Remediation of contaminated sediments in Oslo Harbour,Norway

During the past 60–70 years, contaminated sediments from local rivers have been settling in the harbour basin of Oslo. This contamination, combined with that from other harbour activities, has developed into a serious pollution problem with both organic and inorganic contaminants. Since 1992 dredging activities have been restricted until the effect of dredging was determined and a safe disposal was found for the sediments. Because of this restriction, a conflict situation arose in terms of decreasing sailing depths, and dispersal of large quantities of contaminated sediments into the water column each day from ship traffic. A complete plan of action to remediate Oslo Harbour was started in 1994 and delivered to the State Pollution Control Authority (SF1) in August 1996. An evaluation of environmental risks connected to the remediation work has been carried out along with the determination of the requirements for the monitoring programme during and after the work. Preliminary evaluation of dredging techniques indicates that mechanic/hydraulic equipment will cause the least dispersion of sediment. Several options for treatment of the sediments have been evaluated. Study results point out that conditioning prior to disposal of the sediments in a confined disposal site in the harbour area, is the most cost effective solution. Seven disposal sites with a capacity of 0.5 mill. m³ have been identified. Two of the sites are integrated with a subsea road tunnel crossing the harbour basin. The other disposal sites will serve as new dock area after closure.