INNSA Standard 5 - Removal of Japanese Knotweed from Soil or Contaminated Material

The physical removal of Japanese knotweed rhizome relates to the separation of soil in order to allow the manual or mechanical removal of Japanese knotweed rhizome for disposal off-site thereby significantly reducing the amount of material taken off site. This system is suitable for sites which do not have time for longer term solutions and where space is at a premium. This system often utilises bespoke machinery specifically designed for the processing of materials into two or more fractions.

The treatment of soil or site material in this way is covered by the Environmental Permitting Regime and requires either a ‘bespoke permit’ or Standard Rules permit to be deployed on the site www.environment-agency.gov.uk/business/topics/waste/32160.aspx Permits can be obtained through the Environment Agency and the minimum requirement is “Standard rules SR2008No27 - mobile plant for the treatment of soils and contaminated material, substances or products”. In order to obtain the permit a suitably qualified WAMITAB COTC will be needed either as an internal member of staff or external consultant.

The remediation position statement Operational instruction 226_06 issued by the Environment Agency in November 2010 allows for the small scale treatment of soil without a permit provided the total quantity requiring treatment does not exceed 1000m³ and provided that a number of conditions are met including notification of the intention to undertake the work to the local EA office 5 days in advance.

Prior to any works being undertaken a full Japanese knotweed management plan (JKMP) should be prepared and authorised by a suitably qualified and experienced professional. The area of Japanese knotweed infestation should be suitably demarcated to prevent access and disturbance by site traffic and operatives. Disturbance, especially during inclement conditions, may lead to further cross-contamination. At this time a suitable static “screening zone” should be identified, this area should ideally be fenced from the main site and located on a solid area within close proximity to the Japanese knotweed infestation.

Where possible, excavation should take place from outwith the area of infestation to prevent plant tracks or tyres coming into contact with Japanese Knotweed contaminated soil. When working on large infestations or tight sites, this may not be possible. In this scenario, consideration should be given to laying a temporary blinding layer of suitable material or sacrificial root-barrier to prevent contact between Japanese Knotweed material and plant. As a last resort, plant and machinery coming into contact with Japanese Knotweed contaminated material should be thoroughly inspected and decontaminated by a suitable qualified person prior to further movement on site.

Excavation should proceed to the extent of rhizome network. When supervised by a suitably qualified person, the volume of excavated material can be significantly reduced compared to Environment Agency guidelines. On completion of excavation, further material should be loosened and inspected for presence of Japanese Knotweed material.

During the excavation process, removed material should be transported to the screening zone in manageable quantities as stockpiling of material to be processed in inclement weather may lead to delays or render the material unsuitable for screening in extreme circumstances. Where all Japanese knotweed requires removal prior to screening commencement, stockpiles should be protected with a waterproof covering.

Material passed through the screening machinery will be split into several fractions of material, typically oversize, midsize and fines. The material will then pass through a secondary system which will enable a mechanical or manual removal of rhizome from the soil which will subsequently be segregated in sealed containers ready from removal from site.

Upon completion of the screening process and when no further Japanese Knotweed material is encountered, the excavation may be prepared for backfilling or subsequent works. It is essential that any screened material which has the possibility to contain small fragments of rhizome is suitably managed by either the specification of a capping layer or the storage in an area which can then be monitored and treated with herbicide if necessary. In all cases it is recommended that a herbicide monitoring regime is implemented following any excavation works in the event that any small fragments of Japanese Knotweed rhizome have been overlooked. Suitable herbicides applied by qualified persons will prevent any small rhizome fragments from becoming re-established.

The final depth of rhizome penetration and amount of material processed may vary dependent on ground conditions and porosity. It is essential that all material is removed and screened unless it is proposed that a suitable root-barrier is to be subsequently installed.

Japanese Knotweed is listed on the Wildlife and Countryside Act 1981 as amended. As such excavated material to be transported offsite is considered a controlled waste. It is essential that a complete duty of care and waste transfer paperwork is in place to confirm material has been managed in an appropriate manner. Furthermore any persons transporting Japanese Knotweed soils must be a registered waste carrier and a copy of the license should be presented to the waste producer prior to works commencing.

Any landfill operator must be licensed to accept Japanese Knotweed and it is the waste producers’ responsibility to ensure that the contaminated material is transported and disposed of correctly. Records of how the material was transported must be kept in the event that the Environment Agency wishes to verify the wastes final location.

Further information on your responsibilities in relation to waste can be found at; http://www.environment-agency.gov.uk/business/topics/waste/default.aspx

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