National Grid Bore Holes near Walthamstow Marsh

National Grid 
Ground Investigation Works at Leyton and Walthamstow Marshes
National Grid owns and manages the grids to which many different energy sources are
connected.  In Britain it runs the systems that deliver gas and electricity across the entire
county, which means it holds a vital position at the centre of the energy system – National
Grid joins everything up.
In London electricity consumption is rising each year and it is National Grid’s responsibility to
ensure there is sufficient transmission infrastructure available to support the Capital’s future
energy demand.
In February 2011, as part if it’s continued investment, National Grid embarked upon a sevenyear project to rewire the capital via deep underground tunnels, in order to meet increasing
electricity demand and help London access the renewable energy of the future.
In total 32km of tunnels are being constructed between 20m and 60m deep below the road
network. The tunnels will carry high voltage (400kV) electricity cables and connect existing
substations at the following locations:
• Hackney
• St John’s Wood
• Willesden
• Wimbledon
By housing the cables in deep underground tunnels we will significantly reduce disruption to
the local area as we are able to lay the cables and carry out maintenance work without
digging up the road network.
Intermediate tunnel access shafts are required along the tunnel route.  The two tunnel boring
machines which are being used to dig the tunnel will connect these points as they progress
along the route.  Headhouse buildings will then be constructed above the tunnel shafts.
These are needed to ensure the safety of our workforce during construction, provide access
to the tunnel for maintenance work, and store ventilation equipment which is required to cool
the electricity cables and regulate the temperature inside the tunnel.
As a complex engineering project, it is vital that we have a detailed understanding of the
ground conditions we will be tunnelling through, and therefore a series of boreholes are
being completed along the tunnel route to ensure we have accurate and reliable ground
condition information.
The borehole investigations planned within Leyton and Walthamstow Marshes form part of
this work and will take approximately 26 days to complete.  The borehole will be
approximately 30cm wide and 50m deep, and the small surrounding area required to
complete the work will be temporarily secured using metal fencing.  Once the work has been
completed National Grid will place a small cover on the surface and will visit occasionally.
There will be no remaining above ground presence on the land.
For further information about the London Power Tunnels project please visit
www.londonpowertunnels.co.uk
Email: nationalgrid@londonpowertunnels.co.uk
Freephone: 0800 783 2855