SearchOval Gasworks
The Challenge:
Oval Village was a residential led development by Berkeley Homes Central London to produce over 1300 homes, a new Tesco Store, over 15,000m2 of community, commercial, office, and retail space and landscaped public realm on the 3.2 hectare site of the former Oval Gasworks, Kennington Gasholder, in the London Borough of Lambeth.
The northern side of the site was formerly occupied by Tesco and Axis Europe and comprised of a supermarket, customer car park and a 2-storey office. The southern side of the site comprised of four decommissioned gasholders, a live gas pressure reducing station (PRS) and various single storey buildings all forming SGN’s depot.
The largest gasholder was grade II listed and was to be refurbished and retained on site. Whilst the northern section of the site was relatively level with adjacent street level, the southern part of the retained site was retained on all boundaries and was approximately 3m higher than the surrounding street level.
Cognition, acting as subcontractor to Woolridge Construction, was engaged in the dewatering and desludging of all the gasholders, the demolition of 3 of the 4 gasholders, and dismantling internal elements of the gasholder to be retained.
The scope included:
- Below ground demolition and above ground frame removal for Gasholders 2,4 & 5
- Removal of internal elements and dome to gasholder 1 with guide frame remaining insitu
- All licences and permits required for the works including MPP2 deployment form for land and ground water remediation
- Environmental monitoring and control especially dust, odour, and Vapour/VOCs as the site is bounded by residential areas.
- Sampling, testing, and verification reporting of gasholder remediation
The Approach
We worked closely with Woolridge during the planning and execution of the works to ensure the stability of the gas holder structures at all stages of the demolition works, including monitoring the stability of perimeter retaining walls, whilst maximising areas available on site for other contractors.
Using our experience in working with regulators such as the Environment Agency, we ensured that all the necessary consents were obtained to enable the works to be carried out without delays.
Gasholder water was treated through The Water Treatment Plant (WTP) provided for this project. The system comprised of an inlet tank, primary particle filtration, buffer tank followed by turbidex filtration and carbon filtration. In addition, a post treatment clean water/mixing tank and a backwash hopper were provided to allow manual backwashing of the turbidex filters. 2 no. bypass loops were provided to allow for the mixing of treated and untreated waters to meet the discharge criteria. Two types of rigorous water sampling were employed: water quality testing and discharge consent testing.
We understood the sensitivity of the site and deployed Environmental Monitoring Points (EMPs) at the site perimeter to ensure all environmental nuisances were kept to a minimum with trigger levels set. Additionally, the control of water generated during installation activities was a key consideration of our works to avoid contaminating water courses.
The Outcome
Cognition successfully cleaned the gasholders, under access and method constraints. The walls and dumpling were jet washed to remove heavy elements of sludge and debris. Each compartment within the annulus was vacuum extracted, whilst the walls and floors were jet washed. Excess materials that remained within the annulus were removed using an excavator.
The Client undertook visual inspection on completion of the works and confirmed acceptance of holder condition.
