This project was undertaken as part of National Grid’s rolling clean-up programme and was the first commercial application of soil washing as a remediation technique in Scotland. Removing the sources of contamination within the 7ha former gasworks site required the excavation of over 8,500m3, including two former underground tar storage tanks.
Excavations were predominantly carried out within ‘running sand’, necessitating careful excavation management along with the installation of sheet piles (in close proximity to live gas mains) to protect off-site infrastructure and services. Upon excavation, soils were assessed and stockpiled for treatment, further analysis or immediate reuse. After classification and screening, 6,500m3 underwent on-site treatment.
Contaminated ‘fines’ were separated from clean sands through a series of different processes within the soil washing plant. The residual materials were then analysed to confirm their suitability for re-use on site. We achieved a reduction of nearly 90% in materials going for off-site disposal. This outcome satisfied the Client’s environmental objectives of minimising both off-site disposal and import of backfill materials.
Groundwater arising from the excavations was also generally contaminated. In order to minimise off-site disposal, a water treatment plant was established. Contaminated groundwater, along with wash water from the soil washing plant, was treated to a level which was acceptable for discharge to the local foul sewer network.
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