Case Studies: Treatment & Disposal of Contaminated Dredgings

The Problem

• Contaminated dredgings from a busy fishing harbour had to be disposed of, following the withdrawal of the licence to dispose of these to sea.
• Contamination consisted mainly of anti-fouling agents Tri-butyl-tin (TBT’s) and hydrocarbons.
• Total volume of dredging was approximately 11,000 m3.
• Landfill disposal of the dredgings as they arose from the dredging process was very expensive.

The Solution

• A waste management licence for a treatment facility was obtained from the regulators for the project duration and a water discharge licence granted.
• A specially designed storage lagoon was constructed for the dredged material, with a sump in one corner to collect the liquid run-off.
• This liquid run-off was treated by pumping through a series of filters and separators to reduce contaminant concentrations to acceptable levels before being discharged under licence to the sewer.
• The dredgings were treated on site by a process know as stabilisation, where cement is added to the material and thoroughly mixed using a specially adapted mixing unit.
• The stabilised materials were then transported to a landfill to be used as landfill cover.

The Benefits

• The client was able to maintain the use of the busy fishing harbour during works and comply with new legislation regarding the disposal of dredgings using an economic solution.
• By a process of treatment an engineered material was produced, which rather than being landfilled was used to provide much needed landfill cover for the landfill operator.