A housing association instructed JKSL to complete a full Invasive Weeds survey of their site in Darlston, this site was planned for development to affordable housing 2015/16. Jonathan Harris met with the client onsite to discuss the development plans before completing the survey.
Mechanical remediation was the preferred option as the Japanese knotweed was located within the development footprint. Due to the constraints of the site, burial and waste management area methodologies were not considered viable. Instead, excavation to landfill and screening methodologies were explored with the client.
Screening proved to be the most economically viable option, initially estimated at over £6000 cheaper than alternative landfill option. With this considerable cost saving, screening was the preferred option by client.
The volumes of material that needed to be screened meant a medium screener was most suitable, however this took careful planning due to the area constrains of the site.
Sometimes with excavations we uncover some oddities, in this case underground voids caused by previously unknown buried concrete infrastructures. The rhizome network extended through these voids and in places reached depths greater than 4m below ground level. This resulted in an increase in the volume of material to be screened from an estimated 230m3 of material containing Japanese knotweed to greater than 500m3.
The screening methodology gave more flexibility with the increased volumes of material and saved the client £15k compared to excavation to landfill.