Remediation works associated with former Barking Riverside landfill.
Site Background & History
Envirotreat was commissioned by Bellway Homes to undertake remediation works at Barking Riverside. The site was the former landfill adjoining the River Thames
The Barking Riverside development 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 and the creation of the new Barking Riverside station. New primary and secondary schools will also be constructed.
The development site described in this case study is the former Renwick Road Landfill and further remediation of the wider development area.
The Renwick Road Landfill occupied an approximate area of 2.1km2. The former landfill site is bounded to the north by Choats Road which divides the portion of the landfill in two part the southern larger part currently undergoing development and the norther 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. To the west is further scrub land part of the overall development area.
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.
Historic site investigations indicated:-
“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.”
Site Investigation and Remediation Strategy.
CGL was 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:
- The Regulators necessitated the requirement to undertake comprehensive treatability trials of the spent oxide materials. The proposed remediation strategy was soil stabilisation and encapsulation. Envirotreat undertook site sampling and treatability trials prior to commencement of the remediation works. The findings indicated that the proposed treatment strategy minimised / reduced free cyanide release / mobility from the spent oxide waste.
Figure 1 – Spent oxide waste onsite.
- Stabilisation and encapsulation of other contamination ‘hot-spots’ (predominately tarry waste with highly elevated TPH and PAH).
- Design and installation of an E-Clay Permeable Reactive Barrier (PRB) along the southern and eastern extent of the landfill site to mitigate potential risks to the neighbouring River Thames and Gores Brook respectively from perched groundwater and landfill leachate. A further short section of low permeability barrier was required along the western landfill boundary. The barrier was to be installed down into the underlying cohesive alluvium at a depth varying between 3.5m to 7m below ground level. A comprehensive PRB design was undertaken and approved prior to 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.
Figure 2 Northen section of Gores Brook PRB.
Figure 3 Section of River Thames PRB.
During the remediation phase of the works, gas works / spent oxide waste previously identified in the south-eastern corner of the landfill site was fully delineated and excavated. The spent oxide impacted soils were stockpile next the treatment area. The spent oxide contaminated soils were treated in batches utilising the designated stabilisation medium incorporating cementitious materials. This E-Clay formulation was based on the findings of the treatability trials specifically to address the concern of highly mobile and toxic free cyanides. Following treatment representative samples were taken and submitted to an MCERT accredited laboratory for leachate testing. Leachate data was compared to the agreed remediation target criteria, successfully validated materials were reused as part of the surcharging material requirement in accordance with the material management plan [MMP] for the site (as developed by CGL). A further area of identified spent oxide (outside of the landfill site) was treated with the same E-Clay formulation and treated in-situ (by adding the E-Clay slurry direct to the contamination area).
Figure 4 Excavation of spent oxide waste along the eastern landfill boundary with the Gores Brook.
Figure 5 Ex-situ treatment of spent oxide waste.
A number of ‘hot-spot’ areas were identified as requiring remediation. Based on site constraints (depth of contamination and ground instability), it was determined that the most appropriate methodology was to carry out in-situ remediation.
The ‘hot-spots’ were delineated by the excavation of a number of trial pits around and through the contamination ‘hotspots’. The identified areas were treated in-situ utilising the designated stabilisation medium incorporating cementitious materials and the appropriate E-Clay formulation.
Figure 6 In-situ treatment of spent oxide waste in the north east of the development (outside the landfill area).
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 by installing a series of groundwater monitoring boreholes down gradient of the PRB installation along the length of the PRB. Groundwater quality was monitored over five years. The data was shown to be acceptable and approved by the regulators.
