The £1.86-billion Mersey Gateway Project, a 2.3-km, six-lane toll bridge made of reinforced concrete and supported by steel cable spans the River Mersey and links the towns of Widnes and Runcorn, thereby connecting the motorway network in north Cheshire with Merseyside. RemedX was appointed as the preferred remediation contractor to support the main contractor with the design and site implementation of all soil remediation activities and water management on-site associated with the project. Specifically, new embankments, junctions and slip roads linking the road networks required significant land acquisition in an area that was previously used for heavy industry and where a range of contaminants, such as total petroleum hydrocarbons, arsenic and cyanide, remained.
For the soil remediation and to maximise the reuse of material on-site, RemedX undertook extensive bench and field-scale trials during the design stage to provide the regulators with sufficient reassurance that the proposed remedial solution was feasible and that long-term leaching of contaminants from soil could be reduced to sustainable levels where the risk to controlled waters was negligible.
The site-wide remediation solution proposed treating contaminated soil and water using a range of methods. Contaminated water from across the entire scheme was collected and transported to a centralised wastewater treatment plant. Here, the treatment comprised elements of suspended solids settlement, dissolved-phase contaminant filtration using activated carbon and physical treatment using aeration. Soil from across the scheme was physically screened to remove oversized materials and then chemically tested to determine the reuse suitability of any material batch. The assessed and pretreated materials were then subjected to a bespoke, innovative stabilisation and solidification process for hydrocarbons and arsenic-contaminated soil using geochemical and hydraulic binding agents. The RemedX stabilisation and solidification process enabled the reuse of oversized materials to improve the soil’s geotechnical condition, thereby making it suitable for placement in the embankments.
Owing to our early involvement and close working relationship with regulators, we saved almost 100% of the excavated soil for on-site reuse. Our actions minimised the import of natural aggregate, which reduced transport costs, saved money and lowered the project’s carbon footprint.
This project was a Brownfield Briefing Awards 2020 winner for Best Re-use of Materials and Best Infrastructure Project.