It’s not unusual for contamination to exist close to sites of special scientific interest and Cognition has vast experience in such projects. This particular project is surrounded by three protected sites, one within 2000 m of the works and two approximately 0.5 Km north east and south west of the site.

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The site is in an area classified as non-aquifer (negligible permeability) status on the Environment Agency Groundwater Vulnerability Map. Ponds and a stream are located 90 m and 200 m to the north of the site. An intrusive ground investigation carried out in October 2009 indicated made ground covers the site, with crushed stone and rubble (0.2–0.7 m thick) overlying scrap yard waste (0.2–1.3m thick).

The scrap yard waste comprised crushed stone, concrete, reinforcing bars, metal, wood, polythene, rubber, plastic and fibre glass. Trial pits also revealed a moderate to strong hydrocarbon odour. Grey silty clay was identified below the made ground with slight hydrocarbon odour in some areas within the top 0.1 m. No significant groundwater strikes were encountered during the site investigation although some perched water was evident.

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Soil samples were analysed for metals and none were found to exceed generic Soil Guideline Values (SGVs). Elevated PAHs and PCBs were found in some soil samples taken from the trial pits excavated on site. Samples were taken from trial pits for speciated TPH analysis although hydrocarbon odours appear to have been more widespread. Cognition carried out further testing to assess PAH and TPHs across the site and obtain more accurate information of the levels of hydrocarbon contamination. The site investigation also revealed some fragments of cement-bonded asbestos across the site although this was not widespread. Nevertheless Cognition included appropriate methods for dealing with Asbestos Containing Materials (ACM).

Remediation works can be summarised as follows:

Additional investigations carried out to supplement earlier intrusive survey in order to provide additional information on soil hydrocarbon contamination and quality of perched groundwater. This also helped to determine if water treatment of ponded water in excavations was required
Excavation of materials
Screening of materials – this included picking of waste items and segregating into various waste streams. Further screening, picking and segregation was required for mid-range materials
Crushing of oversize concrete soils for re-use at 6F2 grade
Ex situ remediation of (hot spot) hydrocarbon contaminated materials in biopiles
Ex situ chemical oxidation of light hydrocarbon contaminated materials in stockpiles
Validation testing of excavation and materials for re-use
Backfilling of treated materials including in situ cement stabilisation of fines.
Compaction and geotechnical technical testing of backfilled materials