Highways Management Consortium (HMC) was awarded the contract for improving the busiest trunk road in Scotland in late 2008. The works involved bringing the existing Stirling to Glasgow trunk road up to motorway standard. After consultation with the client, The Invasive Plant Company set about mapping all the infestations on the proposed new route of the improvement works. There were a number of areas of Japanese Knotweed discovered along the carriageway totalling just over 1,000m2 with a number of Giant Hogweed stands also present. Once the areas had been mapped IPC, arranged a series of meetings with the Client and designers to develop a remediation strategy to minimise excavation and impact on the Clients improvement works.
The remediation strategy involved a combination of herbicide treatment, excavation, sifting and burial and partial excavation with the use of root-barrier geotextiles. These methods reduced the volume of material leaving site by over 99% and in turn was far more economical and sustainable than removal to landfill of all contaminated soils. Following agreement of remediation strategy with the client, IPC met with the Scottish Environmental Protection Agency (SEPA) to consult with them on processes and findings. Thanks to IPC’s management plan,agreement with SEPA on the progression of the project was reached within one day and IPC could then move on to the implementation stage.
Works commenced in line with HMC’s programme in Condorrat around a road bridge that was due to be demolished and replaced later in the year. Excavations continued around the bridge for 4 weeks where all Japanese Knotweed material was removed to another part of the site for second stage treatment. The quick removal of the contaminated material enabled the client to complete the bridge demolition early and continue with the replacement bridge over the A80 ahead of schedule.
The second stage treatment involved sifting of all arisings in order to remove the Japanese Knotweed root material (rhizome) from the soils. The rhizomes were then sent to a licensed landfill while the sifted material was buried at a depth on site and capped with clean material. All burial chambers were surveyed to record their exact location for future monitoring and validation. This process was repeated over the whole site and all excavated material was transported to the treatment area for sifting and burial. In total, IPC removed over 3,200m3 of contaminated soils to the treatment area. The proportion of that material sent to landfill equated to 30m2, less than 1% of the total volume. If IPC had sent the full 3,200m3 of material to landfill, cost to the client would have been in excess of £900,000. In addition, this reduced the number or vehicle movements around the local area in what still is a high profile project for Scotland.
Highways Management Consortium (PFI).
Invasive Plant Company
For more information on this project, please contact, Conor Leyden