Excavation and Relocation of Giant Knotweed

Excavation and Relocation of Giant Knotweed

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Japanese knotweed treatment on commercial site

Japanese Knotweed Ltd were invited to tender for the removal of Japanese knotweed, Giant knotweed, and Himalayan balsam for a project to create a link road to reduce traffic congestion and improve traffic flow which lay within the boundary of two local authority areas.

We initially completed a desk based tender using information provided by the client which included scope of works, line boundary drawing, core works overview, Environmental statement, and ecology report.

Pre-Award Meeting

We were very pleased when the client subsequently invited us to meet them for a pre-award meeting to discuss the project. We were advised that initial works required only the excavation of the Giant knotweed, which was impeding the next phase of site works. The Japanese knotweed would be dealt with under a later phase of works, and the Himalayan balsam fell outside the proposed works areas with no immediate remediation required. Additionally, to carry out the works we were required to have Constructionline Gold accreditation.

We immediately recommended to our client that they cordoned off the knotweed areas to prevent accidental disturbance and spread prior to remediation works. The plants possess underground rhizome (stems) that spread out beyond the above-ground visible extend of the plant. It is therefore recommended, where possible, that a temporary barrier is erected at a distance of 7m and no less than 5m from the visible plants. Although rhizome spread is typically 3m or less, it can sometimes be more, and a 7m exclusion zone is a good fail-safe recommended measure.

Invasive Weed Site Survey

A thorough walk over of the site was undertaken to identify the presence, locations and extent of Japanese knotweed, Giant knotweed, and Himalayan balsam growth. The survey was undertaken in accordance with current good practice published by the Property Care Association (PCA, 2018) and Royal Institute of Chartered Surveyors (RICS, 2012)

The survey area comprised of bare ground, semi-improved grassland, and tall ruderals. Canals formed the northern and eastern boundary and a brook was located along the boundary to the west. The remainder of the survey area was surrounded by industrial, residential, and commercial land.

Although the survey was conducted during the winter, the areas of invasive species comprised of mature and expansive growth making identification easier via the presence of previous seasons' brown desiccated stems. The area of site possessing Japanese knotweed and Giant knotweed totalled 1267m2, all of which displayed mature growth.

Invasive Species Survey
Image 1: Giant Knotweed Identified During Survey
Invasive Species Survey
Image 2: Survey Site Plan

Invasive Weed Removal and Treatment

Based on the proposed change of land use plans, we recommended excavation of all Giant knotweed areas, with excavation of the Japanese knotweed planned for a later phase of works. Undertaken correctly, excavation can immediately eradicate the plant from an area, allowing for free unimpeded main site works to be commenced on completion. Excavation removes the above ground plant as well as all the underground rhizome (plant stem) elements.

We were advised that the preference was to deep bury the excavated knotweed on-site using a cell-burial methodology. However, we assessed waste disposal options with the client and it was agreed due to the levels of ground water and available space on site, that the preference was to relocate the knotweed waste instead. This would entail full excavation and relocation of the waste to a suitable area of the site, away from proposed works area, where it could be formed as a bund and treated long-term with herbicides.

Invasive Species Survey
Image 3: Excavating Giant Knotweed to be Relocated to the Bund

We recommended the relocation bund did not exceed 500mm in height to improve the effectiveness of the herbicide treatment, which required an area of nearly 6000m2 for the location of the bund.

Prior to starting work on the site, we provided and agreed with the client a full Method Statement and Risk Assessment (RAMS), which is required for every site we work on and any type of work we do, be it excavation or herbicide treatment.

A 22-tonne excavator was used to carefully excavate the knotweed from source and transfer the contaminated waste into Articulated Dump Trucks (ADTs). The ADTs moved the knotweed soils to the designated bund area, whilst under the watching brief of our Site Supervisor, to ensure there was no waste spillage in transit. The knotweed contaminated waste was received at the relocation area by another excavator, which consolidated and graded the contaminated waste to form the low profile bund.

Himalayan balsam can spread prolifically and although outside the immediate scope of works we recommended in-situ herbicide treatment to start controlling the spread of this highly invasive plant. Works involve either chemical treatment, cutting or pulling of the plants, prior to them dispersing seed in late summer. Himalayan balsam can take many years to control due to repeat germination from previously dispersed seed in the surrounding soils ("seed bank"). Unfortunately, where Himalayan balsam is present on stream/river banks, re-infestation of the area by seed arriving from upstream plants remains an ongoing risk.

Land Remediation Tax Relief

As the client opted for onsite treatment of the knotweed, which provided a sustainable remediation process, Land Remediation Tax Relief (LRTR) could be claimed for the project. LRTR can provide 150% tax relief to help fund remediation costs.

Works Completion

The excavation and relocation works for the Giant knotweed took just over two weeks to complete.

All large plant and equipment was thoroughly cleaned on completion using a pressure washer to ensure all invasive weed contamination had been removed.

On completion, we provided our client with an updated Knotweed Management Plan detailing all works undertaken, including the location of the knotweed bund. We will herbicide treat the Giant knotweed bund for 5 years, with the client additionally opting for a 10-year Insurance Backed Guarantee, meaning all works are covered by guarantee until 2034.

Our client was very happy with the professionalism and expertise we had shown in approaching the project and undertaking the works, and left us a very positive review on Trustpilot.

Invasive Species Survey

We look forward to our return to site when the client is ready to undertake the excavation and removal of the Japanese knotweed for phase 2 of the project.

Invasive Species Survey
Image 4: Completion of Works Site Plan

Purple Areas
Excavated Giant knotweed stands

Green Areas
Himalayan balsam stands to be herbicide treated

Orange Dotted Line
Relocated Giant knotweed bund, to be herbicide treated

COVID-19 Procedures

These works were undertaken during Covid-19 lockdown. Social distancing was maintained at all times. Toolbox talks and site inductions were held outside, rather than in the site office. The usual sign-in book at the site office was replaced with a rollcall performed by our Site Supervisor each morning which reduced contact with possible Covid-19 contaminated items.

Trust in Japanese Knotweed Ltd, the UK’s Experts

We are the UK's trusted Japanese knotweed treatment and remediation company with a proven track record in working successfully for local authorities, developers, construction companies and private landowners. Our highly knowledgeable and skilled staff provide a comprehensive service and are committed to providing the highest level of customer care.

We provide Japanese Knotweed Surveys and Knotweed Management Plans, which include immediate excavation and/or long-term chemical treatment options with Insurance Backed Guarantees. Our remedial methods are tailored to each site and provide sensible and efficient eradication solutions to meet all requirements.

We are the UK’s largest dedicated Japanese knotweed and other invasive species treatment and removal company with PCA accreditation. We offer a range of services to both residential and commercial clients including:

If you suspect you have a Japanese knotweed problem, call us on 0333 2414 213 or email us at contact@knotweed.co.uk.

*Surveys on mainland England, Wales and Scotland are free, however if we find the property not to be affected by Japanese knotweed there is a charge of £140 +VAT and an accompanying findings verification report.

Get in Touch

We want you to know exactly how our service works and why we need your contact details. Please state that you have read and agreed to these terms and conditions before you continue.
Form by ChronoForms - ChronoEngine.com