THAMES WATER will 'imminently' submit plans to the government for two major sewer tunnels in east and west London that would involve building diaphragm walls up to 80m underground.
The utility company told GE it was preparing to present the plans to Defra (Department of the Environment Food and Rural Affairs) for the tunnels, which would stop 20M.m 3 of waste water overowing into the Thames each year.
Thames Water has already presented plans for a 34km, 7.2m diameter sewer from a pumping station in Hammersmith in west London to a treatment works at Beckton in east London.
'We went to Defra with a proposition for a £1.7bn tunnel, ' a Thames Water spokeswoman told GE. 'They have asked us to come back to them with proposals that are not so costly.'
Under the new proposals, one tunnel would take storm water from Hammersmith to Battersea in south London where it will be treated or stored. The second would carry waste water from Abbey Mills in Stratford to a sewage treatment works that is being upgraded at Beckton.
Ministers are understood to be ready to approve the Abbey MillsBeckton link rst. The tunnel, which would cost between £200M-300M, would improve water quality in the Thames and River Lea in time for the 2012 Olympics.
Detailed design work and procurement would take at least 12 months before the scheme could start on site. A feasibility study has already been worked up by a team for Thames Water led by consultant Faber Maunsell and including contractor Amec and tunnelling specialist Lovat.
The tunnel between Abbey Mills and Beckton would run at a gradient beneath the Thames, reaching a depth of 80m at Beckton to allow for gravity drainage. It would be built using TBMs and diaphragm walls.
Slurry machines would be used for the tunnelling at up to 80m deep.
'It's not normal practice to do diaphragm walls this deep but it has been done before, ' an insider on the project told GE. 'There will be a lot of discussion about the methods used but this is thought at the moment to be the most likely technique.'
One of the biggest challenges would be connecting the new tunnel with combined station over ow (CSO) pipes that are currently discharging waste water into the Thames, he added.
'The CSOs are at very restricted locations where there is a lot of traf c. They are live sewer connections so it will be very difcult, ' he said.