Massive water flow into sump pit

[itsnotrequired]

I have recently purchased a new home in Chicago and we had a very heavy rain last night. Water was pouring into our sump pit at such a tremendous rate that both the main and battery backup sump pumps were running just to keep up. It was unreal how much water was pouring into the pit. Some specifics of our setup:

- main pump is Zoeller 98-series cast iron (3600 GPH at 10' head)
- backup pump is Basement Watchdog Special battery powered (1750 GPH at 10' head)
- both pumps discharge to city sewer with in-line check valves (approx. 10' from pump intake to highest pipe point)
- both pumps rest on raised bricks in the pit (i.e. they are not resting on dirt)
- poured basement walls, basement floor roughly 9' below grade
- home and entire development is on level ground (i.e. not at the base of a hill or valley) and there are no streams, lakes, etc. nearby
- 4" drain tile system around exterior and interior of foundation, empties into sump pit
- clay soil, no lawn installed yet
- downspout extenders installed to direct water away from home (flow toward street or to storm drain in back yard)
- houses adjacent to ours only 5 feet apart, same design as ours, have sump pits, gutters with downspout extenders and no lawns

This last storm totaled less than an inch of rain. Both pumps were running continuously for an hour and the main pump then ran continually for nearly another hour. It then ran intermittently for about another half hour. The water flowing in was brown with dissolved sediment or silt (no large particles like sand). I've dug around at the pump intakes and as near as I can tell, nothing is stuck in the intakes and reducing flow.

Based on the times and pumping capacity of the pumps, it appears as if I pumped nearly 10,000 gallons all told from this last storm. If an inch of rain is assumed (more than actually fell) and all the water was pumped (i.e. the ground absorbed nothing), then we're talking about an area of 126' x 126'. My whole lot is only 40' x 110'!

So what the heck is going on here? I understand a lawn will help with water shedding but this is ridiculous. Based on my numbers, it is as if I'm pumping all the water for me and my neighbors and then some. They have seen this water flowing into my pit and say that they never have flows that extreme. My thoughts:

1. My home is a few inches lower than the neighbors and thus a natural low spot.

2. Builder somehow tied neighbors drain tile into mine.

3. Catch basin for storm drain behind house is leaking and excess water is flowing into my drain tile system.

Anyone have any experience with massive flows such as this? Any other ideas?

 

[bimr]

Normally the sump pump is piped to the storm sewer not the sanitary sewer. However, you may be in an area with combined sewers.

The ground around your new house was probably not compacted properly and will allow water to quickly seep through the ground into the drain tile.

Since you are so close to the neighbor, you are probably receiving drainage from his property as well.

You have pointed out that you have the lowest elevation in the immediate vicinity. Water moves to the lowest elevation.


Suggestions:

You might try to direct the downspouts into the street, catch basin, or as far away as possible. Have the neighbor move his downspouts as well.

Consider buying a larger backup pump. You may experience a Com-Ed power failure and have your basement flooded.

Check the pump capacity. You say that you are pumping up from a 9' deep basement with a pump with 10' of head. You have not stated the discharge pipe length or diameter. There is additional headloss in the pipe that must be taken into consideration. If you are pumping into a small pipe with a high headloss, your pump capacity is reduced.

 

[itsnotrequired]

- Chicago has a combined sewer system. The pumps are piped into the sewer line. The sewer cleanout for our house is not yet capped and water can be seen flowing freely in the pipe. In other words, I am not pumping against sewer back-pressure.

- The sump pit is right next to the main discharge to the city sewer. There is a 90 degree elbow on the sump discharges before gravity takes over. The overall horizontal run is less than 3' Even assuming an ultra-conservitive head of 15', we're still talking about 8,000+ gallons of water.

- I already have downspout extenders that direct water toward the street and catch basin. Since no lawn is in yet, I actually have a small trench routing the water to the catch basin. It flows like a river right into the storm drain. Sure, some water is still being absorbed but the vast majority flows right into the drain.

- My basement is lower than the homes across the street but still at the same level of all the homes on my side of the street. In any event, my neighbors are pumping very little extra water while I am pumping way, way more than i should be.

The pipe from the catch basin to the main street sewer runs between me and my neighbor's home. My latest thought is that the stone put in around my drain tile and this pipe are one and the same. My drain tile is probably even lower than the the storm drain line. I'm guessing that ground water is travelling along the storm water stone, into my stone and then into my drain tile.

 

[bimr]

You can use dye to confirm your analysis.

Note also that if you have gravel under your basement floor slab, it will act as a conduit to transfer water.

 

[cvg]

since your lawn is not in yet, you might consider regrading the area between homes to direct your neighbors runoff away from your house

with clay soil, you should not see this level of flow as the soil should have a low permeability. this indicates a direct connection to the storm drain runoff and your sump was obviously not designed for this condition. First, I would put your homebuilder on alert (call your attorney), as the repair could be quite expensive. And the damage from flooding when your pump fails will also be quite costly.

 

[itsnotrequired]

I let the developer know about the situation today. He was quite surprised with the flow totals. He indicated no one else in the development has reported anything like this. He is letting the builder know about the situation and will get back to me this afternoon with an idea of how they will tackle this.

Our basement is unfinished and I don't have anything down there so I'm not too nervous if it floods again. But if I ever want to use my basement, they will need to address this issue. The home next to me hasn't closed yet and I'm sure the developer doesn't want to be dealing with the same situation next door.

The more I think about this, the more I believe that the storm drain next to my foundation is broken...

 

[eric1037]

You obviously don't want your basement to flood if you have a combined sewer system and the sewer pipe is broken. Yuck!

 

[cvg]

ditto! been there, done that and I'm scarred for life

 

[itsnotrequired]

I believe the actual sewer pipe in the street and the main sewer drain from our house is just fine. What I think is busted is the pipe that connects the storm drain in the backyard to the main sewer line. Unless the neighbor is taking a crap in my backyard, I should be fine.