Water Boost For Brighton
19 July 2010
4D, the joint venture that combines Costain with United
Utilities and MWH, is helping to deliver a £225million
environmental improvement scheme to bring cleaner seas to
Sussex.
At present the wastewater receives only basic treatment before
being released through an outfall pipe 1.8km off the south
coast.
Tunnelling underway
By 2012, a combination of 11km of tunnel, three new pumping
stations and a wastewater treatment works at Peacehaven, east of
Brighton, will see the wastewater fully treated and then dispersed
at sea through a new 2.5km pipeline.
Two 2.44-metre diameter tunnel-boring machines (TBMs) - one
ceremonially lowered into one of the 16 shafts that are being
excavated along the route on 29 June - have just started their
work, which will continue 24 hours a day until next January.
"We're looking to achieve between 10 and 40 metres a day in full
production," says Craig Reade, Costain's Project Manager
(Infrastructure) on the job. "The geology is essentially chalk,
with some flint inclusions and possibly some seams, but nothing too
challenging." The TBMs will create nine kilometres of tunnels, with
pipejacks driving a further two kilometres and a huge barge, Nordic
Giant, having already dug the seabed trench into which the new
outfall will be placed.
The largest shaft, at Marine Drive on the eastern edge of
Brighton, is 46m deep and 17.5m in diameter. When complete, it will
house one of the scheme's three pumping stations; the shaft will be
divided into 'wet' and 'dry' halves by a central vertical wall.
Wastewater will fill the wet half, which will be lifted by pumps in
the dry section and travel by gravity towards another pumping
station at Portobello, then onwards to the waste water treatment
works at Peacehaven, 11km east of the town.
The tunnel will intercept several existing sewers and add their
contents to the eastwards flow.
The Marine Drive pumping station will be covered with a
distinctive architectural zinc-domed 'landmark structure' with
traditional stone walls. The only sign of the shafts will be
manhole covers.
Camouflaging the treatment works
How to hide a 39-hectare, 4.5km-perimeter site containing a
state-of-the-art wastewater treatment works? Moving 800,000m³ of
earth to create a huge hollow into which the plant can be placed,
carefully shaping earthworks around it, then covering most of it
with a grass roof the size of almost three football pitches, is one
way of doing it.
The aim is to retain the views across the South Downs. When
complete, the works will be hidden in a large excavation within the
re-profiled landscape.
The main complexity of the project is its sheer scale, says
Project Manager (Treatment Works) Graham Sugrue. As well as the
vast earthworks, the treatment works will use 26,000m³ of concrete,
with 39,000m³ employed across the project as a whole.
"This is very much state-of-the-art. It's the biggest plant of
its type," he says. The treatment works will include a £6.5million
odour control plant and the arriving wastewater will go through a
three-stage treatment process.
After having debris, grit and grease removed, primary treatment
will remove solid waste in four huge settling tanks. The resulting
liquid will then be passed through a deep bed of polystyrene beads
in 10 concrete cells. Bacteria will stick to these beads, which
will periodically undergo a 'backwash' process to clean them.
The resulting clean water will then be piped out to sea. The
solid waste removed during the treatment process forms a sewage
sludge. This is treated so it can be safely used as an organic soil
conditioner.
Community aspects
There are significant local sensitivities around this scheme,
especially bearing in mind the planning process for this scheme
begun in 1993, went through two public enquiries and a judicial
review before planning permission was finally granted in 2008, says
Sugrue.
This has led to a major community relations programme since
Costain moved onsite last August. An exhibition centre for the
project has been set up and Community Relations Manager James York
holds monthly meetings with residents.
Local schools have been visited, with pupils at one, St
Margaret's, being asked to suggest names for one of the TBMs.
'Alice' was the winning contender. Alice in Wonderland author Lewis
Carroll came up with the idea of Alice going down a rabbit hole
after discovering a narrow passage while visiting a relative in
Brighton; the TBM is similarly going underground.
The site employs strict noise and access conditions, a
roadsweeping vehicle is employed virtually permanently to keep
local roads free of mud and dust monitors are placed around the
site. Waste generated by the earthworks at Peacehaven must be
retained on site.
Pictured top right: As tunnel boring machine Alice is
prepared for lowering into position, Brighton Project Director Phil
Risbridger (left) welcomes Jon Gilbert, Deputy Headmaster of St
Margaret's Primary School, Rottingdean, one of whose pupils chose
the TBM's name. Julian Smith, Southern Water's Project Manager
(centre) was on hand for the ceremony.
Pictured bottom right: Tunnel boring machine Alice sees
daylight for the last time for several months as it is eased into
position at the foot of the Ovingdean shaft, ready to begin
work.