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Japanese Knotweed & The Environment Agency  

tel: 0333 456 7070
mob: 07950 259 905

Introduction

The Environment Agency has published guidance for developers on Japanese knotweed entitled 'Managing Japanese knotweed on Development Sites: The Knotweed Code of Practice' (the Code). This provides guidance on the legislation covering the handling and disposal of Japanese knotweed.

The Methods of Treating or Disposing of Japanese Knotweed

(i) Cutting Japanese knotweed stems

According to the Code, cutting knotweed stems is less of a risk than pulling them (as pulled stems often have the highly invasive crown material attached to them). Cut stems are safe once they have dried out and turned brown. The stems can be left on site after cutting if:
• the stem is big enough that it won' t be blown away by wind or traffic;
• there is no risk they can get into a watercourse
• the stem has been neatly cut near its base using a cutter, hook or scythe.

(ii) Burning

The Code advises that developers can use controlled burning of stem, rhizome and crown material as part of the programme to control Japanese knotweed. This means the material is less likely to survive and there is less material to bury or dispose of off-site. In its native area, Japanese knotweed grows on volcanic ash and around hot fumaroles, so it in inadvisable to rely on heat treatment to completely kill it. Burning must take into account any local by-laws and the potential to cause a nuisance or pollution. Developers should contact the Environmental Health Office of the relevant local council before burning. The Code states that developers must inform the Environment Agency's local area office, Environment Management Team, at least one week before any burial or burning activity.

Burning should be carried out in the open in accordance with a registered exemption as described in paragraph 30 of Schedule 3 of the WMLR 1994. This exemption must be registered with the Environment Agency and covers 'burning waste on land in the open if.....[it] consists of plant tissue'. To fall under paragraph 30, the waste must be burned on the land where it was produced and the total quantity burned in any period of 24 hours does not exceed 10 tonnes. The exemption also covers associated storage, which will allow the material to dry, which it is likely to need before it can be burned.

(iii) Treating with herbicide

Another method of eradicating the knotweed is to kill the pants with herbicide. This is the least expensive method but it can take at least two to three years to ensure that the knotweed is dead. Kill rates vary, depending on the type of herbicide, soil depth and how well established the knotweed is. Roundup Pro-Biactive is the most effective herbicide for most situations and is licensed to be used near water courses. It is a Glyphosate-based herbicide which can treat dense stands of Japanese Knotweed. Glyphosate is a systemic herbicide which acts by blocking a plant's enzyme system.

On some very extensive research sites in Cornwall, a ninety nine per cent reduction in knotweed has been achieved over three years using this herbicide. It is absorbed through growing leaves and stems where it is translocated throughout the plant and root network. However, not all formulations containing Glyphosate are approved for use in or near watercourses under the Control of Pesticides Regulations 1986.

The Control of Pesticides Regulations 1986 require any person who uses a herbicide or pesticide to take all reasonable precautions to protect the health of human beings, creatures and plants, safeguard the environment and in particular avoid the pollution of water. Anyone who uses a herbicide must ensure that they do not pollute the water environment and the use of herbicides in or near water requires approval from the Environment Agency.

Furthermore, it is important to note that material containing knotweed which has been treated with certain herbicides, may be classified as hazardous waste. The Hazardous Waste Regulations 2005 (HWR 2005) contain provisions about the handling and movement of hazardous waste. Consignment notes must be completed when any hazardous waste is transferred, which include details about the hazardous properties and any special handling requirements.

(iv) Burial of Japanese knotweed

Another method of dealing with knotweed is to excavate it and bury it beneath impenetrable barriers or plastic sheeting. Soil containing Japanese knotweed material and burnt remains of Japanese knotweed may be buried on the site where it is produced to ensure that it is completely dead. The Code advises that material buried on site on-site should be buried at least 5m deep. However, it also recognises that in some situations where burial is the preferred disposal method but it is not possible to bury Japanese knotweed to 5m, it may be completely encapsulated into a root barrier membrane cell. These cells may be placed under buildings, within cellar voids or in places that will not be disturbed. It is important that the deeds of the property show where these cells are located, to avoid damage in the future that could be caused, for example, by trenching to lay services. To avoid damage after it has been installed, the upper ' cell' surface must be covered with a capping layer, at least 2m deep.

If developers intend to bury knotweed on the development site they will need to consult the Environment Agency first to make sure that the material does not contain any other contaminant (such as herbicide) that may affect the quality of groundwater.

It is advisable to apply a non-persistent herbicide at least once to reduce the growth of infective material. It is important that a non-persistent herbicide is used, such as Glyphosate, because persistent chemicals will contaminate the material for a while. The period of time during which the herbicide is ' active' is described on the product label. Material cannot be buried during that period of activity. Burying material treated with a persistent herbicide may contaminate groundwater. If developers are in doubt whether the herbicide is still active, they should consult with the supplier of the product or the contractor who applied it.

(v) The bund method

Where local conditions mean burial cannot be used as an option, it may be possible to create a Japanese knotweed bund. A bund is a shallow area of Japanese knotweed-contaminated soil, typically 0.5m deep. The bund can either be raised, on top of the ground, or placed within an excavation to make the surface flush with the surrounding area. The purpose of the bund is to move the Japanese knotweed to an area of the site that is not used. This 'buys time' for treatment that would not be possible where the Japanese knotweed was originally located.

The Code advises developers that it is best to consider if a bund is needed when purchasing the site, and planning the building phases. It also advises that a bund needs the following:

(a) an area set aside for at least 18 months - 2 years for Japanese knotweed treatment. Deeper bunds may need longer
(b) local planning authority approval, if necessary, before creating a bund. It is advisable to emphasise the purpose of the bund, and how long it is expected to take to build when discussing the proposal;
(c) an area within the perimeter of the original site. Removing Japanese knotweed contaminated soil from a site will need a waste licence and disposal will only be permitted at licensed landfill sites;
(d) positioned away from watercourses (the Code advises at least 50m) and trees. If the bund is to be created on a site previously free from Japanese knotweed, clean topsoil from the bund area may be removed and used for landscaping purposes, perhaps in restoring the site where Japanese knotweed was excavated;
(e) temporary bunds should have a root barrier membrane layer to protect the underlying site from Japanese knotweed infestation. Permanent bunds on previously Japanese knotweed-free areas should also use a root barrier membrane layer to contain the material. If the site was previously contaminated with Japanese knotweed, there is no need for the root barrier membrane layer;
(f) not more than 1m deep, and preferably no deeper than 0.5m. Clearly, a large area may be needed to provide enough space for a bund, especially if infestations are scattered around the site or dominate a large part of it.

(vi) Excavation and Landfill Disposal

The most expensive method of eradicating Japanese knotweed is to excavate the soil and take it to an approved landfill site. The Code advises that wherever possible, Japanese knotweed should be treated in its original location and excavating Japanese knotweed should only be considered as a last resort, unless this is part of an on-site treatment method.
If Japanese knotweed and waste soil is sent for landfill either before or after any treatment, it must go to a landfill that is authorised to receive it. Basically, it should be disposed of in a licensed landfill site. Developers should notify their waste haulier that the waste to be removed contains Japanese knotweed. They should also contact the landfill site several days before any material containing Japanese knotweed is taken there to allow a suitable area to be prepared for its disposal. Developers should understand that they have a duty of care to make sure that the waste is disposed of properly and there is an ongoing liability until it is.

Any excavated soil from areas where Japanese knotweed has established must be disposed of at a licensed landfill site and not reused in further construction or landscaping. When disposing of contaminated soil it is essential that the landfill operator is made aware of the presence of Japanese knotweed and that the soil is not used for landscaping or restoration works at the tip site. To ensure safe disposal, contaminated soils must be buried to a depth of at least 5 meters.

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Japanese Knotweed Survey © Copyright 2011

Japanese knotweed survey, management, control, eradication & land remediation relief.
Areas include Staffordshire, Cheshire, West Midlands, Manchester, Birmingham & Stoke On Trent.

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