Basford Gas Works, Soil Washing

As part of National Grid's ongoing programme to reclaim former gas works, VHE were contracted to undertake the reclamation of Basford Gas Works in Nottingham.

Basford was unique in that it was chosen by National Grid to trial the first large scale soil washing project in the U.K., using the process as a waste minimisation technique instead of the traditional "dig-and-dump" method of reclamation.

Approximately 120,000 tonnes of predominantly granular fills and contaminated sands and gravel were treated by soil washing to produce clean fill material for re-use on site. Other works undertaken included selective digging, ash recovery, tarmac recycling, crushing, screening, off site disposal of special wastes and the import of suitable clean material. Ground investigation works and final site validation testing were also undertaken concurrently with the main contract works. These investigations confirmed the effectiveness of the soil washing process and verified that the specified engineering characteristics of the site were achieved.

Realising the important research and development aspects of this project, and the difficulties of managing the logistics of integrating the new technology within the main reclamation programme, VHE redefined the role of principal contractor, and worked in partnership with the specialist sub-contractor, the consulting engineer and the client in order to ensure the success of the project, both in technical and commercial terms.

More than 150,000 cubic metres of material was excavated from the seven hectare site, to depths in excess of eight metres. Much of the excavation was undertaken below the groundwater table and below geological rock-head. This required the continual pumping and management of considerable quantities of contaminated groundwater to an on-site water treatment plant for decontamination. This groundwater was then disposed of via the main sewer or re-used in the soil washing operation.