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Perculation Test Results Problem


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Hi

We have bought a large plot (3rd acre) to build a house. We have dung 3 perculation test holes 80cm deep and conducted the tests several times. One of the holes drains well, the other two holes take longer than the permitted time. 

We can't discharge to a water course. Even though we have a large plot if we meet all the requirements for distance from the house for the treatment plant and soakaway we only really have one location. 

Does anyone have any idea what we can do to make this work? 

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Research your SUDS options it’s a big subject and a big headache, but doable. It depends on if it’s a planning condition or Building Control are to be satisfied. Is the good spot not suitable for a soak away? 
 

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Is it possible to organise things to allow you to use the area that passed for the drainage field? We also only had one area suitable for a drainage field. Ours was further complicated by having two boreholes nearby and a running water course. 

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Loads of options these days.

 

Drainage mound, boreholes, larger attenuation tunnels, having a huge drainage field. All are better options coupled with a package treatment plant that using a cesspool. I would recommend approaching a decent drainage firm for some help on site.

 

What is the geological footprint where you are (clay/chalk/sand etc and how far down), and how far down is the winter water table? might be worth getting a 10t digger and digging a deep hole, seeing if you get to chalk/sand etc, or hire a borehole survey to determine if a borehole would be suitable. It is worth noting that many non standard methods will need the approval of the Environment Agency, but a decent installer/surveyor can usually guide you in what would be most suitable/acceptable.

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Is there a ditch or piped ditch along side the road?

 

If you propose a storm water surge attenuation tank you might be allowed to put the overflow into that.

 

Failing that an attenuation tank can reduce the flow rate that a soakaway or drainage mound has to deal with.

 

You can also get a combined attenuation and rainwater recycling tank, although they are bigger.

 

Where soakaways are marginal I've heard of some builders telling the council and BCO it's ok. They do build a soakaway but when the BCO isn't looking they also hide a perforated pipe alongside the foil drain pipe. In effect turning the gravel surrounding the foul drain into an additional long thin soakaway that conveniently runs off site. Only works if the land slopes the right way. 

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>>> might be worth getting a 10t digger and digging a deep hole

 

+1 even a smaller one will give you a clue. Cheaper than an SI in the 1st instance. Anything sandy and you're home and .... dry 😃.

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3 hours ago, joe90 said:

Why do you need more? Make it bigger

Perhaps you could expand this simple and good advice so that it sounds more technical for the bco.

 

There is seldom a need for expensive and complex solutions.

11 hours ago, Lincolnshire Ian said:

One of the holes drains well,

what figures do you have for the 3 tests?

does the site slope?

 

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We have a Vp of 28 in one hole and 105 and 110 in the other two. Massive difference. When I dug the holes there didn't seem to be much difference, all very dry and solid. It was a long crowbar job to loosen the soil whilst digging the hole. 

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12 hours ago, Lincolnshire Ian said:

Sorry, my post wasn't clear. The peculation test is undertaken to determine the suitability for a soakaway, it looks like the ground as it stands isn't suitable for a soakaway. 

Hi @Lincolnshire Ian

 

I wonder if you have undulating layers of different subsoils. I dug down 1.2meters and passed the test. However when digging deeper to install the crates I broke through a clay layer into a sandy shingle layer and any water even during heavy downpours just disappears ( I know because I have a 3m vertical 300mm diameter pipe installed to monitor the design) All that digging and I have never seen the level rise above one foot above the bottom of the crates! 

 

I would dig down further, shoring the sides if required and see if it improves.

 

Good luck

 

Marvin

Edited by Marvin
minor change.
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3 hours ago, Lincolnshire Ian said:

We have a Vp of 28

That is very suitable surely.Why is this one area so much better? Perhaps the ground is broken up by long gone tree roots.

 

Show the result to the bco and work out the length of French drain that works, and/or  add a pit.

 

Fundamentally this water must not run off your site. That is all you have to resolve. Some bco's are relaxed about allowing old-fashioned rubble- filled soakaways.

 

Also discuss the soakaway for the foul outfall.  I think the regulations are crazily onerous on this and your bco may agree.

 

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