Investigations in 2004 identified Japanese knotweed, which can crack through concrete and overpower native plants, spread across around two per cent of the east London site. Specialist contractors were brought in last year and have planned how to tackle the plant once access is gained to affected areas.
Following the spraying with herbicides over the last year, this month workers started cutting the dead knotweed canes concentrated on the site of the Velopark and beside the Aquatics Centre.
ODA Chief Executive David Higgins said:
"Cleaning up the Olympic Park site is a challenging job and we're starting with one of the toughest plants in the world.
"Japanese knotweed suppresses native plants and damages buildings if not tackled. It is only on a small proportion of the site, but tackling it now, well ahead of the planned start to building works, is the next step in the transformation of this part of east London.
"Our thorough clean-up programme will create of the new biggest urban parks in Europe in the last 150 years, fit for new and existing communities."
Under the Wildlife and Countryside Act it is an offence 'to plant or otherwise encourage' the growth of Japanese Knotweed. The ODA is taking a clean and cautious approach to cutting, transporting and incinerating the dead canes. The soil will then be treated to eradicate the resilient root system.
A range of treatments will be used to ensure construction remains on track including, where necessary, digging out soil and treating it elsewhere on site. Almost all treated soil will be reused on site although a small amount is likely to be removed.
Tackling Japanese knotweed makes up a small part of the established remediation and demolition budget and is not adding to the overall ODA budget announced earlier this month.
Contractors have dug over 1300 bore holes and investigated three-quarters of the site and to date have found nothing unexpected. Investigations are continuing and the full clean-up starts this summer when the full site becomes available.
The clean-up (remediation) programme on sites of the main venues is on track to complete before construction begins in 2008.
Notes to Editors
A 2004 survey identified Japanese knotweed in patches across the Olympic Park site with concentrations along river and canal banks and on the Velopark and beside the Aquatics Centre site.
Several methods will be used to treat contaminated land depending on the location, final use and size of the area affected and when the land is needed for construction. This flexible approach is the quickest and the most cost effective:
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- Spraying with appropriate herbicides has been taking place over the past year.
- The surface knotweed will be cut, placed in a skip and incinerated using an expert, safe and clean system to prevent spreading.
- Where possible and particularly near water, as Japanese knotweed spreads via watercourses, the soil will be sprayed with a suitable and safe herbicide.
- Away from water knotweed may be buried, excavated or sprayed. If excavated the soil with be treated with methods that may include maceration and/or burying within a special protective barrier to prevent regrowth.