Soakaway Nightmare, Clay Soil

25 Oct 2016
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United Kingdom
Hi All,

I'm looking for some advice, if there is any that can be given :(

I'm in the midst of planning a large extension, and the last part of the building warrant requirement if the approval of a rainwater soakaway design. the roof is 180m2

We had a failed percolation test (the water didnt move a mm) within our existing boundaries, which i put down to the soil etc we acquired to fill in the large pond that had been installed when we first moved in.

we've progressed little since then its been over a year.

As it happens we've just purchased an acre of land to install a new track/drive.The land wraps around our existing gardens,

great I though, We'll slap a soakaway in there and there'll be no issue, I can access with my digger and dig a big hole,

well I did that yesterday, I dug two holes, both the same

roughly 2m x 1m, x 1.4m deep (hit rock)

As you can see from the pictures, it looks like clay and certainly acts like clay

filled the hole at 1820, and by 2217 it had possibly (possibly) moved 2cm, but I suspect thats more hope than anything

Does anyone have any experience of creating a miracle soakaway

We are very rural, and theres no sewer or field drainage nearby, so it looks like we may be completely stuck.



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I'm no expert on soakaways but how about a longer, shallower herringbone type?

It would give much more surface area for the water to soak into and if it's shallower it could go into the soil.
Do you harvest rain water for use in the house. If not then consider it as that will reduce the amount of rain that will have to soak away ( and reduce your water bill )

Where do you dispose of your sewage ? Is it a private cess pit or similar with a soak away somewhere ? could the area around that soak away be suitable for the rain waer soak away as well. Provide the addition of rain water to the area does not prevent the effluent soaking away properly
Hi, thanks for getting back to me

The structural engineer from the previous failed percolation test expressed surprise that any soakaway would work.
My foul water is disposed off via septic tank and soakaway, and I suspect the puddle of water in the field beside the fould water soakaway indicates that the effluent is not draining very effectively. not good.

I'll look into herringbone soakaways
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I had the same issue, and got agreement from SEPIA to use a tunnel system that site shallow in the top soil. Might be worth a look at.
If your are rural where do your farmers fields run to? You may beable to get permission to discharge into a dyke.
Morning All,

thanks for getting back to me I appreciate it

I had a long chat with Building Control Yesterday who basically pointed me back to my structural engineer, however he suggested I may have been unluck ot hit rock in the three trenches as others have managed to dig through clay to a better draining layer. I have my doubts, but I'll try again at the weekend.

In the mean time I've asked the farmers wife (she's the contact) if they have any knowledge of field drains in that field, she said she'd have a look and get back to me. There is a dyke at the opposite end of the field (150m away)/

I've had a look on google maps to see if I could identify any possible field drain pattern from satellite, and there is one promising lead which starts inside the plot I just bought so I'll have a go at that again.

The ground conditions itself are circa 40-50cm of topsoil then clay. It looks to me like the topsoil does all the drainage as the water level has dropped (after 24 hours) to just above the bottom of the topsoil. It may have taken such a long time as the field itself is sodden from a lot of rain.

I'll also look into soakaway tunnels. ta
I'd be cautious on relying on field drains for that volume of water, if they've been there a few years could possibly be silted/scaled up internally, and all you'll do is move the problem along. I think you'll be best looking to start from scratch.
The same amount of rainwater is hitting the ground now, as when the extension is built. presumably it goes somewhere now.. you've got plenty of land. A soakaway a fair distance from the house shouldn't be an issue?..

I know what you mean logic dictates that it would be fine, show it away from the house

Building control are asking for a soakaway design that works, certified by the structural engineer involved.

He's categorically ruling out normal soakaway based on current percolation results.

I found a ground assessment from a property built reasonably close( over the field). They managed to dig through clay at 1.8 m, so I'm hoping I've been very unlucky with rocks, try again at the weekend
I am glad to report that after some further digging (and shifting some large rock) 've found a sand layer at 2.8 m, which has since passed the test
thanks for the input guys

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