Principal Contractor for Japanese Knotweed Removal

Principal Contractor for Japanese Knotweed Removal

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Principal contractor

In this case study we review Japanese Knotweed Ltd working for a large UK housebuilder to remediate Japanese knotweed and other Invasive weeds on a development site in southern England

Initial Investigation and Site Preparation Works

Restricted Access due to Vegetation

During initial pre-work investigations the site was not easily accessible due to overgrown brambles and other dense native vegetation. We would usually cut access paths into the site to identify all areas of Japanese knotweed (JKW), but we were unable to do so due to the presence of protected reptiles. Without creating access paths, we were able to identify four stands of JKW to the area.

Working Alongside Ecologists and Demolition Contractors

For the site clearance and preparation work phases the Demolition contractor acted as principal contractor, with Japanese Knotweed Ltd (JKL) providing watching brief and bio-security control services.

Ecology works

We returned to the site six months after the initial investigation visit, to work alongside an Ecologist to access and inspect the site.

We provided an invasive weed Watching Brief, whilst the Ecologist searched for hibernating reptiles. To enable this, they cut down vegetation, which allowed us further access into overgrown areas of the site.

With the clearance of the vegetation, we identified additional areas of JKW (fourteen areas in total), some of which were new growth.

Japanese knotweed site plan
Site plan showing areas of JKW

Demolition works:

The site possessed an old barn scheduled for demolition.

We provided temporary materials to demark, cover and protect knotweed contaminated ground. Reducing the risk of accidental disturbance and spreading of knotweed during demolition works.

Under our Watching Brief, a cesspit (discovered by the Ecologist in clearing site vegetation) was pumped out and the concrete chamber removed, the barn was demolished to ground level, and foundations broken up.

Our supervision enabled JKW contaminated material to be separated from clean to reduce project costs and ensure legal waste reuse and disposal.

Working on site
An old barn was marked scheduled for demolition

Discovery of Unmarked Underground Services

During our supervision of the demolition contractor, they found services that were not marked on the service drawings.

JKL and the Ecologist provided a Watching Brief whilst the demolition contractor carried out trial hole digs to identify the exact location and depths of the services.

The newly discovered services were active, and within an area at risk from containing Japanese knotweed rhizome.

These areas had to be hand dug to fully expose the services and to enable inspection for the removal of the Japanese knotweed in this area.

Unmarked underground services
Unmarked underground services

Following the site clearance works, we took over as Principal Contractor, to continue site works in accordance with CDM regulations 2015. Works were conducted during the covid-19 pandemic requiring specific RAMS and additional Toolbox talks for all contractors attending site.

Our Role as Principal Contractor

As Principal Contractor, we were responsible for the coordination and Health & Safety of all workers on site, including site welfare facilities and signing in and out procedures. We provided a First Aid muster station where there was an air horn that could be sounded if there was a site emergency. We were responsible for erecting and maintaining correct contractor and public safety awareness site signage and ensuring the correct use of PPE by personal on-site all-in compliance with CDM 2015 Regs.

The works were completed during the COVID-19 pandemic. Our Toolbox talk included COVID-19 Government compliance and procedures. We additionally had a COVID-19 specific RAMS that was delivered during the Toolbox talk and signed and agreed to by all contractors and visitors.

Managing Hibernating Protected Reptiles

Due to the previously assessed presence of hibernating reptiles, we were unable to freely move our plant and equipment across the site.

To enable access and additionally Archaeological site works, all access routes to the JKW areas and Archaeologist work areas had to be scraped whilst under the Watching Brief of the Ecologists to check for reptile presence.

JKL carried out various excavation works for the Archaeologists, creating several exploratory trenches around the site.

Managing hibernating reptiles
Managing hibernating protected reptiles

Japanese Knotweed Removal

While acting as Principal Contractor we undertook the excavation and removal of Japanese knotweed from the development site to allow free unimpeded works to develop the site on completion.

Most Japanese knotweed locations were carefully and fully excavated to remove all knotweed rhizome while being diligent in only removing ground contaminated with rhizome thus reducing the overall waste volumes and project costs. The knotweed contaminated waste once removed from site was classed as controlled waste and removed via registered waste carriers to a specifically licensed landfill facility for disposal. In total, we removed over 720 tonnes of knotweed waste to landfill.

JKL is also responsible for the long-term herbicide treatment and control of other invasive plants on site. These are located outside the development works footprint in locations classed as Site of Special Scientific Interest (SSSI)..

Root Barrier Installation to Prevent JKW Ingress

A soakaway pipe that was not detailed on the site drawings was discovered by JKL. It travelled through the centre of excavation works for removal of knotweed stand JK6.

We carefully excavated to either side of the pipe to fully expose it. As the pipe flowed uphill, with the agreement of the client, we removed the pipe at a T-section and capped it with a stop end.

JK6 was surrounded by an L-shape retaining wall at the site boundary. Unfortunately, the rhizomes had travelled underneath the footings of the retaining wall.

We increased the excavation depth beyond the level of lateral rhizome travel under the footings and installed a vertical root barrier to the boundary wall to help prevent future ingress of JKW into the site.

Root Barrier Installation
Root barrier installation

Working Under Arborist Watching Brief

Some knotweed locations were located within tree root protection zones.

For our plant/equipment to access within the tree root zones, we laid out protective boards to spread the weight of the machine and thus reduce ground compaction.

The areas were mechanically scraped and excavated under Watching Brief of Arboricultural Consultant.

The excavation was conducted by scraping ground layers off an inch at a time. If we had come across any tree roots, we would have had to resort to hand digging the knotweed.

We completed a reduced level dig with root barrier capping in these locations in accordance with a works method for this area of the site.

Root barrier capping
Root barrier capping

Excavation of JKW Under Driveway

In another area of the site, we discovered JKW rhizomes extended under a tarmacadam lane that serviced nearby offsite properties. The rhizomes had infiltrated a land drain and were growing within and along the drain. Our client installed a temporary diversion to the lane, thereby maintaining access to the properties. With the diversion in place, we were able to fully excavate the area and remove the knotweed rhizomes.

Come Rain or Shine: Inclement Weather

During the works, there was torrential rain, making excavating and moving equipment and contaminated soil around the site much more challenging.

Inclement weather
Inclement weather

Other Invasive Non-Native Weeds Control

In addition to JKW, there was also Rhododendron ponticum (RP) and Himalayan balsam (HB) on-site, both of which are listed as invasive species within the Wildlife & Countryside Act 1981, Section 14, Schedule 9, part 2.

We cut down the RP, opening up the densely vegetated area. The cut stumps of the RP were treated by drilling and installing Ecoplugs to provide slow-release herbicide delivery into the plants.

The HB was growing within an SSSI area and the use of herbicide for control was not permitted. Therefore, we hand-pulled the HB before the plant could flower and produce seeds, thus controlling and preventing its spread. Both the RP and HB works are long term with JKL conducting repeat monitoring and treatments for several years to gain control of the invasive plants.

Contact the Knotweed Experts

Japanese Knotweed Ltd is the UK’s trusted company for providing surveys, treatment and removal services for Japanese knotweed and other invasive weeds.

We are a private limited company, working throughout England, Wales, and Scotland for all types of customers, including construction, developers, facilities management, housing associations, local authorities, property maintenance and private property owners.

Japanese Knotweed Ltd is a ‘safety first’ contractor, holding a range of safety SSIP and industry-related accreditations. These accreditations are supported by our commitment to provide the highest level of employee training, expertise, and customer service standards in the industry.

The company employs staff across the UK to provide an efficient and responsive service. It enables us to deliver over 150 excavations and 8,000 herbicide visits per year for more than 6,000 customers. Our services cater for project values in the range of £500 up to £1.5M. Recent works include completing two excavation contracts simultaneously over a period of 2.5months with a combined value of £1.8M. The annual turnover for 2020 was £4.6M.

As well as dealing with Japanese knotweed, we also control all other non-native invasive weeds such as Giant hogweed and Himalayan balsam, as well as native common weeds such as Horsetail. We provide work programmes that include excavation for immediate removal, or herbicide treatments for longer-term control. Our methods are tailored to each site to provide a sensible and efficient solution to meet all requirements.

Japanese Knotweed Ltd is a member of the Property Care Association, with CSJK qualified surveyors and Insurance Backed Guarantees provided for Japanese knotweed work.

In relation to our excavation works, we employ skilled and qualified staff including CSCS (100%), CPCS and SSST, with associated training such as asbestos awareness etc. For herbicide works, we employ a BASIS advisor, and our staff possess the statutory NPTC PA1/PA6 tickets, plus we are affiliated to the Amenity Standard and members of the Amenity Forum.