Garden Drainage - Recent Build on Brownfield Site

Garden Drainage - Recent Build on Brownfield Site

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grantone

Original Poster:

640 posts

172 months

Thursday 12th April 2018
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I could do with some advice on improving the drainage in my garden.

It's a small west-facing garden in the suburbs of Manchester, house built about 15 years ago on a brownfield site. Our son is turning 2 and the garden was just too soggy for him to play on most of the time. I've lifted the turf and dug a few test holes and we've got about 8 inches of heavily compacted top soil, underneath that across most of the garden is 4 or 5 inches of concrete and under that as far as I've managed to dig so far is rubble and hardcore. I've given up digging manually at about 18 inches down.

Water just doesn't drain anywhere, I bought a metre long 16mm SDS masonry drill and drilled to around 3 feet deep before my drill had no more torque left and didn't appear to get to a porous level. Neighbours on the opposite side of the street in Victorian terraces with basements don't have too many problems, so I don't think it's the water table for the area.

The surface water at the back of the house goes into a combined surface and foul water sewer that runs roughly along the fence line. I don't really want to drain into that as I'd be adding to flood risk, but not sure what soakaway options I have.

Access to the back garden is along a ~1m wide passage, but it has a roughly 90 degree bend halfway, same for the neighbours gardens. Would a micro excavator make it round the bend? The back fence is onto a parking area for a block of flats, I guess I could pull the fence down for equipment access if they agreed, but it's a big block externally managed, so not easy to arrange.

I'm currently thinking of hiring a micro-excavator with operator and seeing if they can make it round the passage and then getting them to dig as deep as they can to see if we reach a porous layer, but wondered if there's something else I could do?

Any ideas gratefully received. Photos below.







Zarco

17,701 posts

208 months

Thursday 12th April 2018
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Astroturf

B17NNS

18,506 posts

246 months

Thursday 12th April 2018
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http://www.pavingexpert.com/drain16.htm

Personally I'd be running it into the drain.

Flibble

6,470 posts

180 months

Thursday 12th April 2018
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Is the concrete there to prevent contamination from the previous use rising to the top soil? Seems odd to lay out otherwise.

henrycrun

2,448 posts

239 months

Thursday 12th April 2018
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Believe me, I'd much prefer grass but - could you dig out some flowerbeds with a kango and then deck the remainder ?

Maybe split levels for the decking ?

Tigerfox

5 posts

71 months

Thursday 12th April 2018
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If you can dig a trench 12-18 inches deep the length of your garden put some 50mm plastic land drain in. You only need 1 inch of fall and connect to your surface water drain. Cover the drainage pipe with 6 inches of gravel and then backfill and that should cure it.

Spent many years driving drainage machines and the change even in a few days can be surprising.

grantone

Original Poster:

640 posts

172 months

Thursday 12th April 2018
quotequote all
Thanks for the suggestions.

I had assumed that the concrete was left over from the previous use of the site because the developer knew they would just pop topsoil over it, would it be unusual for the developer not to fully remove it? My best guess is that the location of my garden used to be hard standing or an ancillary building.

Would I still need to sort out the drainage if I went with artificial grass?

Tigerfox

5 posts

71 months

Thursday 12th April 2018
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You still need somewhere for the surface water to drain too. if you put a gravel soakaway connected to the surface water drain I think you would need a fall on the artifical grass to guide the water to the soakaway.

joestifff

778 posts

105 months

Friday 13th April 2018
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We had clay soil in our garden, water would sit much like yours. When I completely did the garden as it was also a new build I used this:

https://www.drainagesuperstore.co.uk/product/perfo...

Sat in gravel and directed to the fields and trees at the bottom of the garden, made a huge difference. If you have no where to take it to then maybe dig a large soak away and put this in:

https://www.drainagesuperstore.co.uk/product/storm...

thetapeworm

11,190 posts

238 months

Friday 13th April 2018
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Following with interest for ideas - we're in a rental currently that was supposed to be short-term but is turning out to be otherwise. It was built about 10 years ago on the site of an old mill and the garden is mainly rubble and clay.

One side of the garden is one of the old mill walls which channels water down to the bottom on a gradual fall, the owner of the house has planted a tree there and piled up clay soil which forms a dam.

At the bottom is a neighbour who appears to have installed something up against the fence line to stop water draining into their garden from ours, they have astroturf and paving.

Neighbours appear to have similar drainage issues to us but to a lesser extent as the slope appears to drain their gardens into ours to some degree, the bottom 1/3 of our lawn is currently a small lake whereas theirs look "boggy".

The bit that isn't underwater is just generally wet, even after a few dry days walking on it results in wet feet.

I was happy to just put up with it on the basis that we'd be moving soon but as that doesn't seem to be happening for a while now, and the landlord is very hands-off and unwilling to spend money, I might have to do something myself. Those soakaway crates look great but presumably I'll have to factor in draining all my neighbour's gardens too for it to be really effective, otherwise I'm replacing my water with theirs?

We also need to add a better fence, improve the lawn, plant some actual plants and make the garden somewhere worth being, seems a lot on a rental but is it worth it for a couple of years of enjoyment (noisy and annoying neighbours aside?).

Image shows boundary in orange, main issue area in blue. Also highlights we have a larger garden than our neighbours which must annoy them when it's essentially a neglected wet meadow at present and they seem to like their gardens.


xx99xx

1,892 posts

72 months

Friday 13th April 2018
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OP: grass or any vegetation on the garden will absorb a lot of that water during growing season. Not sure if you've tried that? Granted, it doesn't help much in winter but we generally use gardens less in the winter anyway and the most well drained lawns can be a bit soft in winter. Chuck a ton of sand on there as well to improve the condition of the soil. The worms should work it in to the clay for you.

Also bear in mind you'll need permission from your water company to connect to their sewer, but as you're rightly not keen on that you're probably looking at a soakaway with some buried channels to help shift any standing water.

If you can't get an excavator round there, you could always get a pneumatic drill to break up the concrete layer. Could probably get away with just drilling out a few channels, rather than digging up the whole garden.

Swervin_Mervin

4,429 posts

237 months

Friday 13th April 2018
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You need to be careful digging on a brownfield site, in the event that it has been "capped" if it's contaminated land.

Where's the site, out of interest? I "might" have half an idea of whether it was contaminated or not. It looks very similar to a new estate we lived on that was constructed around the same time.

grantone

Original Poster:

640 posts

172 months

Friday 13th April 2018
quotequote all
Swervin_Mervin said:
You need to be careful digging on a brownfield site, in the event that it has been "capped" if it's contaminated land.

Where's the site, out of interest? I "might" have half an idea of whether it was contaminated or not. It looks very similar to a new estate we lived on that was constructed around the same time.
I didn't really want to give my exact location away, but I guess it doesn't really matter. I'm on the site of the old Altrincham Ice Rink.

Swervin_Mervin

4,429 posts

237 months

Friday 13th April 2018
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Ahhh, just round the corner from where we are now, and a stone's throw from one of our favoured takeaways. The former Sharston baths was where we previously lived biggrin

Shouldn't be contaminated then AFAIK. Sounds like they've been a little lazy. I wonder what the original site spec was supposed to be because leaving large slabs of concrete around doesn't seem like the best site-wide drainage strategy!

ETA: SOunds liket he best strategy, if you can get something in there, is to dig a decent sized soakaway, as suggested above.

I did similar at our old place in Sharston but that was mainly because it was particualrly bad clay. Put a field drain running down one side and then diagonally across into a 1mx1m basic soakaway, and we never had any issues after that.



Edited by Swervin_Mervin on Friday 13th April 17:02

grantone

Original Poster:

640 posts

172 months

Friday 13th April 2018
quotequote all
xx99xx said:
OP: grass or any vegetation on the garden will absorb a lot of that water during growing season. Not sure if you've tried that? Granted, it doesn't help much in winter but we generally use gardens less in the winter anyway and the most well drained lawns can be a bit soft in winter. Chuck a ton of sand on there as well to improve the condition of the soil. The worms should work it in to the clay for you.

Also bear in mind you'll need permission from your water company to connect to their sewer, but as you're rightly not keen on that you're probably looking at a soakaway with some buried channels to help shift any standing water.

If you can't get an excavator round there, you could always get a pneumatic drill to break up the concrete layer. Could probably get away with just drilling out a few channels, rather than digging up the whole garden.
Re: vegetation. Yes, we had quite a well stocked garden before I started investigating the drainage!



I've got a local mini-excavator guy visiting on Monday to check site access. Fingers crossed.

Evanivitch

19,798 posts

121 months

Friday 13th April 2018
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Can't you take the rear fence down and come in from the car park??

I wonder if a soakaway drilled through that concrete is the best idea. Should be able to get a breaker in there and get through.

I'd also check any of the investigations when you bought the property, perhaps it was an ice rink more recently but it could have been anything before then (heavy metals for example).

grantone

Original Poster:

640 posts

172 months

Monday 16th April 2018
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A micro excavator won't fit round the corner of the passage or through the house, so will have to investigate pulling the fence down and coming through the car park of the flats at the back. Shame it's not a panel built fence as that would have been easy.

Did some more investigation on the previous uses of the site before the ice rink. Nothing in the conveyancing searches, so went looking for old maps.

http://www.old-maps.co.uk
http://www.oldmapsonline.org

What fantastic resources, I lost quite a bit of time looking at both. I've found that the ice rink was the first building on the site sometime in the late 60's or early 70's. Prior to that it was a field next to a chapel, thankfully not a graveyard, possibly part of the land retained for the leisure of the adjacent Linotype industrial village.

https://www.visitmanchester.com/things-to-see-and-...

I'm tempted to buy a Screwfix breaker and see how far I can dig while I'm trying to arrange access through the apartment car park. The local hire place 500 yards away does them for £42 per day, or £84 for a week, so man maths says buying the Screwfix one at £150 is clearly better value.

https://www.screwfix.com/p/titan-ttb280drh-15-5kg-...

Mr Pointy

11,143 posts

158 months

Tuesday 17th April 2018
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To get through that I'd have thought you're going to need something more like this:

https://www.hss.com/hire/p/heavy-duty-breaker-hilt...

Flibble

6,470 posts

180 months

Tuesday 17th April 2018
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Hirestation is a fair bit cheaper than HSS, there's one up in Trafford.
https://www.hirestation.co.uk/tool-hire/Demolition... £50 a week, you'll need a 110V converter, but they have them for £5/week too.

Croutons

9,807 posts

165 months

Tuesday 17th April 2018
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thetapeworm said:
I was happy to just put up with it on the basis that we'd be moving soon but as that doesn't seem to be happening for a while now, and the landlord is very hands-off and unwilling to spend money, I might have to do something myself. Those soakaway crates look great but presumably I'll have to factor in draining all my neighbour's gardens too for it to be really effective, otherwise I'm replacing my water with theirs?

We also need to add a better fence, improve the lawn, plant some actual plants and make the garden somewhere worth being, seems a lot on a rental but is it worth it for a couple of years of enjoyment (noisy and annoying neighbours aside?).

Image shows boundary in orange, main issue area in blue. Also highlights we have a larger garden than our neighbours which must annoy them when it's essentially a neglected wet meadow at present and they seem to like their gardens.

Thread diversion, sorry OP: You're going to spend a fortune on a property you don't own???

With a landlord who is not interested???

Seriously???

Move to another rental. They're ten a penny. Especially if the area is chock full of 10 year old houses...