HS2 Update, December 2021

The first of the huge Tunnel Boring Machines (TBM) will reach Chalfont St Peter in December and break through into the base of the Chalfont St Peter vent shaft shortly after Christmas.  Meanwhile, we remain concerned about the potential damage to the aquifer and our rare chalk streams, particularly considering the TBMs will mine at a shallow depth beneath the River Misbourne at Chalfont St Giles (possibly as early as February next year) then beneath the top end of Shardeloes Lake, near Amersham, later in the year.

Preparation for the main cutting running north from South Heath towards Wendover is now underway with topsoil stripping and further hedgerows and trees being removed.  The main cutting excavation will take place through summer of 2022 with hundreds of thousands of tonnes of spoil being carried along the new construction road  to a ‘temporary’ storage site.

Earlier in the year, along with others, we raised concerns about revised plans for the Leather Lane diversion which would have led to wholesale removal of over 50 mature oak trees beside the existing lane.  We are pleased that the contractors, EKFB, have been able to reconsider their designs and, we are told, a significant number of trees will be saved.  Final numbers of trees lost and saved are yet to be confirmed.

We continue to engage with Natural England, the Independent Design Panel and Buckinghamshire Council to provide advice on developing designs including vent shaft headhouses, overbridges and new road design, noise barriers and landscape mitigation.  We understand that the Schedule 17 planning applications for Bowood Lane, Grim’s Ditch Scheduled Monument and the Small Dean Viaduct will be submitted to Buckinghamshire Council planners in the new year.

A major pollution incident at the Chalfont St. Peter vent shaft came to light following a Freedom of Information Request by members of the Misbourne Protection Group in August 2021. HS2’s contractors, Align, reported the ‘loss’ of 2,400m3 of bentonite clay into the aquifer between August and November 2020 during construction of the vent shaft. This bentonite was reported to have been detected in groundwater 500m from the site.

In May 2021, after attempts over a number of years to secure assurances, the CCB and Buckinghamshire Council set out their shared concerns and a series of questions for HS2 Ltd regarding the impact of the tunnelling on the chalk aquifer. So too did a group of NGOs led by the Chiltern Society, which also developed a briefing on the risks to the chalk aquifer and to the Chilterns chalk stream from its Geological Advisor, Dr Haydon Bailey, a Chartered Geologist who specialises in chalk geology. Despite the confidence of HS2 Ltd and its contractors, they have still failed to satisfactorily answer our questions.

• Designs for the Amersham Vent Shaft Headhouse incorporating anodised aluminium fins have been dubbed locally as the ‘crown of thorns’.
• Originally it was suggested that the site (adjacent to the A413/A404 junction on the edge of old Amersham) required an artistic or architectural statement for the design of this headhouse structure due to the ‘visibility’ of the site being considered to prevent the normal design approach of ‘maximum concealment’.
• A design was developed that employed a semi-transparent circular crown of metallic fins, angled to emulate the slopes of surrounding hills and reflect the sky, creating a dynamic appearance when viewed from a moving vehicle. We expressed concerns about the size of this feature, the materials used and the proposal (at one time) for illumination at night, but the overall idea was favoured by the Independent Design Panel and by Bucks Council officers.
• Over time the designers adjusted their expectations of the necessary size of the structures and associated compound and have made changes to the level of the site to accommodate vehicle access.
• These changes have been so effective as to render the compound and the vent shaft structures themselves almost invisible. Only the artistic aluminium crown was widely visible, and ‘windows’ needed to be left in the surrounding belt of trees in order for the structure to be enjoyed as intended by passing motorists.
• Our planner, Matt Thomson has argued that the rationale for an artistic/architectural statement does not apply if the structure can be rendered almost invisible. The designers have so far failed to respond to requests to provide visualisations of the structures without the ‘crown of thorns’ in place and have continued to defend their design ‘narrative’ even though the design fails to meet the specific criteria in the agreed Detailed Design Principles.
• The schedule 17 application is now being considered, and we have continued to press for practical measures such as increased vegetation screening and removal of the fins which would largely remove the visual impact. We await the outcome of the application with interest.

We will continue working to encourage contractors to meet their own environmental standards, reduce harm and seek what improvements we can to emerging designs.