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carbon neutral

Royal Wharf, Silvertown

The client:Oxley Wharf
Services:Demolition, bioremediation, groundwater treatment, permeable reactive barrier, stabilisation.

The Challenge:

Dealing with one of the largest mixed residential and commercial use building developments in the UK, Cognition had to ensure that their remediation strategy was both cost-effective and sustainable. Extensive Site Investigations identified contaminants of asbestos, hydrocarbons, free product contaminated perched ground waters, and made grounds with high levels of heavy metals on the 40-acre site.

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The Approach

Cognition met with the Local Authority and Environment Agency and agreed a remediation strategy for the site that would target the sources of contamination, protect the wider environment and human health whilst providing significant savings to the client. The solution minimised pile mat installation costs using stabilisation techniques, ensured that minimal off-site disposed through re-use of soil under a Materials Management Plan,  and provided protection to sensitive neighbouring receptors (particularly the River Thames) using cut-off walls and permeable reactive barriers. Value engineering ensured that the most cost-effective remediation solutions were used to minimise residual environmental and human health risks. The key elements of these works included;

  • Demolition of buildings and underground structures;
  • Installation of a Permeable Reactive Barrier (PRB) along the northern boundary of the site;
  • Perpendicular cut-off wing walls constructed using a trenching and soil mixing technique;
  • Design and installation of a new river section of wall in response to concerns from the Environment Agency;
  • Removal and treatment of free product using a water treatment plant;
  • Re-circulation of treated water into well points around the contamination hotspots to flush out contaminants or discharged into the local sewage network;
  • Stabilisation of entire site with cement to form piling mats and reduce surface water infiltration during the construction phase;
  • Stabilisation to encapsulate heavy metals;
  • Bioremediation of >320,000m3 of hydrocarbon contaminated soil, reducing TPH from 75,000mg/kg to < 10,000mg/kg and, in most cases, below 1000mg/kg;
  • Preliminary phases of groundworks including construction of spine roads serving the new development.

The Outcome

Cognition’s early engagement with the developers and regulators enabled a sustainable and cost effective remediation strategy to be developed for the site. The works were delivered over five phases and have delivered significant savings to the client in excess of £100M when compared with conventional strategies such as dig-and-dump, extensive water treatment and construction of conventional crushed concrete piling mats.

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