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Japanese weed proves to be a knotty problem for ODA

Land remediation at the Olympic Park has hit a hurdle early on with the revelation that the site is covered with fast-spreading 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 onsite at the moment.' Huck's firm is treating weeds on Murphy's underground tunnelling project. Contractors working onsite confirmed that the problem was particularly prevalent around the waterways and railways that crisscross the park.The ODA played down the problem and said that the knotweed covered just 4ha or 2% of the 200ha park and that a method for treating the knotweed 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 fill site (dig and dump) is the most common method of removal. Alternatively, the weed may be buried on site, beneath a geotextile membrane and 5m of clean fill material.Although much quicker, both are expensive options. Excavation costs for a 50m2 infestation costs, on average, £160,000, compared with £4,000 using spray. On top of this landfill charge is £70 per tonne.An ODA spokesman said the control of knotweed was accounted for in its budget and spraying would be used as a treatment where possible.

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