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Wandsworth, London
The Challenge:
The site was occupied by a former gasworks from as early as 1868. The gasworks developed with additional infrastructure including tanks, cranes, retort house and chemical works added over the years to the 1950s until its eventual closure in the 1970s.
Evidence of contamination was recorded at several locations across the site during site investigations. Elevated levels of heavy metals, VOCs, PAHs and TPHs have been recorded within the Made Ground and Kempton Park Gravels, particularly associated with the remnant strictures of the former gasworks. Asbestos fibres have been identified in site soils exceeding the limit of detection. Of particular concern were Light Non-Aqueous Phase Liquids (LNAPL) and Dense Non-Aqueous Phase Liquids (DNAPL) which were recorded in holes located along the northern boundary. These were considered to be a significant risk to the Rivers Thames and Wandle.
The Approach
Following the closure of the gasworks a B&Q superstore was constructed above the residual gasworks structures.
The key elements of these works included;
- Demolition of the former B&Q superstore structure.
- Robust Geotechnical and Geo-Environmental Ground Investigation.
- Break-out of all residual structures including 9m deep gas holders.
- Remove free product with Cognitions Fabric Extraction System (FES).
- Dewatering and treatment of impacted groundwater found within gasholders.
- Bioremediation, both in-situ and ex-situ of 20,000m3 of grossly contaminated soils.
- Cement stabilisation/solidification of engineered backfill.
- Process former structures/hardcore into reusable aggregate.
- Installation of working platforms to facilitate piling.
- Off-site disposal of surplus soils.
- Unexploded Ordinance Probing of pile locations.
- Continual liaison with regulators and residents to ensure a successful outcome to the project.
The Outcome
Cognition developed a cost effective and sustainable Remediation Implementation Plan and successfully remediated the site to ensure it no longer presented an environmental or human health risk. Cognition also carried out enabling works to facilitate the construction phase of 517 residential dwellings within the new development.
