Mosjøen Harbour remediation works achieve CEEQUAL rating of Excellent

Alcoa Mosjøen Harbour is located in Mosjøen, Vefsn county in Norway and is the harbour area for Alcoa Mosjøen. It’s in the inner part of Vefsn Fjord close to the outlet of the river Vefsna. Since 1958, it has produced aluminum in Mosjøen and this has led to heavy contamination of the sediment, mainly consisting of PAH. Today’s production technology is not leading to any further contamination of the basin.

Mosjøen Harbour remediation includes dredging contaminated sediment and placing of this sediment in steel sheetpile cells (CDF) to create extension to an existing wharf. After the dredging was completed the seafloor was capped with clean materials including sand and gravel.

During dredging, the turbidity and movement of sediments was closely monitored both close to the barges and in carefully selected places in the fjords.

Main activities during construction:

• Measuring the sea floor before and after dredging
• Clean up of the sea floor before dredging
• Protection of the sea water intake prior to works, which us is crucial to the production in the smelter as it is used for purification of gasses from the electrolysis
• Improvements of existing wharf
• Construction of 6 CDFs
• Dredging 30,000 cubic metres of sediment
• Water treatment of the water from the cells
• Capping of the sea floor after dredging
• Stabilisation of the dredged material after placement in CDF
• Placement of cover – CDF is now an extension of the existing wharf
• Monitoring before, during and after dredging and capping, as well as mitigation actions:
• Current measures, turbidity, sediment trap – the results were used for the total calculation of environmental budget
• Noise and dust mitigation.

The challenges posed to this project included:

• The high level of ship traffic in the harbour
• The need to avoid interrupting operations both in the harbour and nearby industry
• Protecting the stability of the wharf during sediment remediation operations
• Maintaining operation of scrubber water intake during operations
• The need to limit movement of sediments outside the harbour during the dredging.

This project had particular success in project management and in the water environment.

Project management
Since the main purpose of this project was to improve the situation regarding polluted sediments in the harbour, the goals for the results were very clear from the beginning and the whole project team worked with this in mind.

All works and activities were recorded and followed closely to be sure the goals were reached. The sustainability aspects were integrated in the overall process for the project.

Water environment
The quality of the water both in the Vefsnfjord and in the river Vefsna were monitored and followed closely during the dredging and after completion of the project. It was necessary to have good control of the distribution of the sediments during the operation and prevent it from polluting the recipients close to the harbour. Turbidity measures at selected stations were done continuously and target values set for spreading. Salinity, temperature and current were measured. Also, stations with mussels are being monitored.

Water from CDF (after disposing the sediments) had to be treated not to spread pollutants back in the harbour and the Vefsnfjord. This was done by designing a water treatment plant meeting the requirements of maximum 60 mg SS/L water.

The environmental budget and calculations done after completion of the project shows that more than 15,000 kg PAH have been removed from the harbor.

The constructor, NCC, thought it was of great interest to test the CEEQUAL methodology to see how the project and processes complied with the certification. Alcoa Mosjøen was a suitable project at the time with clear environmental and social goals for the outcome of the project. CEEQUAL was initialised by NCC after the project had started.

Best practice and innovation
Placing the dredged contaminated sediments and material in the CDF and not transporting them to a landfill was a very good choice from many perspectives. It meant that transportation of the material over land was unnecessary. Also, the construction of the CDF was a part of an extension of the existing wharf which improved the capacity of the wharf with 250m waterfront.

The use of local material as gravel and sand for capping significantly reduced the need for transport, compared to if the material had been taken from another source.

Value for money
Implementing the CEEQUAL methodology showed that NCC’s processes and way of working comply with the demands of CEEQUAL. Furthermore, some area for improvement in the environmental management system was identified. For NCC this process has been very useful even though it has not been easy to calculate the benefits in an exact amount of money.