Advanced Invasives was engaged late in the construction phase of a £200 million brownfield development. While Japanese Knotweed was known to be onsite and on neighbouring land, ‘new’ growth appeared in areas that the funder’s experts had previously reported as clear. This raised questions about a breach of duty of care by the main contractor and responsibility for liquidated damages.
Brief
Dr. Jones was retained as an independent expert to:
Identify the original source of the Knotweed.
Evaluate the efficacy of historical Knotweed treatments applied to the site.
Determine the cause of the ‘new’ growth observed during the construction phase.
What we did
The team conducted an exhaustive forensic investigation of the 10-hectare site:
Physical excavation – found immature plants in ‘new’ areas attached to small-diameter rhizomes (roots) at shallow depths (c.20cm). In other areas, they found established growth showing symptoms of herbicide over-application.
Forensic document review – analysed several thousand pages of site reports, management plans, and drawings dating back over 20 years.
Historical mapping – used aerial photography to produce 12 site map ‘snapshots,’ tracking the evolution of the infestation over time.
Spatial analysis – proved that Knotweed had been present in over 40 locations (covering c.2 hectares or 20% of the site) for more than 25 years.
Key Outcomes
The investigation concluded that the ‘new’ growth was not a result of a new introduction, but a direct consequence of how the site had been managed historically and during current works.
Source identified – the spread was attributed to suboptimal treatment methods (such as cutting and the use of ineffective herbicides) which had left the plant viable but suppressed.
Construction impact – earthworks conducted during the construction phase had moved contaminated soil around the site, ‘activating’ the dormant Knotweed in previously unreported areas.
Liability shift – by proving the Knotweed was a long-term, site-wide issue that had been mismanaged for decades, the report provided the necessary evidence to navigate the complex claims of contractor negligence and liquidated damages.
Project value
£0 million
Sectors
Summary
Dr Daniel Jones provided critical expert evidence to determine the source of ‘new’ Japanese Knotweed growth that appeared in previously cleared areas on a £200 million industrial development. Through an exhaustive forensic audit – including the review of 20 years of site records, 12 historical mapping snapshots, and physical excavation – Dr Jones proved that the infestation was not a new introduction but the result of decades of suboptimal historical management and the inadvertent redistribution of contaminated soil during historical earthworks. By demonstrating that the plant had been present in over 40 locations for more than 25 years, the investigation provided the technical evidence needed to address complex claims of contractor negligence and liquidated damages, successfully shifting liability back to the site’s long-term historical mismanagement.