Contaminated Sediment Management by Capping and Deep Water Confined Aquatic Disposal in the Harbor of Oslo

Dredging has been prohibited in the harbor of Oslo in the past 15 years as a result of serious sediment contamination. Through a joint effort of the Oslo Harbor Authorities, the Norwegian Road Administration, and the Norwegian Pollution Control Authorities, a remediation plan for the redevelopment of the old harbor of Oslo has been implemented. The plan, which will be completed in 2009, includes dredging of the shallow parts of the harbor down to 15 m of water depth (approximately 450,000 m3), capping of the deeper parts of the harbor (1,000,000 m2), as well as construction of a deep water confined aquatic disposal facility for the dredged material at 70-m depth in the inner Oslofjord. To prevent uncontrolled contaminant transport, an on-line monitoring system is operated that consists of buoys with turbidity loggers and a water current velocity meter. Passive samplers are used for time-integrated sampling of organic contaminants. In addition, periodic sampling and analysis of water and suspended solid samples are carried out. To document the environmental benefit from the remediation, contaminant transport is quantified before, during, and after remediation using flux measurements based on in situ diffusion chambers. Monitoring results show that remobilization of contaminants has been very limited and do not exceed the amounts defined in the environmental permit from the pollution control authorities (environmental budget). Capping resulted in more than 90 % reduction in contaminant flux.