We worked for Southern Gas Networks (SGN) on the gas works site in the Hampshire town of Gosport, situated on a peninsula on the western side of Portsmouth Harbour, opposite the city of Portsmouth.

This project involved the decommissioning (desludging and dewatering) and demolition of Gasholder No.8, the former below-ground 3-lift column guided gasholder, and Gasholder No.9, the former below-ground four-lift spiral gasholder constructed in 1927.

The works included the dismantling of the gasholder and associated plant, along with other additional structures occupying the site and the infilling of all pits to leave an overall clear and level site.

The challenges faced on this site included the proximity of GH8 to the residential property on Dolman Road, and the proximity to Haslar Lake and the noise limit imposed by the local authority during planning to prevent the works from disturbing the local wildlife.

The vessels measured approximately 34 metres in diameter for GH9 and approximately 24 metres in diameter for GH8.

Both of them were constructed of steel which varied in thickness at each of the inner layers, and due to its size and the thickness of the metal, the structure was cut up mechanically using hydraulic shears.

Site overview video:

We were appointed as the CDM Advisor for the project. Our roles included checking the Principal Contractor’s Construction Phase Plan (CPP) and reviewing 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.