The Harmondsworth site (plate 2) occupies an area of approximately 7.5 acres. Extensive contamination was identified with soil and groundwater polluted with chlorinated hydrocarbon.
It was the intention of Kingswood Commercial Developments to redevelop the site for commercial / industrial end use.
The remediation strategy at the Harmondsworth site was designed to address the on-site contamination problems and prevented the potential risk of future contamination of the adjacent site through groundwater migration.
Envirotreat installed an Active Containment System comprising both non-permeable and permeable sections (figure 1). The Envirotreat Technology at the Harmondsworth was applied using a Continuous Flight Auger (CFA). The active (permeable) section of the barrier contained modified pillared E-clays® designed to remove and chemically immobilise the prime pollutants of concern. The non-permeable (passive) sections of the barrier are composed of a clay and cement mix. Passive barrier sections are used to channel groundwater towards active barrier sections where contamination can be ‘filtered’ out. Nonpermeable barrier sections are included to reduce installation costs as their raw materials are cheaper than those of the active sections.
The works were conducted over a 12-week period under the auspices of Envirotreat’s Mobile Process Licence (MPL). Specialist technology, materials and supervision were supplied by Envirotreat, whilst May Gurney supplied all the required plant and labour for application of the Envirotreat® Process.
The total length of the active barrier was 800m, with an average depth of 7m (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)