the floor, so there is about 14 inches of water in the sump at turn on. The pump turns off when there is about 6 inches of water in the sump, so the pump drawdown is about 8 inches. This means that I allow the water level in the sump to get to within four inches of the floor before the pump turns on. This is not a problem, remember the only purpose of a sump pump is to keep the basement floor dry, so there is no point running the pump needlessly when the level is well below the floor (4 inches in my case).

Conclusion: You may not have a problem, perhaps you have an old pump, in which case replace it. I would not make the sump deeper unless there is some other problem you have not described.

 

[pnorman55]

Thanks for your response!

I'm not sure there is a real problem, except that the drain tile never completely empties. But that might be because our sump discharge drain has been poorly functioning for a while, and I think the discharge has been coming right back to the foundation. That in turn means there's not much buffer between the water level in the sump and the floor. There's a backup, but it will only trigger when the sump is almost overtopped. I think a little more margin of safety would be good, but maybe it's not needed?

I've run a temporary discharge on the surface well away from the house, so hopefully the inflow rate will drop and the drain tiles will clear.

 

[Daniel Holzman]

I still don't understand what the problem is. Drain tile is usually set well below foundation level, often 12 inches or more. So the drain tile will not drain completely unless the water table is lower than the bottom of the drain tile. If you set your float to turn on when the water level reaches four inches below the floor elevation, then during the wet part of the year the drain tile will not drain completely. This is NOT a problem.

What is a problem is that you think the sump pump does not empty to the street, a storm drain, or something similar, but instead cycles the water back to the foundation. This is incorrect, and needs to be addressed if it is the case. My drain tile does not drain completely most of the year, but the pump only turns on a few days a year, when the water table is reaches closer than four inches below the floor. Much of the rest of the year, the water table is between 14 inches below floor level and 4 inches below floor level, so there is water in the sump pit, the drain tiles are full, but there is no need to run the pump. This is NOT A PROBLEM, and if you have a similar situation, you don't have a problem either. Just make sure your pump drains correctly, test your pump monthly, and make sure your pump is adequate to keep up during heavy rainfall events.

 

[pnorman55]

Thank you for the very clear answer - I understand now that the water level per se is not a problem. Good to know.

I definitely understand that the poor discharge is a problem, and we're having that fixed.

Thanks again!

 

[Ghostmaker]

712.3.4 Maximum effluent level.

The effluent level control shall be adjusted and maintained to at all times prevent the effluent in the sump from rising to within 2 inches (51 mm) of the invert of the gravity drain inlet into the sump.

 

[pnorman55]

So, in everyday language.... the pump should kick in when the water rises to within 2 inches of the drain tile input to the sump?

By the way, I see that your quote is from the International Plumbing Code chapter on Sanitary Drainage. Does that apply to a non-sanitary sump?

Thanks.

 

[Daniel Holzman]

You have a storm drain pump, not a sewage pump. I see no relevance of a quote on sewage pumps.

 

[AllanJ]

For best performance of the drain tile, there must be an air pocket all the way around the route of the drain tile. Exactly how much the drain tile end can be submerged without eliminating the air pocket at the opposite wall of the basement depends on the slope of the drain tile.

You may or may not have basement flooding problems with your sump pump floats set the way they are. But if the air pocket is missing in places, then it is possible for the basement floor to get flooded while the level of water in the sump is well below floor level.

The suggested starting point is for the pump to turn on before more than half of the drain pipe ends are submerged. (Local code may require the pump start level to be lower.) Should you get flooding at the far side of the basement, adjust the pump turn on level to be lower still but let it run with the new setting for a week to let the soil under the floor desaturate before drawing conclusions whether your new setting is good enough.

It is best for the sump to be emptied out as much as possible before the pump turns off again. If it takes a long time for the water level in the sump to rise between rainstorms or if the water level sits still and quite high between pump restarts for days and days, that is okay.

If you are digging a new perimeter drain tile system for an existing basement, do not dig below the level of the bottom face of the foundation footings at the footings.

The advantage of optionally extending the pit downward is to allow more water to accumulate between pump starts. Fewer longer pump cycles are better than many shorter pump cycles.

 

[pnorman55]

The suggested starting point is for the pump to turn on before more than half of the drain pipe ends are submerged.

That makes sense, and maybe explains what the contractor was claiming.

Thanks much.

 

[b-boy]

The basement in my old house had this problem. We had a very high water table. The pump would kick on, empty the pit, and be followed by a rush of water out of the filled drain tiles, which would slow as the pit refilled. This was year-round except for maybe 1-2 months during the summer.

I lived there 20 years without any water seepage into the basement. The rush of water was pretty loud, and I did go through a lot of sump pumps because of the constant recycling. Other than that it never seemed to cause any problems.

Any chance you could find another pump with an adjustable switch? This might allow you to have the pump kick on sooner. However, that will probably just increase the frequency of your pump cycling.

 

[AllanJ]

My own recommendation is for the sump to have 3 cubic feet (a little over 20 gallons) of space below the drain pipes and not filled with rocks and gravel. You would have to custom pour a concrete sump or build it with bricks since very few plastic sump liners are that size. An existing small sump is probably also small enough in diameter that retrofitting it with more volume deeper down and lining it to prevent cave in is very difficult.

A larger volume of accumulated water means the pump is working on it for more time. This also gives more time for the tremendous rush of queued up water in the drain pipes to come into the sump and be pumped out during the same cycle rather than have to wait until the next cycle

Except that accumulating more water by letting the water level go higher runs the risk of eliminating the air pocket here and there around the drain tiles and then run the risk of flooding the floor at the opposite side of the basement.

 

[Ghostmaker]

You have a storm drain pump, not a sewage pump. I see no relevance of a quote on sewage pumps.

So your good with undermining the foundation?

 

[Ghostmaker]

So, in everyday language.... the pump should kick in when the water rises to within 2 inches of the drain tile input to the sump?

By the way, I see that your quote is from the International Plumbing Code chapter on Sanitary Drainage. Does that apply to a non-sanitary sump?

Thanks.

No it doesn't my mistake.:vs_worry:

 

[Daniel Holzman]

I have no idea where the theory that you need an air pocket in a perimeter drain for it to function correctly comes from. I have designed more than 10 perimeter drain system for commercial buildings, and I have a drain system in my house. None of the system I have designed have included an air pocket, and they all worked just fine.

There are only a few requirements for a drainage system to function correctly.

1. The drain pipes need to be perforated with the holes down to collect the water. They should be packed around with crushed stone and filter fabric to keep out the fines.
2. The drain pipes need to be flat or pitch slightly downhill to the sump. I normally lay the pipes flat.
3. The pipes need to be sufficiently below the floor level to maintain the water table at the desired elevation, typically 6 - 12 inches below the floor level.
4. The sump pit should be large enough to prevent short cycling of the pump.
5. The pipes can run into the pit at any elevation. Mine run into my pit about 10 inches below floor level. My pit is about 14 inches deep. My pump does not turn on until the water is about 4 inches below floor level, and it turns off with about 6 inches of water left in the sump pit. This prevents the pump from overheating, as most submersible pumps are not designed to drain the sump dry.

Maybe someone can explain the physics behind the claimed need for an air pocket in the pipes, when my pipes are running, there is no air in them, and they work just fine, as have all the other systems I have designed.

 

[lenaitch]

I'm thinking that somebody thinks you need air behind water for it to flow (like holding your finger over the end of a straw full of water) but drain lines are (hopefully) never completely full of water - the air space at the top of the lines will prevent any suction.

 

[concretemasonry]

Daniel -
I also have never understood the concept of an "air cavity/pocket or bubble". It seems like it is a canned or excuse.

pnorman55 -
My experiences - For residential basements, I feel it is best to install the rigid PVC drain tile with the bottom of the pipe below the bottom of the footing with 2" of well drained aggregate under it (the cheaper, lazier alternative of slotted corrugated pipe can work if done properly).

This applies to either interior or exterior drain tile, but I know of builders that automatically used both interior and exterior PVC tile and linked them together for insurance plus no problems with walls moving, cracking or settling because of saturated exterior soil pressures. In addition, it also minimizes the water leakage from any floor cracks or movement of the saturated soil under the slab.

Keep in mind that a basement is the lowest point of your home and can be subject to constant moisture in most areas. Moisture below ground is not like turning a faucet on or off. It is a relatively constant item, but can vary daily, monthly or yearly and must accounted for when building and altering.

Dick

 

[AllanJ]

No air pocket is the same way of saying that the ground under the house, including the perimeter drain trench and drain tile inside, is continuously saturated/filled with water. The varying porosity of the soil may or may not result in capillary action holding water above basement floor level even though the water level in the sump is below floor level. Some seepage can result through the joint between floor slab and foundation wall where the basement interior acts as an air pocket.

I am not sure whether the term hydrostatic pressure can be used to describe quantitatively when or if this kind of basement flooding under these conditions might occur.

In summer in most locations, the ground temperature averages many degrees below outside air temperature. This results in a higher humidity of the air in the basement compared with the air upstairs given reasonable air exchange between interior and exterior. Sometimes the air has a starting relative humidity high enought that when the air is cooled by the foundation walls, water condenses out.

You may not excavate below the level of the bottoms of the footings all along the foundation for the purpose of installing new drain tiles or for any other reason otherwise the foundation may collapse. But you can get away with digging a trench less than a foot wide crossing under the foundation footing, say, for the purpose of interconnecting exterior drain tiles with interior drain tiles.

 

[SHEPLMBR]

You can always adjust the float on your pump.