HMP Holloway knotweed removal
By Jennifer Holmes

HMP Holloway knotweed removal

PROJECT EXAMPLE: Removal of knotweed to allow for change of land use

In 2015 HMP Holloway contacted us because they suspected Japanese knotweed was growing between the site perimeter boundary and the wall of the prison. Having surveyed the site we accurately identify knotweed, established the risks it presented and assessed feasible remediation solutions. In total we located 9 separate areas of knotweed on site and the presence of knotweed off-site in an adjoining property.

To gain control of the problem and stop any further spread we were instructed to provide a 5-year herbicide treatment programme on-site and the treatment of knotweed where present in neighbouring property.

change of use

In 2018 the prison was closed and sold for development into housing. Due to the change of plans for the site, the in-situ herbicide control of knotweed was no longer a viable remediation option. To remove the knotweed contamination from the site and allow for free unimpeded development, the knotweed required excavation. We re-surveyed the site and assessed the proposed site development plans against the locations of knotweed in order to put together a remediation plan to remove the knotweed prior to demolition of the site. In preparation for the works a site-specific Knotweed Management Plan, Method Statement and Risk Assessment were created and reviewed and accepted by all parties involved in the works.

The excavation project was one of 186 excavations projects that we successfully completed that year. Our site supervisor (CSCS, CPCS and PCA qualified) over-saw a direct team of trained CPCS machine operators in the complete excavation and removal of all knotweed. The works required the expert identification of the above and below ground (rhizome) elements of the plant to ensure complete removal, while only excavating the soils containing the plant.

Due to restricted access between the prison wall and site perimeter, the excavated knotweed was double handled using part filled dumpers and relocated past a restricted access point (pinch point) to a location on site where it could be stockpiled in a controlled location and loaded to road-going 8-wheeled cart-away lorries (licensed waste carriers). The excavated knotweed waste was removed from site as controlled waste and disposed at a licensed landfill facility.

Recorded waste

As with any excavation project we maintained a waste tracking record (including copies of all haulage and landfill tickets) which was provided to the client within the Knotweed Management Plan document updated on completion of the works to provide a record of activities undertaken.

Excavation of knotweed provides instant eradication of by removing all elements of the plant from the site. Once the project was completed, we provided a guarantee of works on the excavated areas. The guarantee was protected via a third-party guarantee insurance.