Our projects

Monitoring water pollution during tunnel enlargement

Farnworth Tunnel, near Bolton

A railway tunnel was being enlarged to accommodate two train tracks and an electrification system, which supplies power to railway trains.

To ensure smooth running of the tunnel enlargement, our monitoring team developed a bespoke real-time monitoring system. The 24/7 environmental monitoring system was used to monitor water pollution without the need for manual testing on site.


hour real-time monitoring


second interval monitoring


metre tunnel


Farnworth Tunnel near Bolton was to be enlarged and the waste water needed to be monitored
Our monitoring team came up with a clever solution which would remove the need for manual intervention
Mabey Hire’s environmental monitoring system gives 24/7 highly accurate information

Products used on this project

The challenge

The project consisted of two parallel tunnels nearly 300m in length below the busy A666 at Farnworth near Bolton. The UP tunnel was to be enlarged as part of Network Rail’s electrification project and to accommodate two train tracks. Our monitoring team were working on a solution to monitor water discharge from the boring activities during the project. Network Rail contracted Murphy Group to carry out the project.

Our solution

For the UP tunnel to be enlarged to 9m diameter, it was first filled with 7500 cubic metres of foamed concrete, with structural support installed in the next tunnel to ensure stability during the works. A thrust pit was then constructed and the tunnel boring machine (TBM) was installed. This particular tunnel boring machine was an ‘open face’ variant. This meant that it had two mechanical digging arms which rotate and move on two axes. The process was aided with the addition of ground water when required, any wastewater was then captured in a sump system. This waste then went through a series of filtration processes to ensure that no pollutants reached the local environment.

Traditionally, manual samples are laboratory tested to ensure the suitability of discharge to the local water course. Manual testing is both lengthy and time consuming and does not provide constant monitoring of pollution levels. As an environmentally aware company, Murphy Group worked with Mabey Hire’s monitoring team to develop a more reliable and accurate system to monitor any potential discharge from the TBM.

For this unique project, a Cole Parmer Ph sensor was added with bespoke mountings to allow fitment in the discharge flow area of the final silt filtration tank. Set to take readings at 30 second intervals, this gave a virtual real-time view for the user, 24 hours a day. Data from the sensor was fed into Mabey Hire’s Insite portal where it was available to engineers through a secure web portal.

The Environment Agency was consulted during the development of the systems and was pleased to accept the data presentation methods. Mabey Hire’s environmental monitoring system gives 24/7 highly accurate information without the need for manual intervention, reducing risk of pollution and monitoring cost.

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