My foundations trenches have not been backfilled yet following the first two courses of footing blockwork and I am now seeing some standing water collecting after heavy rain.

 

I am not sure what type of pump to buy to drain off the water. A dirty water pump sounds useful but a reviewer commented that they cannot suck up the final 50mm to 70mm of water.

 

Puddle pumps are good for sucking up a pool of water down to a few mm however I am concerned such a design would gum up with the assorted debris in my trenches. In all cases the base of the collected water is my original foundation concrete which is 450mm below ground level and the deeper pools are, you guessed it, 50mm to 70mm.

 

What type of water pump should I buy for this situation? I am not looking for an automated setup.

As we are almost classed as a bog I bought a cheap “sump pump” on Ebay, yes they will not pump the last 50mm but when the trenches were dug we dug out a sump (200mm lower than trench bottom) about a foot square, adjacent to the trench, just make sure you remove the pump before filling with concrete?

7 minutes ago, joe90 said:

As we are almost classed as a bog I bought a cheap “sump pump” on Ebay, yes they will not pump the last 50mm but when the trenches were dug we dug out a sump (200mm lower than trench bottom) about a foot square, adjacent to the trench, just make sure you remove the pump before filling with concrete?

 

 

Your post got me thinking... although my situation is different to yours because my trenches have been part filled by foundation concrete to 600mm with footing blockwork on top. What I might do is dig a mud sump adjacent to the poured concrete at the low point of each water pool. If the mud sump is 100mm below the top of the current concrete pool base this should drain things near 100%.

 

I want to get a system in place before the site experiences too many freeze/thaw cycles.

Why do you need to pump the water out?  What are you backfilling with?  If this is all substructure, water will not be an issue.

I half buried an old bucket in one trench that we had to keep pumping out.  I drilled holes around the top edge, just about the depth it was buried to, and added some lumps of crushed concrete in the bottom to hold it down.  The pump sat on that, and effectively drained all the water from the trench.  The only slight snag I found was that the float switch would sometimes get caught by the side of the bucket and not drop down enough to turn the pump off.  Not really a problem if you keep an eye on it.

17 minutes ago, Mr Punter said:

Why do you need to pump the water out?  What are you backfilling with?  If this is all substructure, water will not be an issue.

 

 

I have a service trench at the same depth nearby the foundation trenches and this is dry so we are not talking about a rising winter water table. The water is surface runoff mostly from the exposed oversite.

 

Not sure what you mean by "substructure" but I am talking about pooling water rising to 700mm below the yet to be reached dpc level. Most footing blockwork is heavy 19kg concrete blocks though the garage footings start with 1 course a thermolite like trenchblocks which I understand are not so resilient to freeze thaw cycles.

 

Once my long term drainage is complete and the cavity fill in place the trench backfill will be the old excavated subsoil still onsite.

29 minutes ago, JSHarris said:

I half buried an old bucket in one trench that we had to keep pumping out.  I drilled holes around the top edge, just about the depth it was buried to, 

 

I found a US YouTube video that did something similar and they also wrapped the bucket in permeable membrane to stop the sump from silting up. However that was for a permanent installation to drain a cellar.

I just bought a cheap dirty water pump from Screwfix and as long as there is a bit of a sump it will empty it.  

 

Tip if / when it breaks within guarantee, SF will not ask for the old one back because it is "dirty" and just send a replacement.

Substructure is all the parts of the building below ground. Unless you plan to leave the site as is for several years there will be no issue with freeze / thaw.

We only used the pump for two or three weeks.  It was a deep service trench right along our boundary that, amongst other things, had a DNO main power cable to go into it, feeding other properties.  We were being dicked around by the DNO connection team, so had to keep the trench open until they finally got their act together.  The trench was probably half a metre below the local water table, so every morning it would be half full of water, which we'd then have to pump out, as the water tended to make the sides of the trench fall in.