In-situ Capping of Contaminated Soft Seabed Sediments in a Norwegian Fjord

Naturally available glacial deposits of sandy silt and sand materials have proven to be a safe and feasible geo-environmental solution for isolating heavily polluted soft marine sediments in the inner basin of Kristiansand fjord in southern Norway. A major industrial plant for refining nickel, copper and cobalt, is located in the area, and causing most of the pollution. The surrounding marine sediments are seriously polluted and affect the fauna in the fjord. Furthermore, restrictions were imposed by the authorities, on consumption of the sea food from the area. This paper describes findings from tests and studies performed as part of the design of the capping structure. It also describes the placement procedures developed for remediation construction work. Some results of the control monitoring programme during the subsequent years, with respect to geotechnical stability and effects on the marine fauna, are also presented in view of defined remediation performance criteria.