Remediation works associated with former Barking Riverside landfill.
Site Background & History
Remediation works at Barking Riverside.
Barking Riverside is one of the largest development sites in London occupying 185 hectares in total and is the largest housing development in the Thames Gateway.
The vision is for Barking Riverside to provide a model for sustainable living in the 21st century. Over the next 20 years it is planned to build 10,800 new homes to house 26,000 people. The development will benefit from new transport links including the East London Transit and the Docklands Light Railway. New primary and secondary schools will also be constructed.
The specific development site described in this case study is the former Renwick Road Landfill. In addition remediation works were carried out on a contamination hot-spot.
The Renwick Road Landfill occupies an approximate area of 2.1km² . The site is bounded to the north by Choats Road which divides the portion of the landfill currently undergoing development from another slightly smaller portion of the landfill to the north. The eastern boundary is formed by a leachate ditch and the south flowing Gores Brook. The southern boundary is delineated by flood defences and the River Thames.
The landfill is understood to have operated as a local authority waste disposal site accepting domestic waste, asbestos waste, inert wastes, gasworks waste and contaminated soils between the 1950’s and 1993.
The landfilled wastes were a highly variable mix of domestic and commercial wastes including soils with strong hydrocarbon odours. An area of shallow suspected gas works wastes in the south-eastern corner of site recorded particularly high cyanide concentrations.
The base of the landfill was identified to be between 10m and 14mbgl – no membrane or engineered clay liner was identified suggesting the wastes lie directly on the natural alluvium.
The contamination ‘hot-spot’ was identified as gasworks waste and specifically spent oxide waste. This material is assumed to have been tipped historically and is currently present within a hollow surrounded.
Site Investigation and Remediation Strategy.
CGL were commissioned to undertake a lead role in the investigation, design, material management for the whole redevelopment. Part of this remit involved a remediation strategy to address identified contamination risks associated with the former landfill.
The revised CGL remediation 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 (these were undertaken by Envirotreat prior to commencement of the remediation works proper, the findings indicated that the proposed treatment minimised cyanide release mobility of the spent oxide waste).
- Source treatment of other identified contamination ‘hot-spots’ (hotspot areas of contamination, both spent oxide and hydrocarbon were previously identified by CGL and remediated by E-Clay stabilisation as part of the overall remediation works undertaken).
- 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 (a comprehensive PRB Barrier design was undertaken and approved prior to the the remediation works being undertaken, the barrier installation works were undertaken over a 10 week programme).
Remediation Works
The barrier system comprised of permeable reactive sections on the eastern and southern boundaries (designed to intercept and treat contaminated groundwater migrating from the site in the direction of the Gores Brook and the River Thames) and a low permeability
section on the south-western boundary of the site designed to channel contaminated groundwater in the direction of the southern reactive barrier section.
The gas works / spent oxide waste identified in the south-eastern corner of the landfill site was delineated and excavated. The
stockpiled spent oxide waste was treated ex-situ utilising the designated stabilisation medium incorporating cementitious materials,
the appropriate E-Clay formulation and specialist additives, to address the concern that highly mobile and toxic free cyanides. Following successful validation (by leachate testing) the treated material was reused as part of the surcharging material requirement in accordance with the material management plan [MMP] for the site Developed by CGL). A further area of spent oxide was treated in-situ.
Three ‘hot-spot’ areas were identified as requiring remediation. It was decided to carry out in-situ remediation due to the significant
depth of the ‘hot-spots’. The ‘hot-spots’ were delineated by the excavation of a number of trial pits. The identified areas were treated in-situ utilising the designated stabilisation medium incorporating cementitious materials and the appropriate E-Clay formulation.
Validation
E-Clay stabilised soils were validated by leachate testing and comparison to the agreed remediation target criteria and PRB Design report.
Groundwater monitoring was undertaken over a five years post remediation. The results collected during this period showed reducing contamination flux over the monitoring period and compliance with the agreed remediation criteria.
