According to geologist, Dr. Haydon Bailey, HS2’s current plans to construct the Chiltern tunnel could have an adverse effect on the regional water supply. Drilling one hole into the chalky ground could weaken the ground entirely, potentially risking ground failure.
The controversial HS2 rail scheme is the proposed high-speed rail link between London and the north of England, with the first phase linking London and Birmingham expected to be open in 2026. Whilst the project is expected to bridge the north-south divide and boost the economy, there is disagreement over the burden of cost on the taxpayer, the disruption to local communities and the environment.
Dr Bailey emphasised that if the tunnel goes ahead, its crown will have just “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.”
"The chances of the River Misbourne surviving this must be close to zero with the resulting loss of environmental benefits, wildlife habitats and public amenities.
"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 per cent 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.”
Representing Westminster’s High Speed Rail Committee, John Gladwin said a three bore tunnel was the only viable tunnel option which would considerably reduce the risk to the aquifier and eliminate damage as it’d be built deeper in more solid chalk.
A middle tunnel would also afford passengers extra safety in the case of an emergency or incident whereby a train has to be evacuated.
"We believe our case for a three bore tunnel is a matter of balancing the extra construction costs against the value of conserving the AONB and the environmental and other benefits, including increased passenger safety.
"Whilst this cost is quite considerable it represents only a tiny percentage of the overall construction cost while enabling the government to meet its commitments to conserve and enhance the AONB".