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Southall, Western Access Road
The Challenge:
Cognition Land and Water was contracted by FM Conway Limited to undertake remediation and earthworks for the redevelopment of the former Southall Gasworks. The site was surrounded by watercourses with a central tip area containing contaminated dredgings from historic watercourse maintenance operations. The main objective was to treat, process and maximise re-use soil materials in the construction of a new access road to development. The scheme included the construction of two new access bridges, a footbridge and associated carriageway and supporting embankments. The soil was contaminated with hydrocarbons, heavy metals, free cyanide, ammonia, PAH’s including benzo(a)pyrene and naphthalene, and benzene. Natural soils were also to be used within the scheme including river terrace gravels, silts and clay.
The Approach
The key elements included;
- Installation of asbestos/dust control measures and carry out background air monitoring;
- Baseline environmental monitoring and installation of dust, odour and asbestos fibre control measures;
- Construction of treatment/biopile areas within tip area and bioremediation and chemical treatment of contaminated soil materials;
- Segregation, hand-picking and disposal of surface deposits of asbestos containing materials (ACM);
- Mechanical screening of contaminated stockpiles to remove extraneous waste (timber, plastics, metal, etc);
- Earthworks to reprofile site for new access road, embankments and landscaping with treated and recovered soils used as engineered fill;
- Stabilisation and compaction of bioremediated soils as engineered fill;
- Construction of flood attenuation pond and realignment/widening of Yeading Brook to improve flood attenuation/capacity;
- Backfilling to road formation in accordance with Series 600 SHW;
- Validation chemical and geotechnical testing of treated soils; and
- Disposal of deleterious/extraneous materials.
The Outcome
A total volume of 30,000m3 of material was processed/ treated and backfilled. Soil material, including contaminated dredgings, was excavated, treated and re-used on site during re-profiling. The remediation and earthworks were carried out in accordance with the remediation strategy delivering a highly sustainable project with significant savings to the client. Stabilisation and dynamic compaction ensured the subgrade material met the geotechnical requirements for construction of the new access road.
