“The volume of knotweed was calculated and the cell size determined in accordance with that,” added Wyn. “The site was also tested to ensure the cell’s creation would not increase the risk of flooding in the locality.”
Wyn explained that the cell was shaped and lined with a root barrier membrane specifically designed for the burial of Japanese Knotweed. A base is formed and welded together. Once the base liner is in place, excavation of knotweed-infested soil can begin. It was hauled in dumper trucks and buried in the cell. The material was placed in layers and tracked in place. Once it had all been removed, under the guidance of site ecologist Mike Head, the containment cell was sealed and capped.
“This is a tried and tested method which is safe to the environment and has no long-term effects on the surrounding area,” added Wyn
Site ecologist Mike Head has also been dealing with the discovery of a lesser horseshoe bat maternity roost found close to the bypass scheme at Minffordd. Measures to mitigate the loss of this environmentally sensitive bat habitat include the purchase of land next to the scheme to create a new habitat.
“This has involved transforming an old landfill of minimal nature conservation value into a bat foraging habitat,” he said. “It has included the creation of new hedgelines, mounds and deadwood habitats. Species-rich grassland has been translocated to the site and wildflower seed has been spread across it. The new site also offers valuable habitat for reptiles, invertebrates and badgers.”
At the same time archaeologists unearthed evidence of Roman-era occupation along part of the route. Gwynedd Archaeological Trust discovered evidence of a stone kiln and pieces of roofing tiles dating back centuries.
Archaeologists identified three distinctive areas of activity including a deposit of roofing slate, a former stone-built kiln and patches of burning. The team chose to investigate the site further after earlier archaeological work a short distance away resulted in the discovery of a former Roman bathhouse. A visitors’ centre has been set up in Porthmadog to enable people to view the archaeological finds as well as details of environmental conservation work and information about the construction project.
Visitors to the centre can also watch an informative video presentation running on a loop, as well as a Powerpoint presentation about the archaeological work.
At its peak, some 250 construction workers will be on site during the project.
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