On development sites, there is always interest in on site solutions, which manage the knotweed on site, while permitting development to happen. There a number of solutions approved by the Environment Agency in their Code of Practice, use of these may permit the developer to claim Land Remediation Tax Relief.
1) On site cell burial. Subject to certain criteria, Japanese knotweed contaminated soils may be buried on site. This can be cost effective and if managed correctly can be very effective.
2) Stockpile/bund and herbicide treatment. The knotweed contaminated soils are re-located to an area that will not be developed, spread over an area, fenced off and treated under an herbicide programme.
3) Reduced level excavation and installation of root barrier to formation levels. Another approved technique, this method may involve some material going off site (or of course a smaller cell burial or stockpile could be used. If material goes off site than the tax relief may not be claimable. Where the solution is all on site, than the developer may submit a claim for the tax relief.
There are some other onsite solutions which may be used; these include the sieving of soil or sifting. Sieving involves the passing of the soil through a mechanical sieve; sifting is the hand removal of large pieces of knotweed, by running the material through a conveyor belt. To our knowledge and experience of these techniques, neither of them will remove 100% of the knotweed material from the sifted/sieved soil. These techniques are useful in that the soil may be used on site for landscape purposes, as long as the soil is controlled during the building process (i.e. not mixed with clean soils or moved unnecessarily) and the resulting knotweed re-growth is subject to an herbicide programme, until eradication is achieved. The soil should therefore be handled under the Environment Agency’s Code of Practice for Managing Japanese knotweed on Development Sites. The use of the sieving/sifting technique is therefore somewhat limited in practice, as it does not reduce the volume of material to manage in anyway nor does it de-contaminate the soil.
Herbicide programmes are perhaps a classic case of onsite solutions. Essentially an herbicide is used to treat the knotweed until eradication is achieved. This is normally a period of 3+ years. As the Code of Practice states ‘You must not see the lack of regrowth as evidence that the Japanese knotweed is no longer alive.’ This is because Japanese knotweed readily enters a state of dormancy, which may be induced by the inappropriate use or selection of herbicides. However a correct programme set in place and carried out by trained staff has the potential to achieve eradication. Such programmes are relatively cheap to carry out and may permit the claiming of Land Remediation Tax Relief.
Wreford Limited has substantial experience of finding and carrying out all approved solutions and tailors the solution to the site, not the site to the solution.
