Project: Southend-on-Sea Former Gasworks
Client: Major House Builder
Contract Value: £1,800,000

Knight Environmental Limited remediated part of the 5 hectare former Southend-on-Sea Gasworks site located on the Eastern Esplanade which had been previously been considered uneconomical to develop due to its legacy of historical contamination. The site had stood derelict for over 10 years and now over 200 residential units and associated amenities including a health centre and hotel are being developed.

Site investigations identified typical gasworks residues such as elevated hydrocarbons and metals within the soils on site. The site comprised of the original hardstanding and below ground foundations as well as the infrastructure of the gasworks including below ground tanks and associated pipe work.

The enabling and clearance works commenced in the spring of 2003 with completion of soil remediation works in August 2004. The soil remediation works generally comprised the construction of a 1.5 metre thick capping layer following removal of the existing below ground tanks and associated pipework. A 1.5 metre strip was excavated, stabilised and re-used on-site achieving a re-use target of 75% of materials. The minimisation of off-site disposal resulted in significant cost benefits to the client with a significant decrease in the potential disruption and nuisance to the local traffic. This was in line with Knight Environmental Limited’s policy of pragmatic and sustainable solutions.

Over 15,000 cubic metres of contaminated soil were excavated, sorted and treated with the patented e-Clays, using specialised Knight Environmental Limited plant. This chemically stabilised the soil which significantly reduced its leachability and allowed for its re-use on site. The excavated areas were backfilled with treated soils above a geotextile membrane placed at the dig level. A crushed concrete capillary break layer was placed at the finished remediation level. A capping layer comprising of topsoil overlying subsoil was placed in the gardens of the finished development.

The need for costly groundwater treatment was removed due to the stabilisation of the worst contamination which enabled the Environment Agency to approve a strategy of monitored natural attenuation.

The remediation work was scheduled in accordance with our Client’s development needs and allowed for a phased approach to validation and approval by the Regulatory Authorities.