Two boreholes were sunk on the site in 1998 although currently only one is needed to satisfy demand. This has an overall depth of 75 m, and is lined with a 200 mm diameter steel tube driven into the underlying chalk aquifer. Tests showed that the yield from this borehole was approximately 40 m3/h, compared to the London average of 8 m3/h, and that it was of potable mineral water quality standards.
As a precaution the water is filtered to remove chalk particles before undergoing ultraviolet treatment and passing through a sand filter to remove excessive iron oxide. A spine main has been laid throughout the park's one-mile length for the purpose of distribution. Interestingly the temperature of the extracted water is around 12°C opening up the possibility of using it for cooling applications.
Potential uses for the water aren't just confined to the park. An adjacent site is currently undergoing redevelopment to provide housing for low-income families under the New Deal scheme and this will require a new water connection. The proximity of this development underlined the possibility for using water from the park's borehole to supply the housing estate, the yield of which was capable of supplying 6000 people as a domestic supply.
The opportunity led to the creation of a potentially highly profitable business plan for the private/public client while providing the housing estate with water at a lower cost than the local water company.
The Environment Agency have granted an extraction license for the water to be used in the park and for the housing supply, however the scheme to supply the residential estate has yet to come off. The size of the park and the urban regeneration taking place in the area mean there will probably be other water supplying opportunities in the future.
The Mile End park project was however able to demonstrate the possibilities for achieving the Local Agenda 21 policy of sustainable development. This included dewatering the aquifer which would help alleviate the environmental impact of the rising water table, the rewards from selling the water and community benefits by diverting expenditure to better facilities.
Rising groundwater
The problem of London's rising water table is well documented. London sits on 10 m of silty deposits, which rest on 30-50 m of London clay. Beneath the clay lies a chalk aquifer holding an estimated 1500 million m3 of water originating from the Chiltern Hills in the north and the North Downs in the south. This was a useful source of water for manufacturing and processing industries in London, with demand peaking in the 1940s when around 150 million litres/day was extracted from over 500 private boreholes. The subsequent migration of industry from central London however has meant the volume of water abstracted has reduced and caused the water table to rise. The General Aquifer Research Development and Investigation Team (GARDIT) undertook a study of the situation and found that water levels in the chalk aquifer are now some 50 m higher than in 1970 and rising at around 2 m a year. Problems posed by the resaturation of the London clay include flooding of deep tunnels such as the tube network, and subsidence as the bearing capacity of the clay is reduced. In 1999 GARDIT, which includes organisations such as London Underground, the Association of British Insurers, Thames Water and the Environment Agency, published a report that recommend de-watering the aquifer by around 50 million litres per day. This will be achieved by a phased programme to drill new boreholes and reactivate existing ones throughout London.Source
Building Sustainable Design