Soakaway - water table level?

Peter500 · 29 Oct 2020

I've dug a hole for a soakaway (1400mm deep). When I got to the bottom I found that it started puddling. The low spots had puddles but the high spots didn't. I'm wondering whether this is the water table or whether it's just because we've had loads of rain recently (everything is soggy on the surface for example). The ground at that depth is really nice sand. Does anybody know whether this is normal and ok?

My plan is to dig deeper tomorrow eg. 500mm and see whether it is all full of water or whether the puddle just drops down. I guess I should also leave it a few minutes after digging deeper to give it a chance to fill up. I did pick up a single digger bucket earlier today and the water seemed to rush into the new hole.

I was initially going to do a percolation test and trial site assessment hole to find the water table level but building control said I didn't need to do that for an extension. It does seem strange that I wouldn't need to do these tests though as how else would we know whether the site is suitable?

Ian H · 29 Oct 2020

I’d do a perk test anyway.

Although if you drop your rainwater into the water table would it make much difference?

Peter500 · 29 Oct 2020

Ian H said:
I’d do a perk test anyway.

Although if you drop your rainwater into the water table would it make much difference?

I can't really do a perc test after digging the hole as the perc test is done with a smaller hole and at a higher level. I'd also need to wait for some dry weather to get accurate results.

If the water table meets the bottom of the soakaway then I believe the water wouldn't soakaway, it would just sit there.

^woody^ · 29 Oct 2020

If the hole does not fill up the top, then its suitable for a soak-away. It's deep enough.

Ian H · 29 Oct 2020

You dig a 300mm square pit where you want the soakaway and time the water soaking away between 75 and 25% of the hole.

If the water table is there and you add to it I don’t think you would raise it’s level.

Peter500 · 7 Nov 2020

I've had a few dry days here but the hole still had a lot of water in it. It took about an hour to pump out the water but then it gradually filled up again. Does anybody know whether the water is coming from the surrounding soil or whether it's the water table? The level ended up to approx. 150mm lower than it was but I may find the level higher in the morning. It's frustrating as I can't see the bottom and get it level to finish the soakaway.

btw. there are still puddles at the surface too.

Old Salt · 7 Nov 2020

I can’t help, this is soak away number 2 in progress

Peter500 · 7 Nov 2020

Old Salt said:
I can’t help, this is soak away number 2 in progress

My hole looks a lot better than that. Was that filled when it rained or did the water flow into it when it was being dug?

jacko555 · 7 Nov 2020

I've no experience with soakaways but your pic looks lile you're uphill a bit / on higher ground, compared to the road?
Would the water table be that high?
Saw an episode of Grand Designs once, the amount of water on site meant a massive spend on deep foundations.
After they were laid, turns out there was a leaking water main causing it.
Not saying this is that, but, from the pic you look like higher ground (unless you are in a valley) and unless flooding is commmon place, seems odd?

Old Salt · 7 Nov 2020

Water ran into it from soak away number one which is actually under the digger. 8 crates were used and now laying french drains to try and keep water from flowing down the drive and across the pavement. You can see it in the background of the photo. I believe this is actually the water table, as we are on clay and there was a natural pond 25 metres north west about 100 years ago.

jacko555 · 7 Nov 2020

Cripes.

Old Salt · 7 Nov 2020

Dont want to highjack this thread but for info we are on a rise approx 3 metres above the roadway. Both front and back gardens can get water logged if we have heavy rain. The photo was taken after 3 dry days following a week of heavy rain. The drive now has an aco drain to catch the water and a pipe to lead it to the soakaway. The damp proof course at the rear of the property is about 150mm and at the front about a metre above ground level.

Ian H · 8 Nov 2020

Peter500 said:
I've had a few dry days here but the hole still had a lot of water in it. It took about an hour to pump out the water but then it gradually filled up again. Does anybody know whether the water is coming from the surrounding soil or whether it's the water table? The level ended up to approx. 150mm lower than it was but I may find the level higher in the morning. It's frustrating as I can't see the bottom and get it level to finish the soakaway.

btw. there are still puddles at the surface too.

What if you add water to it? Does it rise then settle?

Peter500 · 8 Nov 2020

Ian H said:
What if you add water to it? Does it rise then settle?

It would take a lot of water to do that as the hole is almost 4m2. I also think this would settle either way. The lower part is made of sand which should drain easily.

The water in the hole returned to almost (but not quite) its original height over night. Not sure whether that just means the surrounding ground is saturated or whether it's the water table.

Londoner2 · 9 Nov 2020

When foundations were dug for my extension, water was puddling at depth of 1.2m, house is in a flood plain, when it rains heavy for 24 hours non stop most of the garden fills with water (house never flooded as too high). Local people who built extensions also said same thing.

A soakway for roof water was out of the question for me because of the water table, only solution was 2 large water butts which the silly council accepted, however i never fitted them, my roof water has a long pipe under the patio exiting to the garden.

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Soakaway - water table level?

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