We worked for Southern Gas Networks (SGN) on the gas works site in the Buckinghamshire town of Aylesbury.

The project involved the decommissioning (desludging and dewatering) and demolition of the former above-ground spiral-guided gasholder. The works included the dismantling of the gasholder and other additional structures currently occupying the site and the infilling of all pits to leave an overall clean and level site.

Gas holder decommissioning is normally considered difficult due to the significant health hazards and the associated environmental impacts. In this particular project, the process was further complicated as the site was located within an industrial estate with the only access being via a builder's merchant with the ancillary structures located in a separate area within the merchants, which in turn meant that traffic management was given higher priority than usual.

The tank was constructed of steel and measured approximately 35 metres in diameter, and due to the thickness of the metal, the structure was cut up mechanically using hydraulic shears with no section of the works being ‘hot cut’.

Site overview video:

We were appointed as the CDM Advisor for the project. First, we began by reviewing the Principal Contractor’s Construction Phase Plan (CPP) and the Risk Assessment and Method Statement (RAMS) for the project before issuing the authorisation to commence construction activities.

Throughout the project’s period, we carried out audits which were planned to coincide with the specific phases of the project. Such audits included the CDM compliance audit, a specific environmental audit to ensure the sludge and waste were removed in line with the Environmental Agency’s requirements, and a process-specific demolition audit.

• Review and comment on the Construction Phase Plan and issue a report.
• Review and comment on the Risk Assessments and Method Statement and issue a report.
• Carry out the pre-start CDM site audit and issue a report.
• Carry out the environmental site audit and issue a report.
• Carry out the demolition process site audit and issue a report.