Car Park sump pump pipe design 1

[richardmf]

Hello
A car park sump pump has failed where I live. The flooding is causing everyone in the block great stress and the standing water is causing a health hazard for our children. The carpark is in a basement, below the water table, and this pump extracts any water ingress.
The pump has failed after only 20 months and I suspect it is due to the pipework design. I would like to see if you experts agree or if you could improve my thinking?

See the photo of the pipework design. There is a pump below in the sump that has a 2" pipe. The water is then pushed uphill where the pipe becomes 6". I suspect that the added load to the pump is shortening the life of the pump?

Would you recommend that the 2" continues all the way when we replace the pump? Or do we need a larger pump? Any other thoughts?

Many thanks again for your help

Richard

 

[beej67]

I don't see an attachment.

A 6" pipe should have less headloss than a 2" pipe does. There might be a junction loss at the expansion joint, but I doubt it would be significant. If I understand what you're describing, I doubt the widening of the pipe to 6" would have an adverse effect on the pump.

I would guess that the main problem is the carport was built below the groundwater table, so the pump is always running, and it burned out. That's pretty terrible engineering practice. You should identify the source of the groundwater itself and fix that.

I suspect you may be getting groundwater in or near your foundation because of poor site drainage. This is quite common, and usually easy to fix with site improvements, such as piping all your gutters downgradient, intercepting offsite flows and directing them around and away from your home, and making sure that no water is jumping the gutter from your street and going down your driveway. Look at all that.

If the carport is lower than the regional groundwater table, as experienced not only on your land but on neighbors land, then you have a major issue to deal with, and it shouldn't be handled by a sump pump in your carport, because the flow of water from the surrounding groundwater table into your carport will cause structural damage to your house in the long term. You may be able to fix it with an underground perimeter french drain to an exterior sump pump and some waterproofing, but that will be more expensive than the site improvements listed above. That also might not be legal, depending on where you're at. Some places make you pull a permit for any permanent dewatering operation, but honestly those places usually also have rules preventing you from building stuff below the regional groundwater table.

Get some post hole diggers and dig a test pit deeper than your carport in the four corners of your yard. See how much they fill up in a dry period, and whether they fill up higher than your carport. If they don't, then your problem is probably due to surface water intrusion along your foundation, and can be fixed with site improvements. If they do, you might be in a more expensive pickle.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[chicopee]

You'll need to get the pump performance curve to determine if the pressure loss thru a 2" pipe,for the height and length that is required at your site, is not exceeded at the expected flow rate. I suspect that the added 6" pipe was to reduce the head loss increase that a 2" line would have given you.

 

[Pinwards]

beej67 I think there's a little confusion in terminology. I believe the OP is probably from across the pond, and in their parlance Car Park = Parking Lot, not carport. He says it's in the basement which makes me picture an underground parking garage under a larger building, not a single house. Your concerns and recommendations are still mostly valid, just on a larger scale. They still need to analyze the source of the water (poor surface runoff handling, high groundwater, etc.) to see if it can be diverted to minimize the problem, or quantified before you can properly design the pump or other solution.

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[beej67]

Aha! Have a gold star sir. Thanks.

Yeah, if that's a sump pump in the basement of a parking garage, then it's a different scale of problem entirely.

The biggest culprit for those things in my experience is either site grading at the curb cut, or failure to route runoff from the top level to the municipal storm sewer system. In either case, you get runoff into the bottom level of the vault that you didn't anticipate, either down the access ramps from the top level, or potentially into the deck itself from the street. Step one for me would be to check the capacity of trench drains, make sure they're not clogged, and make sure all surface water is getting intercepted before it gets into the deck.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com