HELP, failed perc test and on clay soil

[nowtie]

17 hours ago, Jilly said:

It’s probably not worth doing it then. But you can propose something else which you can prove works. 

That's the issue, there are no other options left now other than re-do the perc tests all over the site and try find one that works?

[nowtie]

On 20/06/2024 at 23:27, Alan Ambrose said:

Do you have a soil investigation and/or have you looked up BGS records of any bores nearby. It would be interesting to see how deep the clay is and what’s under it.

Hi Alan

Thanks for responding. I have just gone to the BGS website and it looks like there's something on the same road but I'm struggling to interpret the data, can you help? Plus it looks like a well and not a borehole soakaway?

 

Reference: ST23NW12
Name: XXXXXX
Water Well Reference: ST23/2
Precision: ± 10 METRES
Length (m): Unknown
Date:
Easting: 324550
Northing: 137700
Scan Quality: not Entered
Record: Scan

 

Who could do a soil investigation? I've already spoken to a few geotechnical engineers who have told me a borehole soakaway wouldn't work there (although have spoken to another who says it would)

[nowtie]

19 hours ago, Blooda said:

It goes into the foul sewer, but attenuated to 2l/s. 

This is when it reaches 55% full

 

Example of drainage hierarchy. [will be the same or similar for wessex water] 

 

The Drainage Hierarchy | Essex Design Guide

 

Looks like you are at the combined sewer stage.

 

Ahh is that a foul only sewer? OK we've had a no from Wessex Water to discharge into their foul only sewer due to the fact that there's a gully drain in front of the property and said we need to discuss with Highways. Highways have said no. Perhaps it's worth going back to Wessex? I'm not sure what you mean by "looks like you are at combined sewer stage"? We don't have a combined sewer anywhere near the site?

Thanks for the drainage hierarchy. Yes we have one of those but still struggling!

[Alan Ambrose]

>>> I have just gone to the BGS website and it looks like there's something on the same road but I'm struggling to interpret the data, can you help?

 

Ping me your site's postcode and I'll take a look at BGS. Or post up any nearby reports here and more knowledgeable people than me will chip in too. This is the kind of thing (from a 1941 borehole report maybe 3/4 mile away from my plot).

 

It shows clay to about 20m and then sand under. If you found, say, sand closer to the surface, that would help a lot...

 

 

 

[Dave Jones]

53 minutes ago, nowtie said:

Good question! In hindsight we should have persevered with take soakaway/storage crate solution. What are your thoughts on us going back to planning and saying we have now dug different test holes with different results (which work)? Or is that ridiculous idea? 

 

all they want is a perc test report. make one yourself, sign it and its done.

[nowtie]

1 hour ago, Dave Jones said:

 

all they want is a perc test report. make one yourself, sign it and its done.

OK thanks Dave. You don't think they'd question why we're re-submitting the perc tests as successful when we'd already submitted them as not?

[Blooda]

1 hour ago, nowtie said:

Ahh is that a foul only sewer? OK we've had a no from Wessex Water to discharge into their foul only sewer due to the fact that there's a gully drain in front of the property and said we need to discuss with Highways. Highways have said no. Perhaps it's worth going back to Wessex? I'm not sure what you mean by "looks like you are at combined sewer stage"? We don't have a combined sewer anywhere near the site?

Thanks for the drainage hierarchy. Yes we have one of those but still struggling!

 

 

The foul sewer can accept a certain amount of rain water, in fact the water board like a bit to be added as it helps keep the lumps moving.  What  they may not stand is a massive deluge in a storm [hence the attenuation at a controlled max flow rate] 

You need to go back to the water board say you have explored [with evidence] all the higher level solutions in the hierarchy and then see what they say.

 

 

 

 

[nowtie]

1 hour ago, Alan Ambrose said:

>>> I have just gone to the BGS website and it looks like there's something on the same road but I'm struggling to interpret the data, can you help?

 

Ping me your site's postcode and I'll take a look at BGS. Or post up any nearby reports here and more knowledgeable people than me will chip in too. This is the kind of thing (from a 1941 borehole report maybe 3/4 mile away from my plot).

 

It shows clay to about 20m and then sand under. If you found, say, sand closer to the surface, that would help a lot...

 

 

 

Thank you so much. Is there anyway I can private message you with the report? I've managed to save a PDF of the BGS report. Many thanks

[nowtie]

3 minutes ago, Blooda said:

 

 

The foul sewer can accept a certain amount of rain water, in fact the water board like a bit to be added as it helps keep the lumps moving.  What  they may not stand is a massive deluge in a storm [hence the attenuation at a controlled max flow rate] 

You need to go back to the water board say you have explored [with evidence] all the higher level solutions in the hierarchy and then see what they say.

 

 

 

 

Ahh that's really interesting to read actually. I keep asking our drainage engineers the feasibility of going back to Wessex and they keep saying it's not an option. Wessex has a SUDS hierarchy which we have followed and yes it does seem in their policy that could be an option to discharge IF we have exhausted all the hierarchy but they're currently saying no due to the Highways gully. So I have emailed Wessex to see if there is any manoeuvrability so thank you so much. I'll keep you posted. 

[joe90]

1 hour ago, nowtie said:

OK thanks Dave. You don't think they'd question why we're re-submitting the perc tests as successful when we'd already submitted them as not?

No tell them you dug in another part of your property 🤷‍♂️, might be worth getting a small digger in and dig a few deep holes in various places to see if better results can be found. 

[nowtie]

11 minutes ago, joe90 said:

No tell them you dug in another part of your property 🤷‍♂️, might be worth getting a small digger in and dig a few deep holes in various places to see if better results can be found. 

Roger that, thanks Joe  We've got our own JCB (well husbands) Already gone down 1.2m and 2.4m but will try other areas on the site and at different depths. Hopefully they won't question the U-turn?

[Dave Jones]

1 hour ago, nowtie said:

OK thanks Dave. You don't think they'd question why we're re-submitting the perc tests as successful when we'd already submitted them as not?

 

nope, different area worked ok. They really don't care.

[nowtie]

11 minutes ago, Dave Jones said:

 

nope, different area worked ok. They really don't care.

OK this is great, are you sure?? Do you know of anyone who has done this before?!  I'm going to tell husband we'll re-do the perc tets (he is saying "I told you we should have done this in the first place") It's been MASSIVELY costly so far with having to get drainage engineers involved (who it seems now they have their money have washed their hands of the whole thing and are telling me just to wait for Highways to get back to me...meanwhile the planning consultant is telling me we might never get a definitive yes from them to discharge into their gully since it's overloaded anyway...)

[Dave Jones]

19 minutes ago, nowtie said:

OK this is great, are you sure?? Do you know of anyone who has done this before?!  I'm going to tell husband we'll re-do the perc tets (he is saying "I told you we should have done this in the first place") It's been MASSIVELY costly so far with having to get drainage engineers involved (who it seems now they have their money have washed their hands of the whole thing and are telling me just to wait for Highways to get back to me...meanwhile the planning consultant is telling me we might never get a definitive yes from them to discharge into their gully since it's overloaded anyway...)

 

 

new test pit, new results. Perfectly fine.

[Alan Ambrose]

@nowtie >>> Is there anyway I can private message you with the report?

 

I think you can attach it to a private message, but you could just post the link up here, or just the strata bit if you don't want to post the whole thing.

[saveasteading]

I'm appalled at people telling you to cheat. Are people living in houses they built? What have they missed out or fudged?

I'd like to think it is ignorance rather than principle.

 

Let's go back to first principles. The authorities are trying to reduce load on the sewage works and sewers, and to avoid flooding.

 

If all driveways are porous then they are not in the equation. Where does / did the existing roof water go?

How much land is there and do you have slopes?

I'm confident this can be done. Properly.

 

 

[nowtie]

1 hour ago, saveasteading said:

I'm appalled at people telling you to cheat. Are people living in houses they built? What have they missed out or fudged?

I'd like to think it is ignorance rather than principle.

 

Let's go back to first principles. The authorities are trying to reduce load on the sewage works and sewers, and to avoid flooding.

 

If all driveways are porous then they are not in the equation. Where does / did the existing roof water go?

How much land is there and do you have slopes?

I'm confident this can be done. Properly.

 

 

Hi

I think they're suggesting I try different test holes in different locations? We're going to try again next week. My husband is a farmer/builder and so does a lot of land drainage on farm and said he can make it soak away from both properties by digging a 90m french drain in length all the way down the site (it's long and narrow) if we did do attenuation/soakaway option.

Well we have now demolished the bungalow but CCTV reported it was just going into the ground...so ultimately Highways gully drain outside the front of the property. We've been trying to say that we'll reduce the uncontrolled run off rate and better what is there at the moment. This would be all fine but we also have permission to build another detached dwelling in the garden of where the bungalow was so this one is the one we'd struggle with for the surface water.

 

Land is 0.4 acre and it's awkward shape, very narrow. I attach the location plan. Blue is the land I own. Red outline is new detached dwelling. To left is existing bungalow which weve had full planning to demolish (done) and re-build. The slope is marginal but it does slope gently down towards the narrow section (hence wanting to put a linear french drain along the whole length of site...but it has to be 5m from highway so not even sure if this is possible)

 

Thanks for your help

[saveasteading]

34 minutes ago, nowtie said:

digging a 90m french drain 

Ideal. There is an enormous surface area to the sides and bottom of the trench so even a poorly percolating clay will take it.

And the sheer volume of pipe and gaps in gravel  will hold stormwater until it disappears. 

Also i see lots of trees. They will dry out the ground in summer, and the roots will have formed crevices through the clay. The tests may work better there.

The 5m guidance  shouldn't apply to a shallow French drain, but distance will avoid your pipe taking road water.

 

Barrels on downpipes also helps to take the first flush of a storm. In winter you can open the tap to a dribble, to empty them slowly before the next storm. All such should be accepted by planner or bco.

They might be suspicious of a good percolation figure though.

 

A lagoon or swale is useful but I don't know if the topography allows it.

 

40 minutes ago, nowtie said:

they're suggesting I try different test holes in different locations

Some this and others I think suggesting you make up some numbers. 

[nowtie]

18 minutes ago, saveasteading said:

Ideal. There is an enormous surface area to the sides and bottom of the trench so even a poorly percolating clay will take it.

And the sheer volume of pipe and gaps in gravel  will hold stormwater until it disappears. 

Also i see lots of trees. They will dry out the ground in summer, and the roots will have formed crevices through the clay. The tests may work better there.

The 5m guidance  shouldn't apply to a shallow French drain, but distance will avoid your pipe taking road water.

 

Barrels on downpipes also helps to take the first flush of a storm. In winter you can open the tap to a dribble, to empty them slowly before the next storm. All such should be accepted by planner or bco.

They might be suspicious of a good percolation figure though.

 

A lagoon or swale is useful but I don't know if the topography allows it.

 

Some this and others I think suggesting you make up some numbers. 

Thanks for this. This is exactly what my husband suggested BUT our drainage engineers didn't seem willing to sign it off? We therefore went ahead with their idea of attenuation tank plus slow release into Highways gully drain but as I said before Highways has now said no and I'm running out of money! Could we put a plan together ourselves as the above and submit it? Just as a sidenote we're about 1.2m above the road.

This is a pre-commencement condition that we can't seem to get discharged.

[saveasteading]

1 hour ago, nowtie said:

Could we put a plan together ourselves as the above 

Yes . Plain English.  The requirement. The constraints. The site circumstances. The solution. All of that in a quick overview, then again in detail.

 

I'm happy to look over it.

1 hour ago, nowtie said:

our drainage engineers didn't seem willing to sign it off?

They are probably Structural not Civil Engineers.

Many default to holding the water then releasing it slowly as that is what the big housebuilders do.

No water leaving the site is best practice. It also reduces your drainage rates dramatically....every year for ever.

[joe90]

17 minutes ago, saveasteading said:

No water leaving the site is best practice

I agree however what happens to rainfall on the site before any building work.? The size of the site is the same so rainfall per sq m is the same, after building it will just “go” wherever faster unless attenuated.

[Dave Jones]

4 hours ago, saveasteading said:

I'm appalled at people telling you to cheat. Are people living in houses they built? What have they missed out or fudged?

I'd like to think it is ignorance rather than principle.

 

Let's go back to first principles. The authorities are trying to reduce load on the sewage works and sewers, and to avoid flooding.

 

If all driveways are porous then they are not in the equation. Where does / did the existing roof water go?

How much land is there and do you have slopes?

I'm confident this can be done. Properly.

 

 

 

its called reality.

 

Soakaways dont work in clay and never will. So you make an attenuation pit a.k.a soakaway to hold the deluge with the overflow goinjg to foul. Literally hundreds of thousands of houses like this.

 

Flooding is a totally separate issue, dredging the rivers again would be a good start.

[nowtie]

31 minutes ago, saveasteading said:

Yes . Plain English.  The requirement. The constraints. The site circumstances. The solution. All of that in a quick overview, then again in detail.

 

I'm happy to look over it.

They are probably Structural not Civil Engineers.

Many default to holding the water then releasing it slowly as that is what the big housebuilders do.

No water leaving the site is best practice. It also reduces your drainage rates dramatically....every year for ever.

Hi,

yes they're civil engineers....see extract from their website and the contact who is working on it

 

X is a privately-owned business offering civil engineering design, construction and maintenance services to domestic, commercial and public-sector clients. 

Civil Design Engineer with 18 years experience working as an infrastructure engineer in the UK and over 4 years experience working as a Civil Environmental Engineer in X

 

I had a no from 2 x previous civil engineers who just said there wasn't a solution they could sign off so I went with the above engineers. Would you mind if I PM you the details?

 

[saveasteading]

Just now, nowtie said:

Would you mind if I PM you the details?

Yes do that.  

They do look like the right people for it, maybe just not into what they see as alternative.

Maybe there is something I don't know yet. 

"No rain off site" is something I've done loads of times. It's what happened before there was a building. 

Sewage rates are charged on the amount of water you pipe in, plus a rainwater allowance. .  You have to tell them there is no rainwater to drains. 

[nowtie]

21 minutes ago, Dave Jones said:

 

its called reality.

 

Soakaways dont work in clay and never will. So you make an attenuation pit a.k.a soakaway to hold the deluge with the overflow goinjg to foul. Literally hundreds of thousands of houses like this.

 

Flooding is a totally separate issue, dredging the rivers again would be a good start.

This all sounds like what we're proposing but we've had a no from Wessex water to overflow the surface water into the foul hence why we're now stuck