Updated remediation action plan for contaminated sediments outside Elkem Carbon, Kristiansand.

Summary

This report is an update to NIVA report 7276-2018 " Tiltaksplan for forurenset sjøbunn utenfor Elkem Carbon, Kristiansand " (Olsen and medarb. 2018). Based on new analyses and modelling, the design of erosion protection has been presented as part of capping layers of the contaminated sediments in Elkembukta. The erosion protection will prevent resuspension from ship maneuvering. The capping layer and the erosion protection layer must be designed in accordance with applicable regulations and standards. In this context, geotechnical calculations should also be carried out to control stability and carrying capacity in the area. In Fiskåbukta, where the risk from PAH is relatively small and the condition of sediment-living animals is good, it is in the remediation action plan recommended monitored natural recovery to monitor the effect of emission reductions on sediment concentrations and ecological risk associated with PAH. The recommendation does not change as a result of this update. In recent years, Elkem Carbon has focused on source control to reduce emissions. This has meant that inflows to sea of PAH with process water today are in the range of 5-10 PAH16 per year. Elkem Carbon is in the process of reducing PAH with surface water. As of today, estimated discharges of surface water are in the range of 25 kg of PAH16 per year. Further measures are being taken to reduce this. This work is important for minimizing the recontamination of the capping layers and it is recommended that this work be given priority.