In 2020, Cognition teamed up with Climate Care to offset our total annual emissions and becoming Carbon Neutral for the first time. In the same year, the company committed to stay proactive, adopting and developing more sustainable remediation methodologies, selection of materials and energy sources we use, reducing the need for offset element of our emissions. Our long-term goal is to continue improving efficiency and minimise emissions from our routine site and office operations across the board.
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Steetley Chemicals, Worksop

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The client:Laing O'Rourke
Services:Bioremediation, groundwater treatment, mechanical segregation of extraneous waste/asbestos, stabilisation/encapsulation, chemical oxidation.
Duration:2 years 1 month

The Challenge:

The 85 hectare site was previously occupied by a refractory brick works, quarry, colliery, various small industries and a 25,000m3 waste tip. This was remediated so that the site would be suitable for future redevelopment. The principle contamination on the site was hydrocarbons with TPH concentrations up to 30,000mg/kg and volatile and semi-volatile organic compounds. Heavy metals, including barium, lead and copper, were also found in pockets. Contamination hotspot areas on the site included above ground storage tanks, a pitch impregnation plant area, chemical storage facilities and localised areas tipped with miscellaneous wastes and asbestos materials. The contamination found in the former sub-station has resulted from oil leaking through the former basement construction directly into the limestone aquifer and impacted groundwater quality.

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The Approach

Cognition was contracted by Laing O’Rourke to remediate the Steetley site, maximising re-use and minimising disposal costs. The site was to be redeveloped for commercial and industrial use following remediation. Remediation was widespread across the site and involved removing and treating the landfill, treating TPH hots spots across the site, bioremediating made ground and carrying out in-situ treatment of groundwater contamination sources. The key elements of these works included;

  • Bioremediation of 60,000m3 of TPH and PAH contaminated soils;
  • Laboratory trials to test additives and cultivate indigenous bacteria for use on site;
  • Clay cut-off walls were installed across the site to protect completed remediation phases from cross-contamination;
  • Soil materials with concentration >2% TPH were used in the foamed asphalt plant to produce tarmac for new site roads;
  • Screening of 25,000m3 of mixed waste and soil to remove oversize material, extraneous waste items and visible asbestos;
  • Stockpiling and testing of soil to ensure it met re-use criteria or required bioremediation;
  • Treated soil was stabilised and reused to backfill the excavations;
  • Groundwater was treated ex-situ and recirculated to flush out contamination.

The Outcome

TPH contaminated soil was successfully remediated and re-used on site as backfill. Approximately 2000m3 of soil with TPH concentration >20,000mg/kg was re-used in the foamed asphalt plant to form tarmac for site roads. The landfill area was excavated treated and backfilled with treated stabilised soil to produce a suitable construction platform for the new development. The site has since been successfully redeveloped by the client.

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