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St Levans Road Gas Holder, Plymouth

Working for our client and site owner, Wales and West Utilities plc, the Dorton Group were contracted to supply and fill with clean inert soil for the backfill of the former gas holder tank at St Levans Road, Plymouth.

Following the removal of the holder and frame by others, the site had lain idle for some time during which the tank void had filled with rain and ground water totalling around 10,000m³ (figure 1). This residue had to be pumped off at a controlled rate over a period of 3 weeks so as not to overload and exceed the capacity of the local drainage channels.

The tank area to be filled was estimated to be 15,000m³ in the solid. The specification for the fill was to supply clean inert soil only, devoid of stone, brick or concrete other than small fragmented pieces. A quality assured chemical testing regime was required that checked PH levels and the presence of any hazardous or contaminated substances every 500m³ supplied. The project was carried out under the auspices of CL:AIRE, Contaminated Land: Applications In Real Environments to ensure that all criteria for the remediation of the area was strictly adhered to.

Because the site was located close to residential and commercial properties and at peak times there were around 100 lorry movements per day, a representative of all these occupiers was appointed to liaise with Dorton Group to provide real time solutions to any concerns. A number of control measures were put into place and remedial measure were enacted over the contract period to ensure that all residents and occupiers were satisfied. Some of these measures included fortnightly cleaning of cars and windows, daily cleaning of roads and the cleaning of house facades at end of project.

All fill material was sourced locally diverting around 18,000m³ from landfill, to be placed and consolidated in 250mm layers with a ‘sheeps foot’ roller (figure 2). The granite tops of the tank were lifted off and reclaimed for re-use. The concrete broken from the tank walls was taken to the Dorton Group recycling facility at Challonsliegh and crushed and screened for recycling with some of this material returned to site for capping (figure 3). The project period ran through from February 2013 to August 2013 with a total value of £250,000

Figure 1

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Figure 2

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Figure 3

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Dorton removed the asbestos, demolished the structure and carried out the initial excavation for the new building, all within a 14-weeks programme, as planned.

St Paul's School