[Closed] Soakaway crate for black & grey water. How big ?

I have a feeling that if you need to drain foul water into it then you'll need to incorporate some form of treatment/filtering and get it approved by Building Control?

EDIT: If the above includes sewerage then you'd need a proper cess-pit surely?

No way can you discharge a toilet into a soakaway.

Take care over this; we are building a new factory handling chemicals and it took us 18 months to get Environmental approval because the local authority [s]wanted to prove they were important[/s] were worried about runoff from the factory entering the adjacent brook. We had to do permeability tests on the ground (alluvial gravel so approved) then dig a hole the size of an olympic swimming pool, line it with the membrane then fill it with those crates then cover it over. They are very twitchy about this kind of thing at the moment. Make sure you get the right approvals or at least get the calculations right.

Whoa - you'll need treatment, eg septic tank, then a soakaway or drainage field for the treated liquid as a bare minimum. If you are over an aquifer, then you may need a more elaborate treatment works.

Please check on the EA website/ building regs approved doc H.

After all that, then a big hole for the soakaway with 40mm stone will last longer than the crate and geotextile systems. The geotextile will block before a 40mm stone based system will clog.

Not a good idea IMO to put foul into a new style soakaway, asking for future problems let alone what Building Control would say

Depending on ground classification you will need a treatment plant like a Klargester before the soakaway.

Whilst obviously a manufacturer, this lot gives a guide on all the options, all subject to what building control and the Environment Agency will accept for your area.

http://www.crystaltanks.com/septic_tank_crystal.html

Are you utterly and totally sure about black and grey in a soakaway? Sounds unpleasant and downright illegal.
What you have pictured is in no way suitable for black or grey water without upstream treatment.

I should have mentioned it's the overflow from a septic tank, not direct from the toilet.
It's a wooden bungalow in the Wyre Forest. There are hundreds of them here, originally built as holiday homes.
There are all sorts of widespread unusual practices around here which wouldn't meet normal building regulations.
I don't think anyone has got a septic tank big enough to capture all the water as well. Allowing it to overflow in to a soakaway is probably the most common arrangement.

Well you did only miss out a VERY important detail in your original post.

The Environment Agency should be involved in the design of any soakaway to ensure the soil is permeable enough. If it isn't, you might make it worse and no number of plastic crates will help with that.
I know you don't want that answer, but the fines can be pretty big.

Aha - we can untwist our knickers now.
The septic tank does 'treat' the liquid and cleaner water is drawn off to the soakaway. You'll no doubt need a pump out of the solids and then a new soakaway if the soakaway capacity is compromised. Sometimes a tank that's overfull can block the soakaway. A pump-out and inspection will tell you what needs doing. Maybe a jetting of the soakaway from inside the tank is all that's needed to shift the matter blocking the soakaway entrance.

All subject to LA/EA approval of course as there are no short-cuts for this sort of thing if you are installing new off-mains drainage.

The void ratio of those crates is a lot higher than a pit filled with stone. So to get the same volume you should measure the volume of the original pit, ignore the stone fill then take about 30% of the volume of the empty pit. That will give you the volume you require.

That crate assuming the dimensions are 1000mm(L)x500mm(W)x400mm(depth) gives you 0.2m3. You will need as many of the crates that will give you the same volume as the original soakaway, maybe add 1 or 2 extra for good measure.

And what they ^^^ said about Local authority/EA approval or there might be a local land drainage/internal drainage board that deals with this stuff.

Yes, I should have explained better, I just assumed that when I said water, everyone would know what I meant. I don't think anyone would expect toilet waste, solids and all, to disappear through a soakaway.

Anyway, back to the original question;
Supposing I was living somewhere where the local authority, planning department, building inspectors etc, don't appear to take any interest in what goes on, and it was entirely up to me how I got rid of the water, how many of those crates would I need for three people ?

how big is the original pit? length, width and depth?

Its not just comparable volume though. Permeability considerations too, as the crates have less external surface area per volume held than stone. Also there will be some depths where the soil drains better.

you really need to check whether you are in a SPZ or not.

yeah so get the volume of the original pit add a few crates to increase the volume a bit, it'll be reet.

Obviously if i was designing it at work i would want the permeability factor of the ground and contributing area, but if it worked previously it'll work again, it's only taking a 2 bedroom (wild assumption there) bungalow.

he's already discharging to ground anyway so he's not actually changing anything. If it was an SPZ the local water company would have stopped them all soaking away.

Any rule of thumb volumes will be for piped systems and would therefore assumes the tank is empty at the start of every day. thsi means the ground needs to be permeable enough to achieve an empty tank (be very careful in digging the pit to ensure the ground does not get compacted as this can ruin any inherent permability). This also may not be achievable if the groundwater table is shallow, so this will need to be confirmed first. And as above any grey/black water over an aquifer is seriously bad news from a pollution persepctive.

It's also bad news if any of the rainwater from the roof/driveway/patio is going to the tank, this will cause massive issues for both the tank and the pollution of any soakaway you install

Ths crates design shows there should be a minimum clean stone 150mm band to all sides which is vitally important for permeability and structural support.

I would suggest you talk to a building inspector, they will probably be able to tell you if your approach would be acceptable with very little trouble and prevent you being subjected to their wrath. Remember if it has piped mains, the water board will be aware the water is going somewhere and may decide to take a look one day.

not sure this is any use but i think it would be worth your while getting a building inspector out or a local civils/drainage engineer (a proper one, not a plumber) to just take a look.

Not in a SPZ as far as the Wyre forest is concerned, that is just an overview as I dont know where MTG's specific location is.

So. The original system was probably built on a small capacity as it was built as a holiday home ie not 52 week occupancy. You've now got full time occupancy and probably more water used than when built. I'd say you would need to size up, and the comments above with regard to surface area support that anyway.