The former industrial site, planned for development during 2011, had a history of established knotweed. In 2009, a company claimed that their one-year programme would eradicate knotweed from the site and provided a five-year warranty.
Technical consultants White Young Green assessed the knotweed situation in early March 2011 and concluded:
- In the worst case scenario, the eradication may not have been achieved on any of the knotweed.
- A single follow-up visit to confirm that the eradication was successful was insufficient evidence.
- The warranty was only likely to be honoured if the area was undisturbed for five years.
Kier Western, the preferred tenderer for development of a new Sainsbury's store, invited Elcot Environmental to assess for an approved cost for a management plan that would enable construction to commence on schedule.
A site visit by Elcot Staff revealed live knotweed emerging from some of the treated areas and, significantly, knotweed shoots outside the treated locations in an extensive area. Following appraisal of the evidence gathered on site, Elcot provided a fixed cost management plan.
At the first opportunity, Elcot revisited the site and carried out a futher detailed site monitor and initial treatment, finding an increased number of new knotweed shoots in the location predicted.
A sift operation ran concurrently and sifted material stockpiled for diposal – some-off site and a portion to be buried on-site.
The whole dig, sift and stockpile operation, and the partial bury operation, was completed around 3 weeks after commencing, working around live gas services and co-ordinating operations with the demolition of unstable boundary walls and groundworks being carried out by other trades.
Elcot had advised that the treatment of off-site knotweed on a nearby canal should be undertaken to protect the site from risk or recontamination. The landowner's permission was obtained and Elcot added this to the monitoring program at no extra cost.
To date, no knotweed has been seen other than in areas on the perimeter or offsite, where management was by treatment only.
Elcot provides proactive monitoring for a minimum of four years, and two years beyond the last treatment and last incident of knotweed, before making a claim to have eradicated the knotweed.
Following this point of proof, another 10 year warranty against the return of knotweed is provided, protected by a paid-up-front, insurance-backed guarantee.