Foul water drain issue

[WJMarlow]

Hi I have a foul water drainage system which has been laid by the house builder
There was a bad smell coming from it into the house so had a CCTV survey which demonstrates stagnant water in the drain
Had concerns about whether fall of the drain was correct so I viewed the house builder's plan for the system with a view to laser level checking the fall according to the plan.
But the plan shows a completely different layout of drains to what is in the ground so the heights shown on the plan are completely meaningless.

The house builder is saying that it is normal for there to be stagnant water in the drain - is this acceptable? - I would have thought that if the drains were laid with a consistent fall then the water should just drain away

Is this likely to be an issue with the fall being incorrect from the start or with subsidence causing part of the drain to sag?

 

[Old Account]

Obviously, every single drain should have a reasonable fall so the water or waste will not stagnant. If it's stagnant then there is an installation problem.

Does the water back up ?

The only waste water which will stay would be the water in the siphon or trap so the bad smell wont come back.

Where does the smell come from ? You will need to check that if you flush a toilet that it doesn't suck the other traps empty otherwise bad smell coming through those traps.

 

[ShaunCorbs]

as above but how much water are we talking about if its only a wee bit and doesnt go very far i would say its fine but if its something like 1/4 full somethings wrong

 

[WJMarlow]

Hi Matchless.plumb
Water doesn't back up - just pools in the short section of drain outside the house - the same smell in the house as when the drain cover was opened
Only one toilet and one sink are connected to that drain - it's possible that the sink trap is getting sucked empty by the toilet flush but am going to fit an anti-vac device to try to stop this from happening

But my concerns are with the drain structure - another connecting drain has previously collapsed and now the water is pooling in this one - the anti-vac will solve the smell
but you've confirmed my suspicions that there is an installation issue and it is not acceptable for water to be pooling in it thanks - ill go back to the house builder with this

 

[WJMarlow]

Hi ShaunCorbs
CCTV was a bit grainy but the section of drain is about 4m long and about 3m of it had about 1-2cm depth
The CCTV guys said it was an abnormal amount but they were fairly non-committal to me since the house-builder had commissioned their survey
They said it looked like it was blocked, but we've subsequently ruled this out
So I'm fairly sure that the amount of water pooled there is more than would be normally seen
Thanks!

 

[ShaunCorbs]

Hi ShaunCorbs
CCTV was a bit grainy but the section of drain is about 4m long and about 3m of it had about 1-2cm depth
The CCTV guys said it was an abnormal amount but they were fairly non-committal to me since the house-builder had commissioned their survey
They said it looked like it was blocked, but we've subsequently ruled this out
So I'm fairly sure that the amount of water pooled there is more than would be normally seen
Thanks!

yea i would say as well somethings wrong maybe that section has just dropped slightly since it was installed