The Barking Riverside development will create a new neighbourhood alongside 2km of Thames river frontage. 180 hectares in area, it is one of the most ambitious and important new brownfield developments in Europe, and will include 10,800 homes, healthcare facilities, schools, open space, a new rail station and commercial space.

In the 1900s the site housed the UK’s largest power station, with associated pulverised fuel ash lagoons. Part of the site was also used as a landfill up to the 1980s.

Remediation of the landfill area was required to mitigate potential risks to the adjacent controlled waters. In addition, the landfill material required reprofiling to accommodate a capping layer and to achieve the proposed Masterplan levels, allowing future redevelopment.

Enhanced Remediation Strategy
The initial remediation strategy for the landfill site submitted with the outline planning application included an extensive programme of ground improvement with a fully engineered capping layer, a gas dispersion blanket and low permeability capping to prevent infiltration and leachate creation.

CGL undertook a targeted phase of investigation, landfill characterisation and detailed quantitative risk assessment to derive a revised remediation and ground improvement scheme that was much more pragmatic and cost effective. CGL’s scheme significantly reduced the extent of works required, realising cost and programme benefits.

Enhanced Remediation Strategy

The revised strategy was fully approved by the Environment Agency and local authority. It comprised:

• Treatability trials of materials impacted by spent oxide which were rolled out into a remediation process using soil stabilisation and encapsulation techniques.
• Source treatment of other identified contamination ‘hot-spots’.
• Design and implementation of an E-Clay Permeable Reactive Barrier (PRB) to mitigate potential risks to the neighbouring Gores Brook and the River Thames from perched groundwater and landfill leachate. The barrier was installed down to the underlying cohesive alluvium at a depth varying between 3.5m to 7m below ground level.
• Reprofiling of site levels under a Materials Management Plan as part of the overall earthworks strategy to achieve a site level 1.5m below the Masterplan levels. All material reuse was undertaken under the CL:AIRE Definition of Waste: Development Industry Code of Practice.
• Placement of a capping layer across the landfill area using chemically and geotechnically acceptable site-won material from surcharge removal works.

Remediation Supervision and Verification

CGL oversaw the remediation work and the treatment was verified by CGL with the contractor to check the water flow through the E-clay barrier met the approved contaminant concentrations at the receptor. The barrier was shown to reduce the contaminant concentrations by up to 95%.

Post Remediation Settlement Analysis

Following the remediation and reprofiling works CGL carried out additional investigations on the landfill area to confirm the current ground model. This has measured the thickness of the capping layer and used forensic total organic carbon testing to predict the extent of future degradation of waste material.

CGL then used numerical modelling techniques to predict future settlement such that proposed buildings and infrastructure can be designed and constructed with minimal further ground improvement works.