Where no other methods of on-site management of Japanese Knotweed are suitable for a particular site, a controlled excavation and removal off site to a licensed facility (Dig and Dump) may be the only viable option.
Prior to works, 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. Furthermore it is essential that the waste is classified by the landfill operator prior to the material being exported from site. This can be done by providing a chemical analysis of the soil, which needs to be carried out by a UKAS accredited lab and transported under controlled conditions. This information may be available from the Site Investigation Report for the site.
Where possible, excavation should take place from out with 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.
Consideration should be given when moving the excavated material from excavator to proposed receptacle so that material is not lost during transport. Implements should be under-filled to prevent this scenario.
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.
When no further Japanese Knotweed material is encountered, the excavation may be prepared for backfilling or subsequent works. The final depth of rhizome penetration may vary dependent on ground conditions and porosity. It is essential that all material is removed unless a suitable root-barrier is to be subsequently installed. 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.
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