Report after my meeting with Andrew Hagger, Thames Water wastewater engineer for West Berkshire – Judith Bunting.
We all know that groundwater conditions, last winter, were extraordinary. What I wanted to find out from Andrew, was why so much groundwater got into Thames Water‘s sewage system, that foulwater spewed back out of manhole covers and interior fittings. People suffered these issues across West Berks, from Lambourn and East Garston to East Ilsley and Compton, taking in significant sections of Newbury, notably Northcroft Lane and Shaw, along the way.
Laying larger sewers is not the answer. Foulwater pipes are, perhaps, surprisingly narrow (6″ – 9″ diameter), but normal sewage flow is surprisingly low volume. 1,000 homes produces, on average, a flow of just 1 litre per second. (Apparently we can be relied upon to flush in rotation.) Standard pipes are big enough for the job, so long as only waste is flowing through. The problems come when the system is flooded with groundwater.
When this happens, we must be clear: It is the system that’s at fault, not the ground water.
If the sewage system is functioning properly, our ground should be able to flood all around the pipes, every day of the year, with no adverse consequence. We deserve to be secure in the knowledge that we will never see sewage in the streets or in our gardens. We should be confident, in twenty first century Britain, that we can flush, even when it rains.
I am pleased to say, that Thames Water now seem to accept the fact that their pipes should not experience ingress of ground water however wet it gets.
With all this in mind, my chief question to Andrew Haggar today was the same as has been asked by many people I met at the time:
- How is groundwater getting into your system?
- What you doing to stop it happening?
These may seem blindingly obvious questions, but I met people with infiltration problems in this area, in the late nineteen eighties. It beggars belief that the same problems are still happening, today.
How does the water get in?
Being an engineer, Andrew gave a satisfyingly clear answers – he was willing to put a few figures on it, as well. Water gets into the foul water system in 3 ways:
- 20% gets in through cracks in the pipe and leaking joints
- 70% gets in through inundation through manhole covers, through vents, and through the walls of unsealed inspection chambers.
- 10% is put into the system by members of the public, seeking to get rid of floodwaters. People do not always realise that ifthey pour their floodwater into the foul-water drain, their neighbours may find foul-water pouring out of their loo and on totheir floor.
You will be able to get detailed reports on Thames Water‘s works, in your area, from the relevant flood forums, in due course. For now I can report the following:
- In Lambourn: relining will begin very shortly. The Council is negotiating re traffic management during the works.
- In Eastbury: the public sewers were relined ~2004. This process involved pushing a Neoprene ‘sock’ down the sewers, which was then cured into place with a chemical gel. The effect was a fresh, non-stick sewers, with no cracks.
- In East Garston: relining work, ~2004, began at the bottom of the village, working up the valley from the pumping station.
- In East Ilsley: The camera inspection of the village pipes, promised at East Ilsley’s Parish Council meeting, has now finished. Pipes were examined from West Ilsley, across the fields and down to the East Ilsley pumping station. These pictures are now being reviewed, to locate defects.
- In Compton: key manholes are begin sealed. I alerted Andrew Hagger to the ingress of water through the walls of the inspectionchamber, on Horn Lane, as reported to me by resident, Ian Hickling. Andrew has taken note, and will look into the
possibility of sealing this chamber. This is done by injecting resin into the walls.
- The aim is for work in both Lambourn and Pang Valleys to be completed by October 2014.
- In Newbury: Thames Water were somewhat surprised to hear about foul water egress in Shaw and the Northcroft Lane area. I was glad to share your experiences and my photos.
Manhole covers and inspection chambers are particular issue. Vents are required to allow the inevitable gases to escape from the system, but Thames now seems to be taking a pragmatic view to this, however, which pleases me: They are sealing the vents on low lying manhole covers, and leaving them open on manhole in higher ground.
Perhaps surprisingly, water companies have no right to object to any planning application – they are not statutory planning authorities. They do try to make it clear when development may cause a problem. If a development is large, new sewers will be built. Brownfield developments, it seems, can actually improve local sewage flow, because their use often involves reopening old, closed, sections of foul-water pipe.
Note: If you have photos of foul-water problems suffered during winter 2013/2014, send the to me email@example.com and I will send them on to Thames Water.