Stabilization of Dredged Sediments: Enabling Beneficial Re-Use Solutions in a Contaminated Port

Before 2017, Port Nelson’s Calwell Slipway was ranked the second most contaminated site in New Zealand, due to toxic materials that were historically used in boat antifouling. Maintaining the slipway’s navigability was fundamental to the port’s continued operation given the basin had not been dredged since 1984, but the sediment was too contaminated with copper, tributyltin, and other contaminants to dredge and dispose of offshore or upland. The port had to find an alternative. The solution comprised dredging the contaminated sediments and stabilising with a blend of ordinary Portland cement and activated carbon. Extensive laboratory testing and field trials were undertaken to determine optimum blend. This material was then used to reclaim additional land for the port. The stabilisation and beneficial reuse of contaminated sediments is a viable strategy for remediation of marine sediments where traditional disposal methods are not available, even in a developed port within a small footprint.