Site Background & History
The site was formerly a petrol filling station situated in Chingford, London. The client [Anderson Group / Constable Homes] had previously obtained planning permission to develop the site for the construction of eight residential units.
The site is relatively small occupying an overall area of 0.12 hectares. Previous site investigations undertaken by Card Geotechnics Limited [CGL] identified the presence of significant hydrocarbon contamination in both soil and groundwater consistent with the previous usage of the site as a petrol station. The prime contaminants of concern were Total Petroleum Hydrocarbons [TPH], BTEX and Naphthalene. CGL carried out a risk assessment which identified significant risk to both human health and controlled water receptors.
CGL also identified the presence of five underground fuel storage tanks.
CGL considered a number of remediation options including pump and treat, chemical treatment, monitored natural attenuation (MNA) and the installation of an activated clay barrier. After due deliberation it was decided to progress the remediation of the site utilising a combination of source and groundwater [pathway] treatment as an integrated treatment approach – the preferred remediation strategy was a combination of E-Clay Stabilisation for the source treatment requirement and the installation of an E-Clay ‘Activated’ Permeable Reactive Barrier to treat potentially contaminated groundwater migrating from the site.
The remediation strategy was considered to be commercially viable and provided a remediation solution which addressed the identified remediation requirements in an acceptable timeframe for the development. The other remediation options were precluded on the basis of cost and / or inability to achieve site remediation within the required timeframes. The necessary approvals for the proposed remediation strategy were obtained from Waltham Forest Borough Council and the Environment Agency.