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Water tight

Letters

With reference to the letter from Craig Love (NCE 6 July), there has been a phased increase in groundwater abstraction in the London area in recent years.

The latest report from the Environment Agency on groundwater levels in the chalk-basal sands aquifer of the London Basin shows that it appears to have stabilised and that the risks to tunnels, foundations and basements have been substantially reduced.

This has been achieved by an increase in abstraction of about 70Ml/day and contributes to the 2,100Ml/day available in the south east.

The pressures of 3.5bar on the Dockland Light Railway's tunnel boring machine to which John Franklin refers (Letters 1 June) are consistent with a 35m head of water if the groundwater is in hydraulic continuity with the River Thames. Unfortunately, abstraction and treatment may be expensive due to salinity.

Alan Watson (M), Soil Consultants, alan. w@ soilconsultants. co. uk

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