Japanese knotweed dig and cap

Dig and Cap

A fast and impressive remediation method achieving instant eradication, while minimising the volumes of excavated knotweed waste.

Reduced Level Excavation

On construction sites there is a maximum depth of excavation that is required before installations can begin. This depth is known as the construction formation level. The principle of the 'Dig n Cap' method is to remove the knotweed to formation level only, minimising the depth of excavation and the volume of contaminated arising waste.

The arising knotweed waste from this activity can either be removed off-site to a specially licensed landfill or disposed on-site via burial or relocation.

Capping

Following excavation any remaining knotweed contaminated ground needs to be capped with a specialist knotweed root barrier to prevent re-emergence of the plant from underneath. There are two specifications of root barrier: Porous and Non-Porous. The correct specification most commonly depends on the drainage (water percolation) requirements of the installation area. The root barrier should be bonded to adjacent structures and/or overlie the affected area to remove any risk of knotweed re-emergence from underneath. In some situations it may be necessary to install sand blinding layers over and/or under the root barrier to prevent puncturing under compaction (from the construction activity above).

The Knotweed Management Plan for the site should be used to make record of the location (and depth) of the root barrier cap on as built drawings for the information of others. This will help avoid accidental damage of the root barrier in the future.

Waste Volume Reduction

By undertaking this method of removal we minimise the waste volume by: (1) Excavating to a set depth only (2) Accurately identifying knotweed rhizome in the ground, so that only knotweed material and ground containing knotweed is excavated.

Disposal Option: Landfill

If the resulting waste is to be removed to landfill our waste reduction method will have resulted in considerable financial savings for our clients, as well as relieving some of the environmental impact knotweed excavations inevitably cause.

As well as the waste reduction being part of our on-going success, it’s also a foundation policy of the Environment Agencies 2013 'The Knotweed Code of Practice'. The most recent code puts emphasis firmly on reducing quantities of waste removed to landfill. This is in-line with our standard operating procedures where we always ensure only material contaminated with knotweed (and not clean spoil) is excavated and removed from site (when Japanese knotweed leaves a site is classed as controlled waste and must be handled and disposed of in accordance with the Environmental Protection Act 1990, Duty of Care Regulations 1991).

Disposal of Japanese knotweed at landfill is subject to Landfill Tax. Landfill Tax has been rising annually for the past few years, and it is set to continue to rise rapidly for the foreseeable future. In the Budget of 2007, the Chancellor of the Exchequer announced that standard Landfill Tax will rise from April 2008 by £8 per year, meaning it will reach £72 +VAT per tonne by 2013 and £88 per tonne by 2015 (assuming the level of increase stays the same).

Diposal Option: Onsite Sustainable Disposal

Disposing of the excavated knotweed on-site is sustainable option for which Land Remediation Tax Relief (LRTR) can be claimed. There are two forms of on-site disposal available: (1) Burial (2) Relocation. Both methods rely on sufficient space on-site to accommodate (1) A underground burial cell and (2) A stockpile/bund, respectfully. More information on these methods can be found on the 'Dig n Cap' and 'Relocation' pages.

A system of Land Remediation Tax Relief (LRTR) has been in place for several years, but the complexities of the system (along with the lack of suitable publicity) have ensured LRTR has rarely been applied for.

In the 2007 Budget, the Chancellor announced a consultation into improving the tax relief system and to help redress this situation, which suggested any savings gained from scrapping Landfill Tax Exemption (1st April 2010) will be transferred into LRTR instead. However, LRTR cannot be applied for if any material is to be disposed of off-site.

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