HS2 – C1 – Environmental Monitoring

HS2 C1 – Environmental Monitoring

Sixense have installed 22 Nos. combined Noise and Air Quality monitoring stations that provide ‘real-time’ environmental data whilst being powered by sustainable power sources.Sixense were appointed by ALIGN JV, a joint venture between Bouygues Travaux Public, Volker Fitzpatrick and Sir Robert McAlpine JV, to deliver the noise, vibration and air quality management services on HS2 C1 – a section of Europe’s largest rail infrastructure project over a six-year period.

Supporting nine high-priority construction sites across a complex and high-profile infrastructure corridor including the 16km tunnel underneath the Chiltern Hills and the Colne Valley Viaduct, at 3.4km, the longest railway bridge in the UK.

The scope included the installation, operation, calibration and management of NVAQ, and surface and groundwater monitoring systems. Across the project a maximum of 60 monitors were installed all of which play a key role in the wider efforts to minimise environmental impacts throughout the 6-year build.

We are providing a full maintenance and calibration service on all of the instrumentation as well as undertaking noise and vibration complaint investigation as well as consultancy services.

Within the first six weeks of our involvement, we installed and commissioned 22no. Noise and Air Quality monitoring stations, which are largely powered by sustainable-energy sources.

Sixense consistently averaged above 95% data capture month on month over the project for all monitoring parameters including, but not limited to LAEQ,LMax,L90,L10,PM10,PM2.5,PPV, VDV, Water Level and Flow. Alongside this was technical consultancy and advisory support with monthly reporting over 66 months, 75 attended surveys for specific investigations and 65 Best Practical Means surveys. Technical interpretation of data against standards such as BS5228 and BS8223, Section 61 applications and noise modelling using CADNA were also completed.

Our role was critical in ensuring compliance with environmental commitments, protecting sensitive receptors, and maintaining stakeholder confidence in a highly regulated environment. 

Collaboration & Stakeholder Engagement  

Internally, we worked closely with Align’s environmental managers, planners, and construction teams to support monitoring activities with programme requirements and construction phasing. Externally, we engaged with local authorities, environmental health officers, regulators, and community representatives to ensure transparency and compliance with consent requirements.  

We supported regular stakeholder meetings, contributed to Community Liaison engagement, and provided clear and accessible data on our software platform Beyond. Real-time monitoring platforms enabled stakeholders to access live data, ensuring transparency and building trust across the project lifecycle. This collaborative approach helped resolve issues such as NVAQ complaints using data driven approaches with a personal touch.  

Managing High Priority Sites  

The HS2 C1 section included multiple high-priority sites such as the Colne Valley and the area surrounding South Portal. These were identified by Align and Sixense due to their proximity to residential areas and sensitive natural environments. Furthermore, these would also include the flagship pieces of critical infrastructure such as the Chiltern Tunnel and the Colne Valley Viaduct. Sixense implemented structured procedures to manage these locations, ensuring enhanced monitoring coverage, increased reporting frequency, and rapid response mechanisms particularly during intense site activities including TBM breakout.  

Site-specific risk assessments and monitoring strategies were developed to reflect the sensitivity and complexity of each location. High-priority sites were subject to additional oversight, including frequent inspections, data validation checks, and direct communication channels with key stakeholders including a “daily check” email which highlighted any issues and the status of the resolution. This ensured that risks were effectively and transparently controlled and that any exceedances were identified and addressed without delay. 

Interfacing with EDMS Systems  

Sixense successfully integrated its monitoring and reporting processes with the HS2 (EDMS) – BCDE. All documentation, reports, and quality records were managed in accordance with project requirements ensuring full traceability, version control, and accessibility for stakeholders. Multiple employees were competent in this system allowing cover for absences – a specific client concern.  

Trigger Breach Assessment and Response Procedures  

A key aspect of Sixense’s role was the management of trigger levels for environmental parameters, these were drawn from British Standards and local requirements. We implemented robust trigger breach assessment processes aligned with HS2 requirements, including automated alert systems for NVAQ and water quality thresholds via our Beyond Software.  

During a breach a defined decision chain was activated, ensuring that project teams, environmental managers, and relevant stakeholders were notified promptly via email and SMS. Sixense supported root cause investigations, working collaboratively with construction teams to identify contributing factors and implement corrective actions using our BPM Surveys and methodologies. These were often completed by our consultants analysing the WAV files created during these breaches and using our integrated AI noise recognition software NORA. This gives estimated likelihood for the cause of the noise either construction or non-construction then further analyses the source from a data pool of more than 100 options gathered from 1000’s of recordings.  

Response procedures included immediate mitigation measures, such as adjusting construction methodologies, implementing additional controls, or temporarily halting activities where required. All actions were documented, tracked, and reported, ensuring transparency and compliance.  

Installation, Maintenance, Calibration and Monitoring Systems  

The HS2 C1 sites which required mains powered, solar, wind and battered powered set ups, all which Sixense successfully provided. These varied from isolated rural residential locations to construction boundary areas using mounted poles and securing methods. This included design, installation, commissioning, maintenance, and calibration of monitoring equipment safeguarding data accuracy and reliability. 

Our use of remote and automated monitoring technologies reduced the need for site access while ensuring continuous data collection. System performance was monitored in real time via our daily checks email, with rapid response to any faults or data gaps, maintaining high levels of data integrity throughout the project.