Mapping drains

[daven1986]

Hi all,

Wasn't sure if this should go here or in building, but it is here now!

I want to build over an inspection chamber but that means moving it. Now Thames Water don't have accurate maps of the main sewer which runs somewhere in my garden! So before I get build over permission I want to get the drains mapped so I know exactly where they run.

A company I spoke to mentioned that if there is a running trap then they won't be able to do a proper cctv survey and will only be able to produce rough maps as their cameras won't fit through. I had a look inside my inspection chamber, and aside from needing a bit of a clean I noticed some water at the end, which looks like a trap of some kind, before it goes off to the main sewer. Is this a running trap or is it normal?

Any way I can ensure there is no running trap before I commission a survey?

Thanks

Daven

 

[polesapart]

Old style interceptor traps (rare!) normally found only on outlet of last manhole before public sewer.

General old skool rule; no junctions,or change of gradient or direction of underground drainage except at inspection chamber.

If this rule has been followed mapping can be easy, so long as no barsteward has built over or hidden manhole covers.

 

[daven1986]

Thanks. Unfortunately from googling interceptor traps, I think this is what I have does that mean mapping cannot be done? All I need really is to find out where the main sewer runs across my garden - I'd guess shoving a rod down there until it hits the sewer pipe would do - but I don't want to do this myself!

 

[polesapart]

Main sewer "should" be running in a straight line between its manholes.

 

[daven1986]

So there aren't any manholes in the garden (except for my inspection chamber). I believe (and this is what Thames Water thinks too) that the sewer runs like this:

-----------------
|
________x____
| my house |

Where "x" is the inspection chamber just off the back wall of my house, with a run down to the main sewer line that runs across all gardens.

Thanks

Daven

 

[Jackrae]

You could tried dowsing for the drains or get someone who does. Sceptics consider is hokumpokum but it can work as many will vouch. My wife managed to trace out water mains feed line when we had a leak using nothing but a bent pair of wire rods. When the water board eventually came they asked how we'd managed to mark the track so accurately.

 

[Hugh Jaleak]

Even if there is an interceptor, a camera should be able to be put through the rodding eye to look into the drain beyond. Nothing is impossible. Sonar tracing using rods is another option.

 

[daven1986]

Thanks Hugh. I'll give a few companies a call and see what they can offer.

Thanks for us suggestions,
Daven

 

[Agile]

Most intercepters have a bypass rodding eye above which used to have a china plug ( rarely still there ). Sometimes it has fallen into the trap and blocked it.

If you can access with a rod then you can use a Cable Avoidance Tool together with a generator. The generator is used to power a wire drawn into the drain on rods and the CAT used to trace it from above ground.

You can build over existing drains by encasing them in concrete. Inspection chambers can be retained and fitted with a new bolt down sealed lid.

Tony

 

[daven1986]

Thanks Tony, now you mention the location I think I noticed the rodding eye. I'll have a word with some contractors and get this mapped out!

Cheers

 

[Agile]

Not all contractors are that clued up technically at tracing drains!