High Speed Two (HS2) Ltd. has agreed to fund a £100 million investment in filters and pumps for water treatment plants to address environmental concerns over water quality and water resources in the Chilterns.

Photo: Chiltern Tunnel South Portal aerial view

HS2’s civils contractor on this section of the railway is the Align joint venture consisting of three international and privately-owned infrastructure companies; Bouygues Travaux Publics, a subsidiary of Bouygues Construction, Sir Robert McAlpine, and VolkerFitzpatrick, a subsidiary of VolkerWessels.

Concerns about the impact of HS2 high-speed rail link construction works on water quality, quantity and ground water levels have been expressed by environmental campaigners and local groups.

The Hillingdon Green Party has argued that HS2 poses three main threats to the local water supply system in the Colne valley area which is underlain by a chalk aquifer used by Affinity Water Ltd for groundwater abstraction for public water supply.

With around 3.2 million customers, the company has six groups of abstraction boreholes in the area which take water from the aquifer.

The Green Party says the three main threats are:

• The 13.5 km Chiltern tunnel that emerges near the M25 in the west of the Colne Valley. Twin tunnels are being drilled through the aquifer and risk damaging its structure. The drilling process will also require 6-10 million litres of water to be used daily to transport chalk slurry out of the tunnels, risking increased turbidity or cloudiness in the water, up-stream of the main water abstraction bore holes.
• The 3.4 km Colne Valley Viaduct Over 1,000 acres of valuable waterside, aquatic and terrestrial habitats are being cleared away to make space for temporary access roads, utility diversions, work compounds and spoil dumps. The viaduct will pass only 25 meters away from one of Affinity Water’s main water pumping stations which produces 20 million litres daily. The utility applied for the source to be closed during HS2 construction works due to predictions of increased turbidity. “Hundreds of concrete and metal piles will be driven through the bottom of the lakes and across the entire floodplain, decreasing natural water cleaning processes, increasing impenetrable and polluting surfaces, and changing the structure of the fragile water bearing rock,” the Green Party said.
• The HS2 route is positioned to pass through an underground pollution plume at the eastern side of the Colne Valley, according to the campaigners, pollution coming from the New Years Green landfill site has been responsible for closing the Ickenham water pumping station. Two scheme elements in the area of the underground pollution plume - Copthall Cutting and the deep pile driving for the start of the Colne Valley Viaduct - risk opening up new pathways for the pollution to transit further into the aquifer. “If this pollution reaches the Blackford source then Blackford will need to close permanently and never again provide clean, fresh aquifer water for the public,” the campaigners say.

The viaduct across the Colne valley will be supported by 58 piers, supported in turn by concrete pile caps constructed on groups of piles (numbering between four and nine) made of reinforced concrete with a diameter of about 1.8 metres which will be sunk to a depth of 50 to 80 metres into the ground.

HS2 has recently been ordered to disclose internal documents to Green Party member Sarah Green, a local resident and customer of Affinity Water following her request for environmental information in January 2019. Ms Green had specifically asked:

“What risk assessments have taken place, of the potential increased risk to controlled waters as a result of imminent works by HS2 contractors along the Newyears Green bourne and surrounding wetland?

“Are any of the risk assessments independent from the developers (HS2) and where are the risk assessment (sic) accessible to the public?”

Following a series of unsuccessful attempts by Ms. Green seeking the publication of the unredacted documents via Freedom of Information requests, a final First Tribunal ruling in April ordered HS2 to make three internal risk assessments available to her by 21^st May.

Tribunal : "reports in question concern major infrastructure project which gives rise to substantial and legitimate environmental concerns"

In its ruling, the Tribunal referred to a Petition to Parliament by Affinity Water relating to the High Speed Rail (London-West Midlands) Bill which made provision for the HS2 line in May 2014 which stated:

“ Your Petitioner has significant concerns that the proposed railway passes close to six of its groundwater sources which will give rise to operational issues relating to water quality, quantity and ground water levels. Your Petitioner and its customers could be severely affected as the proposed works have the potential to reduce the quality and/or quantity of water abstracted to the extent that supply could be entirely jeopardised. Due to the nature of the chalk and fissures within it, it cannot be known prior to construction and operation what the effects on the sources will be; as such substantial and careful monitoring will be imperative.....

“Pollution of the groundwater (temporary or permanent) during or following construction may reduce your Petitioner’s ability to abstract from these sources [ie the chalk aquifer]. There is also the risk that pollution will occur as a result of the existence of the railway as the capability of the chalk to filter the water may be reduced by the railway’s positioning. In addition, pollutants from further afield may be able to transit more easily to the sources as a result of piling/tunnelling processes …”

Delivering its decision, the Tribunal said:

“The reports in question in this case concern a major infrastructure project which gives rise to substantial and legitimate environmental concerns. They specifically relate to the risks of contamination to the drinking water supplied to up to 3.2 million people resulting from the construction of the HS2 line. This is clearly environmental information of a fundamental nature of great public interest, as amply demonstrated by Affinity’s Petition and the letter from HS2 to the local MP, Nick Hurd, dated 10 July 2019 which Ms Green produced for the Tribunal.”

The issue has been the subject of widespread media coverage in recent days, including an article in The Guardian newspaper on 31^st May referring to the fears raised over risks of water contamination as result of the HS2 works.

HS2 -  "the internal papers demonstrate HS2 Ltd doing considerable amount of work to account for all potential impacts of construction"

Writing in response in a letter published on 2^nd June, HS2 Ltd’s environment director Peter Miller said he was “disappointed" by the article’s presentation of HS2’s extensive work to ensure good-quality drinking water in north London and Buckinghamshire. He commented:

“The “internal papers” actually demonstrate that HS2 Ltd is doing a considerable amount of work to account for all potential impacts of construction and taking every possible precaution. The project has introduced the latest tunnel-boring technology, and has spent over £100m enhancing water treatment capacity in the region to ensure the highest water quality in these areas. People living near the HS2 route can be reassured that HS2 Ltd is working very closely with the Environment Agency and the local water company to ensure their water is safe and in good supply.”