Why install a septic tank with main drainage available?

[Graeme]

Near here (Aberdeenshire), a fairly rough 1930s bungalow sold a while ago, and was promptly demolished, to be replaced by a new detached house. Not a rural site as such, although a rural location, but a road of similar houses, mains drains and electricity.

Following completion of the house, a large hole was dug in the rear garden, with a huge digger. Somewhere between 2x3 to 3x4 meters (I'm nosing through the fence). The spoil was then sieved using the digger bucket, the hole lined with plastic tarpaulins, and the stones from the sieving put in the bottom. I missed what happened next, but the huge pile of sieved spoil has gone, as has the hole BUT there are two corrugated pipes protruding from the ex hole, with manhole type lids. There was a trench from the house to the hole. I cannot think what could be in the hole other than a septic tank, but why install a septic tank with mains drainage outside, or what else could it be? Not enough time elapsed to build a nuclear bunker!

[Chris Hogg]

They want to save on water rates? (Darn sarf if you have a septic tank you only pay for water used, not water disposed of, so rates about half).

But it doesn't sound like a septic tank. These days they're almost always a Klargester type thing, like a huge round-bottomed flask with a single inspection cover, although for larger properties or a tank serving several properties, larger tanks with two inspection covers can be used.

But septic tanks also need a drainage field, usually a herring-bone arrangement of pipes fanning out from the tank and buried in trenches with gravel. You make no mention of that.

Perhaps it's just a soakaway for rainwater drainage, but then why line it with tarpaulins, unless they're permeable.

[Marland]

some suggestions

The stones were put back and some concrete laid and a buried LPG tank installed while you were not there.

Rainwater storage and the trench is for a pipe to carry water from the gutters.

How high is the water table? It there is now a pit full of stones like an oversize soak away that will fill from the groundwater could it be a source for a heatpump rather than laying out yards of pipe or drilling a borehole.

GH

[Clive Arthur]

Could it be for a ground source heat pump? A complete guess, I know little of these.

Cheers

[spuorgelgoog]

No mains drainage = cheaper water/sewerage bill.

Owain

[Jim GM4DHJ ...]

On 22/09/2019 11:38, Graeme wrote:ange

if it is a Klargester type septic tank and it sounds like it they won't be allowed to use it if mains foul drainage is close bye .....strange ...must be something else......

[Fredxx]

It's possible that the bungalow run-off went into the local sewer rather than a storm drain.

The new building probably required a new soakaway to be built. Certainly rules don't permit surface water to enter the sewer system unless the soil is impervious or there is a high water table.

I thought septic tanks required a more distributed outflow? But given you never saw a tank, or a hole being dug for one suggests this was done to make a soakaway.

[Tim+]

Is it not more likely to just be a large soakaway? New house builds probably aren?t allowed to put rainwater into the sewers (which the old house almost certainly did).

Tim

[Jim GM4DHJ ...]

more a herringbone outfall is required for a septic tank.....

[Jim GM4DHJ ...]

could be suds attenuation of storm water ....

[The Natural Philosopher]

soakaway

[Graeme]

In message [e-mail], Chris Hogg [e-mail] writes

Looking at the link supplied by Chris, the bits sticking out of the ground look exactly like the illustration of a Klargester Gamma (top row, 4th from right) although there are two of them, both black.

I don't walk the dog the same walk every day, so missed the bit between a large hole and all covered, but I seriously doubt there was time for a drainage field to be constructed, and not enough space anyway. I think a soakaway for rainwater sounds promising, and will look for other clues when next going past - but would a soakaway have those two corrugated bits above ground level?

[Steve Walker]

Could it be the reverse and be part of a rainwater/grey water collection system?

SteveW

[Chris Hogg]

Something like this perhaps?

are commonly constructed with crates these days, a bit like milk crates. The bits sticking up are inspection covers, although what there is to inspect, I don't know.

[Martin Brown]

OK to answer the question the policy in Belgium is that all houses that can are required to have a septic tank so that they only discharge liquid effluent into the drains. Saves them having to dig out fat bergs.

Customer has to pay to have their own septic tank pumped out if they are careless about what they throw down the toilet. The junk never makes it into the main sewer saving a lot of hassle for the authorities.

It could also be a grey water tank for collecting rainwater off the roof and drive. Our house in Belgium also had that refinement and I know a few new builds where large tank rainwater collection has been added.

[The Natural Philosopher]

to see when the soakaway is clogged with silt

[Graeme]

In message [e-mail], Chris Hogg [e-mail] writes

Chris, brilliant. Whilst I have no idea what is below ground level, the two parts above ground look exactly like those visible in the garden.

So, the answer seems to be, it is a soakaway for rainwater, installed because, now being a new build, the rainwater cannot enter the general foul water sewer.

Thanks all!

[FMurtz]

Why not ask the builder or owner?

[Brian Gaff]

Many years ago I had an extra downpipe put on my house at the front when new guttering was fitted as there are only down pipes into the sewer at the ends of a terrace of four. The problem was the rain came over the top on my head at the front door,. Its been there for many years and its loved by a large flowering camelia planted there. A while back a council bloke comes around and looks at it and says, that's not legal mate, it if you were fitting it today that plant would come out and you would need a proper soak away or pipe to the sewers there. I ignored him of course and nothing came of it, and the shrub has continued to flourish!

Brian

[Brian Gaff]

Well, around my way new builds do have their rain going into gulleys which run into the sewer via a drain, so although not connected the intention ii so obviously that they should go that way. I wonder if this is worrying the original poster, why not just be nosey and ask? I think I would. Brian