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Meridian Water, Wiloughby Lane

The client:Enfield Council
Services:Fabric extraction, of LNAPL and DNAPL, bioremediation, stabilisation, earthworks, groundwater treatment, site investigation, vacuum excavation.

The Challenge:

The 8 hectare former gasworks site at Willoughby Lane had been operational for over 100 years resulting in several distinct sources of contamination, notably; arsenic, cyanide, hydrocarbons, VOC’s and PAH’s in the soils and Dense & Light Non-Aqueous Phase Liquids in the groundwater. The site required remediation to enable it redevelopment as part of a large strategic scheme, Meridian Water, designed to rejuvenate this area of London with the construction of 725 new homes and a new railway station The level of contamination of the soils posed a significant challenge for bioremediation. Conventional groundwater treatment to deal with DNAPL and LNAPL would also require the pumping and treatment of huge volumes of water; alternative techniques were therefore sought to deliver a sustainable of cost effective solution for the site.

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The Approach

Cognition was appointed by Enfield Council to carry out the following remediation works:

  • Installation and operation of a novel technique to target and recover NAPL without the need to pump and treat large volumes of water;
  • The oleophilic fabric extraction system was deployed in recovery wells across the site to clear NAPL to very low levels ;
  • Recovery potential tests using fabric extraction system to determine the mobility and recoverability of the NAPL;
  • NAPL recovery data presented in site clearance/verification reporting.
  • Grossly contaminated soil excavated from hot spots across the site was placed into bunded holding areas for pre-processing to remove concrete, bricks and extraneous waste items;
  • Material was then spread out in 1m deep bunded biopiles and sprayed with additives to bioremediate the soil;
  • Bioremediation treatment was carried out using advanced biodegradation additives selected after site trials to determine optimum mix;
  • Mixing and aeration was provided using tractor mounted soil grinders  and excavators ;
  • Environmental monitoring was undertaken to ensure nuisance odours did not impact local residents;
  • The material was successfully treated to allow re-use on site beneath the clean capping layer thereby negating the need for expensive and unsustainable disposal to a hazardous landfill site;
  • Chemical testing was undertaken for verification reporting of the bioremediation.

The Outcome

Cognition successfully completed the bioremediation works in accordance with the bulk fill criteria and method statement. The bioremediated soil also passed the visual and olfactory assessment. Naphthalene, which was considered to be the most onerous of the contaminants of concern, was reduced from an initial average level of 1,108mg/kg to just 9mg/kg which was well below the criteria limit of 108mg/kg. The NAPL recovery information has been presented in a number of site clearance reports to demonstrate that it no poses a significant environmental risk to the environment. The project has demonstrated that the combination of risk assessment and innovative remediation techniques can bring  seemingly challenging contaminated sites back into use; this project has been recognised within the remediation industry as an example of sustainability and best practice, winning the national Brownfield Briefing Awards Project of the Year 2019.

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