Where there is space on-site to accommodate a cell-burial this method provides instant eradication and a sustainable remediation process.
Onsite Burial of Japanese Knotweed
Legislation and Environment Agency (EA) guidelines permit the burial of Japanese knotweed to the same site from which it originated. However this should be done in accordance to the EA 'The Knotweed Code of Practice' 2013, which allows for either a 5m deep burial (infrequently feasible) or 2m deep burial. If buried at 2 metres deep the buried material must be encapsulated in root barrier, this is known as Cell-Burial.
We undertake the excavation of Japanese knotweed either fully or to a reduced level (see 'Dig n Cap' page). The excavated knotweed material is then buried on-site in a suitable location: Burials are prone to a certain amount of future movement (settlement) and it is therefore recommended they be located beneath areas of soft landscape (i.e. Public Open Space) rather than under hard standing or structures where possible (although this can be done as long there is suitable support engineering, such as compaction, to alleviate the settlement risk).
We use a method of works which allows for the knotweed material to be buried so it is fully encapsulated in knotweed root barrier on completion. The top of the encapsulated knotweed (the cell) will need to reside at least 2m below finished ground levels (unless authorised differently by the local EA officer). The depth of 2m is a pre-caution against future human or burrowing animal disturbance of the cell.
The Knotweed Management Plan (KMP) should be used to record the position of the cell-burial, with this being marked upon an as-built site drawing. This will help prevent potential future disturbance of the burial location. If these works are part of a site development project the KMP should then be included in the Operations and Maintenance (O&M) Manuals.
Burial of Other Contamination
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 spoil containing Japanese knotweed material, and not any other contaminant, is to be buried. This verification is normally achieve via provision of laboratory soil analysis results from the site.
If other contamination is found further analysis may be required (such as WAC testing to check for leachate properties of the contaminate) prior to acceptance to bury. In some cases burial on-site may be ruled out due to levels and/or types of other contaminates present.
Land Remediation and Tax Relief
Disposing of the excavated knotweed on-site is sustainable option for which Land Remediation Tax Relief (LRTR) can be claimed. A system of LRTR has been in place for several years, but the complexities of it, 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.