The Bromley site occupies an area of approximately 7 acres. The site is contaminated with pollutants from historical activities near the site, most notably from the adjacent gasworks. It was the intention of ProLogis (Developer) to redevelop the site for commercial / industrial end use.
The contaminants of concern originated from the nearby gasworks and surrounding industrial area and include, Cyanide, Ammonia, PAH’s and TPH. They are located predominantly within the made ground and underlying gravely clay.
The remediation strategy at the Bromley site was to install an Active Containment System comprising an active (permeable reactive) barrier incorporating Envirotreat modified pillared E-clays® . This remediation approach addressed the on-site contamination problems and prevented the potential risk of future contamination of the adjacent site through groundwater migration.
The Envirotreat Soil Mixed Re-active barrier contains modified pillared E-clays designed to remove and chemically immobilise the prime pollutants of concern, which are primarily organic in nature. The clays incorporate the requisite treatment capability for the effective treatment of both cationic and anionic metallic species onsite.
The works were conducted over a 2-week period under the auspices of Envirotreat’s Mobile Process Licence (MPL). Specialist technology, materials and supervision were supplied by Envirotreat, whilst Norwest Holst supplied all the required plant, and labour for application of the Envirotreat® Process.
The total length of the active barrier was 80 m, with an average depth of 9m (the total depth varied with the depth of the underlying clay into which the barrier was keyed into).
The barrier was installed by advanced soil mixing techniques using continuous flight auger systems. The active barrier comprised a single row of overlapping columns (each column having a nominal diameter of 900 mm).
Envirotreat were requested to undertake the validation of the barrier. Two boreholes used in the initial site investigation were utilised for validation. They are situated outside of the contaminant plume and in line with the anticipated migration path.