Need to determine sewer depth in my back garden - Sewer depth

[Kevin10]

Hello all & Hope you all had a merry Christmas.

I am building a rear extension which has currently gone in for planning permission.

I have to submit to Thames water an application for build over agreement as the extension protrudes 3m from the rear wall while the sewer line is roughly 2m away in my rear garden running parallell to my street. See existing layout:

http://picasaweb.google.co.uk/lh....ectlink

I am advised that in my application to Thames water, i need to detail the depth of the sewer line and it's position and show the mitigations will be in place to prevent damage to their sewer e.g. lintel.

I have obtained an asset search from Property Insight but it unfortunately doesn't give the depth of the sewer line, only the depth of manholes presumably in the main street? .. I have scanned an uploaded here (my house is 76 Eswyn Road) :

http://picasaweb.google.co.uk/lh....ectlink

http://picasaweb.google.co.uk/lh....ectlink

http://picasaweb.google.co.uk/lh....ectlink

I have consulted a local plumber who says that the sewer in my area is 10 ft deep. What confuses me is that the invert level in my inspection chamber is only around 800mm which means that the sewer line must drop 6 feet in the space of 3 feet! (I am told it is not normal for levels to change so drastically over small distances). See existing layout for position of inspection chamber relative to sewer line.

http://picasaweb.google.co.uk/lh....ectlink

I have done alot of reading on the matter and recall reading that the sewer level is more or less the same as the invert level in the inspection chamber.

This may be obvious to someone, if so, I would greatly appreciate advice.

Cheers.

[Dave_L]

Dig down and expose sewer? Then there it is in black and white, no guessing or assuming.

[Kevin10]

thanks, I was going to, but when the local tradesman suggested it was 10 feet down, the prospect of doing that was quickly un-appealing..

Was hoping that there were obvious tell-tale signs. For example by reading the map that insight sent back, i am at the start of the sewer line, which suggests that it shouldn't be too deep... ?



My objective at the mo is to get a good enough picture to submit an application to thames water. When the contractors break ground it *should* become clear.

[flowjoe]

Put that shovel away kevin.

This is standard practice for planning permission with many of the water companies requiring proof of depth and the distance of the sewer from your property.

Any decent drainage contractor will have a sonar drain tracer which the send into the sewer, it sends a signal up to ground level showing the line of the drain and the depth.

It just depends on the size of the sewer and the distance from the nearest manhole which method they use to get the tracer into the sewer.

HTH

[Kevin10]

thanks for that. I think i'll do just that and give some drainage contractors a call.

Can you recommend any? The only one i know of is Dynorod and i know they charge a fortune.

kevin.

[flowjoe]

There`s no need for that kind of language, using the `D` word on the forum.

I will PM you a couple of London contractors i know, they will need to know the distance from the nearest inspection chamber on the sewer run, if its in a highway or not and roughly the sewer size.

If its not a great distance they can push the equipment in place, if not they may have to use a crawler system camera to piggy back the sonar into place.

[Kevin10]

lol ... cheers for that flowjoe. You had me for a second... Look forward to your PM.

I'm located in Wandsworth SW17 area by the way.

[flowjoe]

Details Sent

[Kevin10]

thanks, PM received, will give them a call tomorrow.

[seanandruby]

Are you sure it is'nt a back drop into the manhole? There will be your pipe into the channel , then up the wall of the manhole there will be another pipe coming in ( might be bunged, or unbunged ) to allow maintenance on the pipeline.

[lutonlagerlout]

anglia water made us divert a main run around the extension rather than lintel over it £££
it all depends whether it is a private or public sewer apparently
other than that you normally have to go 200mm + below the pipe for the foundation depth
LLL

[flowjoe]

LLL

You will recall i put a post up last month regarding the water companies taking over all shared drainage from April 2011, this means that all shared drainage will be a public sewer.

Can you imagine the grief this will inflict on homeowners and builders trying to put up the simplest of extensions, not to mention the added cost of investigating/locating the sewer and implementing the exagerated design recommended for the foundations.

Stealth Tax !!!!! Sign the petition peeps if you havn`t already

[Kevin10]

Are you sure it is'nt a back drop into the manhole? There will be your pipe into the channel , then up the wall of the manhole there will be another pipe coming in ( might be bunged, or unbunged ) to allow maintenance on the pipeline.

amazing that you should say that. See picture of the inspection chamber.

http://picasaweb.google.co.uk/lh....ectlink

WHat does this mean? What is a backdrop into the manhole? I'm not too savvy with drainage, find myself learning a little more everytime.

just called the drainage contractors that Dave supplied, unfortunately one's not back till the new year and the other doesn't have the kit to do it. He advised to just use the invert level of the chamber...

[flowjoe]

Kevin

That is an interceptor trap on the outlet of the chamber, the pipework could then pass through a dropshaft before connecting into the sewer.

A drain camera inspection would tell you if the sewer is roughly the same depth as your manhole invert, if it does pass through a drop shaft its an easy enough job to calculate the depth of the sewer by the amount of camera rod you have pushed into the system from the manhole.

[lutonlagerlout]

the cursed interceptors,biggest fail ever from Edwardian plumbing
the bottom line is where ever the lowest point of the run is,your foundations will have to be deeper than that and if its 10 FT deep that is going to be costly
LLL