A project as vast and complicated as the Mersey Gateway bridge must also adhere to strict environmental standards. Merseyside has a long history of extensive heavy industry, and land in the Gateway area could have potentially contained contaminants. RSK’s cohesive work from its various businesses minimised the financial impact of any contaminated materials and prevented any programme delays. The key to achieving this was to maximise the economic reuse of soil: testing identified untreated soil suitable for reuse, for example, in engineered earth structures, with the remainder treated on-site.
The remediation approach was developed and refined through bench-scale trials using our specialist geochemical laboratory to understand the contaminant mineralogy and geochemistry and to determine appropriate mix designs for each type of impacted material. For total petroleum hydrocarbon contaminated soil, specialists blended lime, cement and pulverised fuel ash. For arsenic-contaminated soil, the preferred mix included hydrous ferric oxide as a sorbent and magnesium oxide as a hydraulic binder. A full-time RSK contamination verification manager assured remediation worked to plan. We worked collaboratively with regulators, the Environment Agency and the local authority and with the contractor’s team to tailor the approach to the client’s specifications.
The local authority’s archaeological advisers approved our archaeological design. Throughout the 36-month construction period, specific teams undertook an archaeological watching brief and liaised with the scheme engineers and environmental coordinators to integrate the archaeological work into the construction programme. The archaeological monitoring covered excavations for the mobile scaffold-support construction area. No time was lost during the construction programme through archaeological works. The work supported the community engagement programme and provided artefacts and interpretive materials for display at the Mersey Gateway visitor centre.
Treating, testing, monitoring and training
Excavations required dewatering or simple pumping to remove inflows of surface water and groundwater. Owing to the contaminants in the ground, protocols were put in place to collect and treat this water, which was then suitable for discharging to the municipal sewage system. One of the hazards encountered with the excavated materials was asbestos in soil. RSK’s laboratory specialists tested the materials and advised on control measures. Later, we ran an asbestos awareness training programme for site personnel.
RSK played a significant role in collating huge amounts of environmental data relating to planning conditions and consents. It also provided radiation monitoring and advisory services in collaboration with the Radiation Protection Agency and Health Protection Agency. Envirolab, an RSK company, delivered a substantial programme of chemical analysis and soil and water testing throughout the construction period. A specialist team of four environmental clerks facilitated rapid decisions on environmental issues and provided pragmatic solutions offering minimum disruption to the programme.