Silverton Mill, Exeter – Remediation

Client : D S Smith
Programme : 3 years
Value : £4.5m

As Principal Contractor John F Hunt was contracted to demolish and remediate a former paper mill that straddled a major river (River Culm) in Devon. The mill had a heavy industrial usage dating back to the 1800’s and left a significant pollution legacy in the form of heavy and light hydrocarbons and asbestos in the soils.

The initial design problem, was how to remediate the contaminated ground either side and beneath an existing culvert, which had a substantially active water flow and a very rapid flood response during heavy rainfall.

Remediation works would need the ground either side of the culvert to be excavated and treated whilst the river was flowing and there was a serious risk of contamination to the river.

The John F Hunt team designed, agreed and constructed a river diversion (pictured right) so that the flow through the culvert could be stopped, allowing remediation of the ground around it and the eventual restoration of a naturalised river channel.

The excavated and treated materials were subjected to a strict stockpile and materials management process. This allowed testing, categorisation and segregation to be undertaken without mixing wastes and materials, therefore enabling suitability for re-use. The work was carried out under a CL:AIRE code of practice Materials Management Plan.

  • Demolition of the above ground structures to ground level and then excavation and removal of below ground structures.
  • Design and construction of the river diversion channel including regulatory negotiation and agreement of the design.
  • Full Principal contractor role with management of all aspects of the works.
  • Dynamic process of investigation and material categorisation during the excavation process to respond to site investigation data gaps.
  • Use of a CL:AIRE code of practice materials management plan to regulate the sorting and re-use of materials at the site.
  • Excavation, pre-treatment and disposal of waste construction materials, soils and sediments.
  • Active stakeholder engagement including client, regulators, third parties and the freeholder.
  • Construction of a groundwater base flow alleviation system, using site won materials, to prevent erosion of the new south river bank.
  • Construction of the new river channel post remediation including and groundwater base flow alleviation system, rock armour flow protection and restoration of grassed embankments.

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