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Japanese weed proves to be a knotty problem for ODA


LAND REMEDIATION of the Olympic Park has hit a hurdle early on with the revelation that the site is covered with fastspreading Japanese Knotweed.

Speaking at the launch of the planning application for the park on Tuesday, EDAW principal and masterplanning team leader Jason Prior said: 'There's tons of the stuff on site. You need a machete to walk through certain parts.' Ground maintenance specialist Ground Control criticised the Olympic Delivery Authority (ODA) for its slow action in tackling the weed. 'People I know working with the ODA wanted to start spraying last year, but the ODA hasn't decided what it wants to do, ' said senior contract manager Neil Huck.

He said there is nothing being done to tackle the infestation.

'We know we are the only ones doing anything on site at the moment.' Ground Control is treating weeds on Murphy's underground tunnelling project.

Contractors working on site confi rmed the problem was particularly prevalent around the waterways and railways that crisscross the park.

The ODA played down the problem and said the knotweed covered just 4ha or 2% of the 200ha park and that a method for treating the weed was being devised.

One option is to spray the weed with herbicide, but this can only be carried out between March and September, and can take up to four years to prove effective, depending on the type and strength of chemical used.

Excavation and removal to a regulated land fi l site (dig and dump) is the most common method of removing knotweed.

Alternatively it may be buried on site, beneath a geotextile membrane and 5m of clean fill material.

However, both are expensive options. Excavation for a 50m infestation costs, on average, £160,000, compared with £4,000 using a spray. On top of this Landfill charge is £70 per tonne.

'I think they will go for the expensive dig and dump option, ' said REC senior ecologist Haney King.

'Construction projects always leave Japanese knotweed as an afterthought and particularly on this project's timetable they'll want the fastest option.'

An ODA spokesman said that the control of knotweed was accounted for in the Authority's budget and spraying would be used as a treatment where possible.

According to the Environment Agency, Japanese knotweed can grow at a rate of 20mm per day and costs the UK £1.56bn per year to control.

It can flourish anywhere and penetrate minute cracks in mortar, concrete and asphalt, which in turn can lead to structural damage.

Contractors Nuttall and Morrison are responsible for the full-scale remediation, which is due to begin in July once all the land has been compulsorily purchased.

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