Our response to HS2’s news of its intention to start tunnelling in the Chilterns

Chiltern Society Statement in response to HS2 announcement of its intention to commence tunnel boring operations beneath the Chilterns AONB

The Chiltern Society and its partners, the River Chess Association and Buckinghamshire Berkshire and Oxfordshire Wildlife Trust (BBOWT) are today warning that the fragile chalk aquifer beneath the Misbourne Valley – which provides drinking water to thousands of people in the region – is under threat from HS2 Ltd.’s planned tunnelling operations.

HS2 Ltd has announced that tunnelling beneath the Chilterns AONB is imminent, although a licence to commence tunnelling is still to be granted by the Environment Agency.  Despite more than a decade of seeking assurances that tunnelling operations will not damage the fragile chalk aquifer, HS2 Ltd has failed to allay our fears.

When plans to tunnel beneath the Chiltern Hills were first announced in 2010, the Chiltern Society and others raised concerns relating to the potential for significant damage to both the chalk aquifer, which supplies drinking water to many thousands of people regionally and in London, and to the Rivers Misbourne and Chess, which are internationally rare and threatened chalk streams that rely on the aquifer to support this very special habitat and the diverse wildlife that it supports.

The two tunnel boring machines (TBM’s), each more than 10 metres in diameter, will both carve through 16km (10 miles) of chalk from the Chalfont Lane South Portal site, just inside the M25, before emerging at top of the Misbourne valley above Great Missenden.  On the way, these machines will cross the Misbourne Valley twice, passing approximately just 20 metres beneath the River Misbourne at Chalfont St Giles and at the head of the historic Shardeloes Lake.

Our Geological Advisor, Dr Haydon Bailey, confirms that Chalk is an extremely permeable rock in this area and is known to contain intense fracturing and jointing that allow water to pass through the aquifer. There are very significant questions that, even at this late stage, remain unanswered, about how large-scale tunnelling will impact on this fragile groundwater system.

We are therefore seeking answers to the following questions:

  • Will HS2 tunnelling cause irreversible changes to groundwater flow? Will the tunnelling process disrupt water flow patterns, including affecting water supply to –
    • the River Misbourne and other rare chalk streams such as the River Chess?
    • the drinking water abstraction sites along the Misbourne valley and the Colne?
  • Should we expect partial or total loss of flow in the River Misbourne? Between Amersham and Chalfont St. Giles the River Misbourne is “perched” – the river bed is above the water table – and is therefore particularly fragile.  Will shallow tunnelling (at c.20m depth) beneath the river at Chalfont St. Giles cause disturbance to the riverbed and drainage of water from the river leading to permanent damage to this rare chalk stream habitat and loss of wildlife?
  • Will there be pollution to the aquifer? The two TBM’s will grind through the chalk creating a liquid slurry that will be pumped back through the tunnel. Will any turbid water flow be created within the adjacent aquifer and what impact will this have on water supplies and the health of our chalk streams? How will any resulting loss of potable water be mitigated?
  • Should we expect subsidence at Chalfont St Giles? The ground between the bed of the Misbourne and the solid chalk aquifer at Chalfont St Giles comprises unstructured chalk rubble and gravel at least 16m deep. There is potential for the vibration of the TBMs to create subsidence across the path of the twin bore tunnel and for the water to be diverted way from the Misbourne. How will this be mitigated?
  • The reduction of abstraction to protect the Chilterns’ chalk streams has been a long-fought battle. Will recent gains from water companies reducing abstraction be lost with HS2 demanding more water to carry out their tunnelling? Of particular concern, is the huge volume of water required for tunnelling. Precise volumes have still not been fully determined, with latest estimates of the machines requiring up to 10 million litres of water a day. Where will the water come from? Although some water will be recycled, 10 million litres is the equivalent of four days water supply for the whole of the population of Amersham.
  • Once the tunnelling starts, it is unlikely to stop. What contingency plans does HS2 have in place if it becomes apparent that the tunnelling is causing serious damage to the aquifer and to the River Misbourne?
  • Monitoring the impacts of construction relies on data provided by HS2. This is akin to asking students to mark their own homework. What measures will be in place to ensure effective monitoring of the entire tunnelling operation? We are concerned that mitigation plans are inadequate – the mitigation ‘plan’ for the River Misbourne amounts to little more than monitoring for an impact and then exploring how to address the damage, after it has occurred. By this stage irreparable damage will have been caused.

This project, from its very start, has been carried out in totally the wrong order. We would have expected that i) detailed ground surveys would be conducted along alternative routes, ii) detailed discussion would have taken place based on these surveys and finally, iii) a final route would have been selected. Instead i) the route was decided first, ii) public discussion took place based on inadequate data and iii) detailed ground surveys took place identifying all the problematic issues that could have been avoided had the route not already been fixed.

Tom Beeston, Chief Officer of the Chiltern Society, said “We believe that serious questions remain unanswered about the impact of HS2’s tunnelling operations on our precious chalk streams and the availability of drinking water for local communities.

“We are particularly concerned that the HS2 Act has weakened the Environment Agency’s powers to monitor and regulate the impacts of tunnelling upon the aquifer and our chalk streams. We want assurances that the Environment Agency remains able to protect our environment and public health.”

Unfortunately, we are now in the position of hoping for the best but fearing the worst. Only time will tell if our aquifer will remain intact and our chalk streams survive.

The only solution that would ensure that minimal damage is inflicted on the aquifer would be to tunnel through the clay under the aquifer


Notes to editors

The Chiltern Society was established in 1965, we have 7000 members, manage 12 conservation sites, and have 500 volunteers who work tirelessly to maintain and improve the Chilterns for the benefit of both residents and visitors alike.

Every year our volunteers contributed around 250,000 hours, to manage and improved several nature reserves and heritage sites, created long distance footpaths and cycleways (including the Chiltern Way), reviewed hundreds of planning applications and maintained thousands of miles of footpaths and bridleways.

We have campaigned for many years against the damaging effects of HS2; increased our activity and voice concerning many serious threats to the Green Belt across the Chilterns; promoted the heritage of the Chilterns through our annual Heritage Festivals; and offered an extensive programme of walks, cycle rides and events throughout the year.

Interviews are available with:
Haydon Bailey PhD CGeol FGS – Geological Advisor
Cllr. John Gladwin – Lead Trustee on all matters related to HS

Further information

For further information and interviews please contact Tom Beeston, Chief Officer at the Chiltern Society on 01494 936 473 or at TomBeeston@ChilternSociety.org.uk

Chiltern Society Letter to Sir James Bevan 28 April 2021 (1)

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HS2 apply for Licence to bore the Chiltern Tunnel through the Aquifer

This was established when at the Society’s request, Lord Berkeley asked written questions with regard to this – see link.

The answer is concerning. Of the three assessments submitted, two are in draft.

We have raised the issue of the risks of tunnelling through the aquifer since this route through the Chilterns was decided upon nearly 10 years ago. The key issues relate to:

  • The risk of losing the River Misbourne through water diversion
  • The risk of polluting the drinking water for local people and London

It is almost unbelievable that having ordered the tunnel boring machines and being ready to start tunnelling, HS2 Ltd had not applied to the Environment Agency for a licence. The EA has less than two months to agree or deny the licence. Not an enviable task, when two of the key assessments are in draft only.

The Ground Investigation work carried out by HS2 has demonstrated the fractured nature for the chalk in the Misbourne aquifer. This has been confirmed by an updated geological survey by the British Geological Survey.

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Changes in Water Abstraction licences

Affinity Water has made an application to increase its water abstraction at Watford. This is to ensure that water supply can be maintained if HS2 adversely impacts the water supply in the Misbourne Valley. However by increasing the water abstraction at Watford, this could impact the flow of water in the River Gade.

Have your say at:


But be quick, the final date for responding is 26th Feb 2021.

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“Area of Neighbourly Behaviour” report – HS2

Last Friday the Chiltern Society issued a report on the experience of HS2 construction in the AONB, in the eight months following Notice to Proceed. This contains numerous examples of environmental destruction,  the lack of community engagement, and persistent  un-neighbourly behaviour, which we have come to associate with this project .

The Government also  responded to the recent petition Stop work on HS2 immediately and hold a new vote to repeal the legislation , promising “a clear commitment to greater transparency”, and “a range of measures to mitigate and compensate for environmental impacts”. Our report illustrates a few of the environmental impacts, and the scale of mitigation which would be required to compensate for them. We note that there are no new promises regarding engagement and neighbourliness in the response, or acknowledgement of the failures to date in this area.

We hope that the report will have some influence when the petition is debated in Parliament.

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Leader of the Council calls out HS2 Limited’s attempts to keep local residents informed

proposals to Parliament.  Faced with the delivery phase of this unwanted project, the least we should expect is considerate, well communicated implementation.  However, despite the assurances from HS2 that they will be a “good neighbour” we are not currently experiencing that.  Instead HS2 issues are diverting tax-payers’ resources away from delivering vital services during a pandemic, as we are having to deal with countless local issues which are caused, and not adequately addressed, by HS2 Ltd and its contractors.

The Council has historically opposed the HS2 project and continues to do so for many valid reasons.  It dissects the county and provides no tangible benefits to Buckinghamshire.  We have all the dis-benefits of a large-scale construction project and none of the benefits, with the damage being done to our environment and the visual impact completely irreversible.”

At the meeting of the TSC on 6 January, it’s second six monthly oral evidence session on the progress of HS2, evidence was given by Phil Gaskin, Chairman of Calvert Green Parish Council, an area hugely impacted by HS2. He stated “that there is no quick and simple way of resolving issues with HS2 Ltd.”

Both Greg Smith MP for Buckingham and Mr Gaskin raised the need for independent oversight of the project and suggested the implementation of local sheriff style appointments, to be told by Mark Thurston, HS2’s CEO that these roles were already in existence. No-one has seen these officers in Buckinghamshire.

Councillor Tett added: “On this basis I urge the Select Committee to ensure that there is effective monitoring of the contractors and HS2 Ltd’s decisions to implement the project differently to the proposals set out to Parliament, and for Buckinghamshire Council to be appropriately re-imbursed for the additional pressures which the project implementation is putting on the authority.”

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Petition to hold a Public Vote on HS2

A Petition has been set up calling for the Government to told a Public Vote as to whether to continue with HS2.

See link here.

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Amersham Vent Shaft Consultation

HS2 have launched a consultation seeking views on their proposed design for the Amersham Vent Shaft, to be constructed beside the A404 at the junction with Whielden Lane. At some point it has been transformed from a boring Green box into a ‘Key Design Element’, and will be a landmark feature on the road into Amersham, if HS2 have their way. Is that what we want? See this page for  links to the design  and some comments on the consultation questions.

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Is the HS2 twin-bore Chiltern Tunnel Design Safe?

The Society has written to Andrew Stephenson MP, Minister for HS2 asking for confirmation that the Chiltern Tunnel design will meet the Operational Safety Requirements.

We have engaged with HS2 Ltd over the past 10 years to establish whether the current Chiltern Tunnel Design is safe. We have asked a number of questions regarding evacuation procedures for which we have not received answers. Recently we were informed that they were not in a position to answer our questions.

If the design is not operationally safe, HS2 will not be able to run 18 trains per hour each way at 320kph. This would severely impact the Benefit/Cost Ratio, which is already poor.

The key issue is, if a train has to stop in a tunnel, the 1,100 people on board would need to be moved to a ‘Place of Safety’ prior to be being transferred to a Final Safe Place. Currently this requires the passengers to move to the ‘other tunnel’ via cross passages to stand on a platform 1.6m wide for up to two hours while waiting for already full trains to arrive to remove them.

HS2 – Letter to A Stephenson Jul 20

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HS2 archaeologists uncover Iron Age murder mystery and Stonehenge-style monument at Wellwick Farm

Archaeologists working on the HS2 project in Buckinghamshire have made an eerie discovery, unearthing a skeleton believed to be a murder victim from the Iron Age. Other discoveries at the Wellwick Farm site near Wendover span over 4,000 years of human history, and include a circular timber monument resembling Stonehenge.

See link to the full article.

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