Author: Thomas Hicks BSc (PA1, PA6)
Site Size: 2500 m2
Location: East Midlands
Techniques: Excavation, Membrane barrier
Knotweed Services (UK) Ltd were contacted by the client to organise a site survey of a development site. Another knotweed company had begun works already but the client decided to move company.
The developer aimed to continue with their schedule but with a slightly revised time plan. They plan to build 10 houses on a previous brown site within 2 years. Consequently, we aimed to eradicate the knotweed from the site within 3 months, minimising disruption.
The first and arguably most important stage of any successful management plan is to assess the extent of the problem. Until this was fully understood we recommended to the clients that site works ceased.
Once we identified the above ground Knotweed we fenced of the infested areas so that other site works could continue. This prevents disruption to tight de-velop schedules. In addition to the fencing all contrac-tors working on site were given a briefing by our staff on Japanese Knotweed. Areas covered included how to prevent it spreading and a health and safety brief.
The mapping stage of our plans is crucial to preventing spreading of the Knotweed. We created detailed maps with clear working routes and areas for stockpil-ing contaminated and non-contaminated soil (figure 2).
The next key step was communication with the client. We made sure that we fully comprehended the cli-ent’s proposals and timelines as this dictated the type of treatments we could undertake.
From this we were able to deduce that a supervised excavation and off-site removal was the most appropriate treatment option. All site operations (e.g. tree felling and excavation) occurring in the fenced zones were supervised by one of our trained operatives.
We then proceeded to excavate the infested soil (see above). The soil was transferred to the stockpile and then to removal trucks with retractable covers to pre-vent spreading to clear areas. Before leaving site all trucks tyres were treated with herbicide to create a chemical barrier. The waste was carted to a specialist contaminate waste landfill site. All working areas and plant used for the exaction were also treated after completion. This method provided a quick solution to Knotweed eradication which is why it was the most suitable for the client.
Specialist membranes were used across the site to pro-tect areas from future Japanese Knotweed growth. We used the Hy-Tex Root Barrier C3 (solar black).
Horizontal Barriers – The membrane barrier was in-stalled 2m under all of the proposed building and road footprints impacted by Japanese Knotweed. This pre-vents any dormant Knotweed from emerging in the fu-ture. The membrane will prevent Knotweed growth in the area for up to 50 years. The environment agency dictates this longevity since rhizome fragments can re-main dormant in soil for up to 20 years (Enviroment Agency, 2013).
Vertical barriers – For some areas (see yellow houses on map) Knotweed was found near the site boundary. Because the client did not have permission to treat this area full excavation was not possible. In these cases we in-stalled a vertical membrane. This prevents the lateral encroachment of Japanese Knotweed from the neighbouring land.
INSURANCE BACKED GUARANTEES (IBG’S)
Knotweed Services UK offer their insurance backed guarantees through Guarantee Protection Insurance Ltd (GPI). GPIs primary and founding product was IBG’s and they are in the industries leaders in Japanese Knotweed insurance. The package we recommended for this project is the is “designed to provide cover in the event that the insured remedial works fail, during the period of insurance, and the contractor has ceased to trade and is unable to honour claims on the written guarantee.” (GPI, 2017).
Enviroment Agency, 2013. The Knotweed Code of Pratice. [Online] Available at: www.naac.co.uk/userfiles/files/Japanese%20Knotweed%20Guidance.pdf [Accessed 07 11 2017].
Guranatee Protection Insurance (LTD), 2017. Japanese Knot-weed IBG. [Online] Available at: www.gp-insurance.co.uk/[Accessed 07 11 2017].
Hy-Tex (UK) LTD, 2015. Hy-Tex Root Barrier C3 (Solar Black). [Online] Available at:www.hy-tex.co.uk/docs/geotextiles/Root_Barrier_C3/r_rbc3_03.pdf [Accessed 07 11 2017].
|Specifications||Hy-Tex Root Barrier C3 (solar black)|
|Material||triple coated, twin reinforced, impermeable, polyethylene barrier membrane|
|Elongation||md 25% cd 20% [EN ISO 10319]|
|Puncture Resistance||4,500 [EN ISO 12236]|
|UV Stabilisation||400 kLy|
|Life Expectancy||> 50 years in natural soils with a pH between 4 and 9|