Japanese Knotweed – Development of Retail Superstore


Japanese Knotweed was identified at a client’s site where previous site activities, including levelling had caused the spread of the rhizomes across the site.

After conducting a survey of the spread of the Japanese Knotweed, several remedial design solutions were developed and proposed to the client.

The remedial design options as part of the development of a new £10 million Retail Store were as follows:

  • The collection of rhizomes and plant stems and processing of material by a specialist contractor to enable the re-use of the material on site;
  • The collection of rhizomes and plant stems and placement of material at depth (>5m) within an excavation;
  • The collection of rhizomes and plant stems and placement within an area on site, followed by treatment by herbicides over a period of three calendar years;
  • The excavation of material to a depth of approximately 3m below ground level and the treatment of material at the site boundary by application of herbicide for a period of three calendar years.

A cost plan was developed by REC which detailed the alternative strategies for the development of the site. In the end it was decided to remove all impacted materials in accordance with a remedial method statement developed by REC and sent to the regulators. A landfill tax exemption was also applied for and received from the Inland Revenue, saving the client over £100,000.

REC assisted in the development of the tender documentation for the programme of remediation and also provided the independent validation of the removal of the Japanese Knotweed. Upon completion of the removal of the plant a Validation Completion Report was dispatched to the Local Authority and the site declared suitable for use.