Active containment system for a former industrial site in East London

Abstract

The site in question lies in a highly industrial area of East London where widespread and varied contamination is present in many areas as a result of historical and current activities. This is further compounded by the high sensitivity of the underlying groundwater (inner groundwater protection zone) and the proximity of the River Lea, which lies along the eastern boundary of the site. The site encompasses an area of approximately 0.3 ha. Site investigation undertaken between June and August 2002 confirmed the presence of 3 to 4 m of highly contaminated Made Ground, with groundwater present in the underlying River Terrace Deposits at 2.5 to 3 m below ground level. Soil chemical analyses indicate highly elevated soil concentrations of heavy metals and organics. Groundwater contaminants comprise both inorganics and organics. Based on the findings of the ground investigations, it was considered that the most economically and environmentally sustainable remediation solution for the site was the use of an Active Containment System (ACS) in the form of a cut-off wall extending into the deep impermeable clays of the Lambeth Group. Active sections, placed at upstream and downstream locations, comprise activated clay to immobilise and absorb both organic and inorganic pollutants in groundwater whilst maintaining a permeability similar to the site geology to limit impacts on the local hydrogeological regime. A Remediation Method Statement for the site was submitted to the Environment Agency in October 2003. This article outlines the background to the site and the reasoning behind the use of an ACS. In addition, it describes the details, constraints and general procedures required for the installation and design of such a system.