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The Former Croda Works Design and Build

The site was an 11ha former tar chemicals works with gross soil and groundwater contamination. Sirius developed and implemented an innovative, cost-effective remediation strategy, while working closely with the client and regulators to obtain approvals for residential development. The remediation techniques included both a sophisticated capping system and Sirius proprietary solidification-stabilisation using the forerunner to our STAR system.

Client Name: Gleeson Homes and Regeneration



Project Description

This 11.5 hectare site had been operated for over 100 years as a tar chemical works and there was extensive gross contamination of soil and groundwater as a result of historical spillages and waste disposal practices. As part of the Design & Build package undertaken by Sirius, an intensive programme of works was undertaken to develop and validate a robust and cost-effective remediation strategy to enable residential redevelopment.

Close working liaison with the contaminated land team at Rotherham Metropolitan Borough Council and the Environment Agency throughout the process enabled approval of the remediation strategy to take place rapidly, thereby achieving the earliest possible regeneration of the land.

Activities and Innovation

Site Investigation
Sirius built upon previous investigations by third parties to develop a targeted investigation design to infill previous gaps in knowledge. Data collected were focussed on obtaining critical input parameters for subsequent risk assessment and information required for practical development of remediation techniques.

Detailed Quantitative Risk Assessment (DQRA)
DQRA was undertaken for quantification of risk to both human health and the local water environment (groundwater and surface waters) in the proposed post-development case.

The complex contamination profile and specific conditions prevailing post-remediation necessitated the development and validation of novel approaches in the human health DQRA to determine the risk posed by contaminant vapours. These novel elements were integrated into the UK best-practice framework for undertaking DQRA and their validity confirmed by cross-calibration with other methods.

The water environment DQRA was based upon well-established modelling approaches taking due account of site-specific evidence for contaminant biodegradation in groundwater. This allowed the development of proportionate and efficient remediation objectives for mitigation of this risk.

Remediation Technology Development
Laboratory testing methods were developed in collaboration with Sirius’ analytical laboratory partner to enable specific testing of the performance of a range of potential remediation methods for the site. This included the application of novel test methods for vapour transport and solidification-stabilisation treatments that informed the subsequent remediation options appraisal.

Remediation Options Appraisal
Sirius undertook a full remediation options appraisal to develop an integrated remediation approach for the site. The appraisal made use of published and in-house test data for relevant remediation methods and included a sustainability assessment in line with the SuRF-UK guidance to identify the most environmentally and economically effective solution for the site.

Remediation Strategy
Sirius developed a detailed remediation strategy for the implementation of the identified remediation approach identified by the options appraisal process. This included the application of a geocomposite liner-based engineered capping layer, the use of solidification-stabilisation, the recovery of free-phase organic liquid contamination and the use of Monitored Natural Attenuation (MNA) for long-term management of residual contamination in groundwater. Full methods and criteria for remediation verification were specified for all elements of the work.

The activities defined in the strategy were taken forward for implementation by Sirius during the remediation phase of the contract.

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