Excavation Options

If herbicidal treatment is not convenient in terms of timescale, Wreford offer a full range of options involving the excavation of Japanese knotweed. The 2006 Environment Agency Knotweed Code of Practice (“Managing Japanese knotweed on development sites”) puts the emphasis firmly on reducing quantities of waste removed to landfill. This is in line with Wreford’s standard operating procedures where we always ensure only knotweed material – and not clean soil – is excavated and removed from site. Quantities can be further reduced through the process of screening, if required.

Key to Wreford’s success – and the foundation of the new EA Code of Practice – is dispelling the dependence on the ‘7 x 3’ rule (excavating 7m wide by 3m deep) that some contractors still adhere to. This reduction policy has resulted in considerable financial savings for our clients, as well as relieving some of the environmental impact knotweed excavations inevitably cause. Reducing quantities reduces the number of lorries required on site and, where off-site disposal is involved, alleviates some of the pressure on the limited landfill resources in the UK by reducing the volume of material that needs to be buried at the landfill facility. All our excavation operations are backed by full warranties and guarantees of removal.

Excavation and Muckaway
The most common knotweed treatment solution, but also the most expensive. Knotweed is excavated, making allowance for rhizome spread, and disposed of via sheeted haulage vehicles to a landfill facility licensed to take Japanese knotweed material, in accordance with the Environmental Protection Act 1990, Duty of Care Regulations 1991. Post excavation, herbicide treatment may be required in certain circumstances.

It is important that excavation and muckaway (commonly known as ‘dig and dump’) be increasingly regarded as a last resort and therefore only utilised when more sustainable on-site treatment solutions are considered unfeasible. If current developments continue then landfill disposal of knotweed will become more and more untenable as a practical option. Therefore it is important to start getting in the habit of considering other ways of dealing with the plant now before the government forces the construction industry’s hand.

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 £48 per tonne by 2010 and £108 per tonne by 2015 (assuming the level of increase stays the same). Many developers have been able to reduce the expenditure of landfill disposal by applying for Landfill Tax Exemption, but this is about to change, as there are plans to scrap this Tax Exemption from 1st April 2010 - and the final date for applying for tax exemption is 30th November 2008.

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 will be transferred into LRTR instead. However, LRTR cannot be applied for if any material is to be disposed of off-site. This means that, as of April 2010 under current proposals, it may be impossible to obtain any kind of financial discount for ‘dig and dump’ operations.

The Government are also to launch the Strategy for Sustainable Construction during 2008, containing a number of proposed waste disposal targets for the construction industry to achieve through a series of voluntary agreements and initiatives. A target of a 50% reduction in the amount of construction, demolition and excavation waste (including Japanese knotweed) going to landfill by 2012 has been proposed, with an eventual target of zero landfill disposal for 2020.

This is why Wreford are committed to moving away from ‘dig and dump’ operations wherever feasible. But for the construction industry as a whole to successfully move away from landfill disposal, except as a last resort, knotweed must be identified before any works commence on site and more time must be allocated to its treatment.

Excavation and on-site burial
If certain conditions allow, it may be feasible for the excavated knotweed to be buried on site, encapsulated within specialist membranes. According to Environment Agency guidelines, the top of the burial cell should not be less than 2m below the finished site ground level. To prevent potential disturbance and re-infestation the burial site location should be recorded and any future landowners advised of its position. The local EA office Environment Protection Team should be informed at least one week prior to the burial activity so they can verify that only knotweed material (and not any other contaminants) is to be buried.

Please note that the creation of an on-site burial cell is subject to particular criteria and may not be suitable for all sites. Burial pits are prone to a certain amount of future movement and it is recommended they be located beneath areas of soft landscape rather than under structures that may crack or become dangerously uneven following settlement, unless suitable supporting structures are installed above the burial cell. The on-site burial option is not available where other contamination of the site requires compliance with waste management or other legislation unless it is carried out in accordance with that legislation.

Haulage and Tipping
If required Wreford Ltd can provide a stand-alone knotweed disposal service. Any removal of knotweed material from site will be conducted in accordance to all relevant legislation, Environment Agency guidelines and standard good practice. Wreford will utilise their landfill site contact network to ensure all knotweed disposal strictly adheres to The Environmental Protection Act 1990 and Duty of Care Regulations 1991.

Further excavation options, such as Relocation and Reduced Dig, are detailed on the Combined Methods page.