Newcastle Port Sediment Toxicity Investigations to Identify Sediment Suitable for Unconfined Sea Disposal

Dredging of some 13.5 million cubic metres of material from the South Arm of the Hunter River at Newcastle in NSW is proposed as part of major port expansion works. The scope of dredging includes removal of soft silty clays, estuarine sands, stiff clay and rock. The silty clays are generally contaminated with heavy metals, polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs). The highest concentration of contaminants is located in an area immediately adjacent to the former Steelworks Site. It is proposed to dispose of the soft silty clays at sea or, where contamination levels prohibit unconfined sea disposal, to remediate the material and dispose of it on land. Sediment proposed for unconfined sea disposal must be assessed in accordance with the National Ocean Disposal Guidelines for Dredged Material (Department of Environment and Heritage, 2002). The mean concentration of several contaminants within the soft silty clay layer triggered the need for sediment toxicity testing in accordance with these guidelines to determine its suitability for unconfined sea disposal. A series of sediment toxicity investigations was undertaken by CSIRO Centre for Environmental Contaminants Research to identify the toxicity causing contaminants in the silty clays and to determine the level of contaminants that could be tolerated by aquatic organisms, thereby deeming the sediments suitable for unconfined sea disposal. The main findings of the CSIRO investigations together with advice provided by key State and Commonwealth agencies was then used to determine the sediment that is suitable for unconfined sea disposal from the sediment that must be remediated on land. Significant refinement of the volume of sediment considered unsuitable for unconfined sea disposal was achieved through the series of sediment toxicity investigations and the consultation process.