Drainage issues

smokybacon · Jun 9, 2012

H, I am a surveyor with no real draiange experieicne and I would be grateful if anone had comments to make on the following.

For years, a three storey building has had foul smells. The waste wash basin traps were accumulating a black sludge within three month of being cleaned out. Soaps have been changed and we have renewed the traps to try and alleviate the smell. Is there anything that would cause the black sludge to appear?

In a ground floor office they have been experiencing random methane smells and when I was recently there the methane was intermittently very strong. All the drainage has been checked using a camera and it is fine, albeit it is laid to a near level gradient and is jet washed every quarter. However, according to plans there is a redundant pipe below the building. Could this really be causing intermittent smells in the building due to being backed up- the building is 9 years old. We are near to a tidal estuary and I am wondering if water levels could be anything to do with it.

Finally, if the buiding's drains are not defective (other than partially holding silt) I cannot see why this would be a cause of any smells coming into the building other than traps being sucked out - Is this right?

Any comments would be useful. I can attach a plan of the drainage.

SimonG · Jun 9, 2012

I would be looking at how the soil system is vented.

jtsplumbing · Jun 9, 2012

Do the drains run direct into estuary ? Meathane leavels a bit worrying are they being moniitored ? as any of the gunk in pipes and traps been analysed to find out what it is ?

stevetheplumber · Jun 9, 2012

im with simon drains that are properly vented have virtually no smell unlike new estates with durgos that make their drains stink

smokybacon · Jun 9, 2012

SimonG said:
I would be looking at how the soil system is vented.

Is this because, foul water may discharge from drains easier. Or would this help with smells in any way?

Mike Jackson · Jun 9, 2012

If the system's not vented properly traps will be pulled out at lower levels and smells will come back up.

smokybacon · Jun 9, 2012

The 'gunk' has not been tested. The 'methane' smell was like raw cabbage, but there is only one drain below this area which is a capped drain with a rest bend - CCTV survey shows no probems.

SimonG · Jun 9, 2012

smokybacon said:
Is this because, foul water may discharge from drains easier. Or would this help with smells in any way?

As Mike said, poor ventilation to soil systems will result in traps being pulled out and smells in.

Bernie2 · Jun 9, 2012

Hmm!

Not sure. But some thought?
Sometimes drains near tidal estuaries where designed to flood and be washed out at high tide. Using say an anti flood trap before entering a main sewer may stop the flood cleaning action happening. And as you say, a change in tidal range may affect it.

If for instance the main sewer is designed to be flood cleaned by the tide and building work or weather or tidal flood barriers have been built perhaps its not happening.

But then is the drain getting enough water into it to swill the substances out?

There is always I suppose going to be the question with the many water saving devise we now use of the drains not cleaning themselves. The methane smell as you know is usually given off by rotting vegetation or soil discharge and if it is not getting away one has to ask if there is enough water entering the system or enough fall on the drain to wash it away?
The black slimy gunge is quite common in drains, but doesn't usually build up so fast, which seems to make one wonder if it is getting washed away.

smokybacon · Jun 9, 2012

So could the obsolete drian below the building be getting backed up from the main sewer? I know we need to dig down and check the drain.

If drains are slightly backing up I thought that the smells would be vented and therefore no smells would enter the building - or am I wrong in this thinking?

Bernie2 · Jun 9, 2012

Theoretically a drainage system should have through ventilation so fresh air can flow through the system. Usually the main sewer is vented somewhere and then the branch to the property and the property drains themselves are then vented giving a through draft. Unfortunately on some systems near rivers you have to seal the property drains from the sewer to avoid flooding. So at high tide the anti flood valve shuts and any air circulation stops. But of course on a properly designed system with all the correct trap seal depths and drains seals done. It should not really smell.

The problem is you do not really know what the old drain is or does or whether tides are causing back flow, perhaps a cause of to much water rather than not enough.