Deep water disposal site, Oslo Harbour

NGI's role in the project "Clean Oslo fjord" is to ensure that the deposition of contaminated sediments from Oslo Harbour to the deep water waste disposal site at Malmøykalven fulfills the concession requirements established by the Norwegian Pollution Control Authority (SFT).

The contamination of sediments in the Oslo harbour is mainly accumulated on the sea bed at shallow waters. This implies that small boats and large ship traffic is swirling up the contaminated sediments which subsequently are spread by the water currents and thereby may affect the food chain. The monitoring shows that spreading of contaminated sediments is very limited and is well below the accepted limits.

The clean-up
The contaminated sediments that will be treated have a varying thickness, from a few centimetres to two meters. In shallow waters, the contaminated sediments are removed by dredging and deposited at the deepwater site Malmøykalven at 70 m water depth.

In less shallow waters of the inner Oslo fjord, the contaminated sediments will be covered by clean soil masses, in order to minimize the swirling up and spreading of contaminated sediments by the boat traffic. During dredging period the swirling up of contaminated sediments will increase. After the end of the project period the spreading of contamination will of course be drastically lower than prior to the clean-up period. This is included in the environmental budget for the project.

The contaminated sediments in Oslo Harbour are not classified as special category waste, which has a much higher concentration of poisonous substances. The total mass volume in the Oslofjord project that will be dredged and deposited is about 600,000 m3. This volume corresponds to about two times the volume of Ullevaal Stadium (which has a capacity of about 25,000 spectators) filled up to the uppermost tribune. It is not practically possible to separate the different poisonous substances from such huge volumes of contaminated soil. A careful and controlled disposal of these sediments is therefore the most appropriate solution.

Monitoring
Depending on the substances under consideration, the observed spreading during dredging and deposition to the deep water site corresponds to the amount found in 10 to 40 m3 dredged sediments. For PCB the results corresponds to that 17 grams have leaked out from the deep water waste disposal site at Malmøykalven by the summer of 2007. This amounts to only 8% of the total amount that has been the basis of the dredging permission.

For comparison the small rivers Akerselva, Alna and Loelva feed between 40 and 150 grams PCB per year, while the Bekkelaget Cleaning Facility is producing between 50 and 70 grams PCB per year.

In other words, the monitoring of the contaminated sediments shows that the spreading implied by the environmental budget of the project, is very low compared to other contaminating sources. There will be no notice of spreading of contaminated sediment particles or mud to the recreational areas around the Oslofjord.

To conclude, the work in connection with the clean-up of the Oslofjord is governed by, and abide with good margin, the strict regulations of the Norwegian Pollution Control Authority (SFT).