HS2 tunnel could damage water supply
Current plans for the HS2's Chiltern tunnel could damage water supply in Buckinghamshire if given the go ahead, the High-Speed Rail Commons Select Committee has heard. Giving evidence to the committee, geologist Dr Haydon Bailey told the committee that a major regional water supply could be damaged by drilling just one hole.
Dr Bailey said HS2's plans to bore through the Misbourne Valley are worrying because the tunnel crown will be at a level with less than 6m "of competent chalk above it. Above this will be gravel and weathered rubbly chalk and there is certainly the threat of ground failure at the valley crossing point close to Chalfont St Giles".
He proposed that a three-layer tunnel would be better, protecting the water supply and allowing emergency access.
"The proposed route crosses the Misbourne Valley where the tunnel crown will be at a level with less than six metres of competent chalk above it. Above this will be gravel and weathered rubbly chalk and there is certainly the threat of ground failure at the valley crossing point close to Chalfont St Giles," said Dr Bailey.
He said: "The chalk aquifer below the Misbourne valley is a major regional water supply, with numerous public water sources/boreholes in proximity to the proposed route. The public water supply at Chalfont St. Giles will certainly be jeopardised by the tunnel construction, and several other boreholes along the Misbourne valley at Amersham and Great Missenden will be threatened.
"In addition to this, 22% of London's water supply is at risk should there be any damage to or pollution of the chalk aquifer in this and the adjacent Colne valleys."
The HS2 is the proposed high speed link between London and the Midlands.
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