The site formed part of the Tipner Regeneration Project.
The Homes and Communities Agency were developing the site for 80 homes and commercial space.
The site was previously occupied by a range of industries including a tar works, a timber yard and the fuel depot – the soils and groundwater on the site were historically contaminated with a range of organic pollutants including total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, semi-volatile and volatile organic carbons. The site is underlain by a principal chalk aquifer.
The remediation strategy included a requirement for a low permeability barrier (cut-off wall) to isolate the majority of the site from the adjoining land (to prevent both egress of contaminated groundwater prior and during the remediation works and ingress of potentially contaminated groundwater following completion of the works).
The prime requirements were to install a barrier with a hydraulic conductivity of less than 1 X 10-9 m/s and a design life of 75 years.
Envirotreat developed a design strategy for the barrier installation and a mix formulation for the barrier medium (a site-specific formulation of cementitious and bentonitic materials).
Envirotreat then produced a Design Statement for approval by Tamdown and Campbell Reith prior to the installation.
The barrier was installed by a soil mixing process utilising a continuous flight auger. The objective was to install the barrier by the production of overlapping soil mixed columns containing the mix formulation at the designated addition rate.