Ichthys Gas Field Development - Oceanographic Discharge Modelling Study.

The oceanographic discharge modelling study will provide a quantification of the likely trajectories, fates and consequences of the following production discharges and potential accidental spills that have been identified to date: - Produced formation water; - Grey water and sewage; - Hydrotest water from dewatering of the export pipeline; - Wastewater from a desalination plant; - Sediment suspended by dredging/trenching for the subsea pipeline, including potential discharge from directional drilling from land; - Disposal of the dredge-spoil; - Sediments suspended by propeller-wash from export tankers - Sediments suspended during construction activities; and - Accidental releases of liquid hydrocarbons into the sea. These studies examine realistic scenarios based on the planned activities and account for trends and variations in ambient conditions. Modelling studies will require the development of fit-for-purpose hydrodynamic models to suit the various studies. Some studies will require modelling that covers a relatively large area and incorporates hourly to decadal time-scales. Others will require modelling at finer spatial and temporal scales. Objectives: The objectives of the Oceanographic Discharge Modelling Study are to: - Predict the hydrodynamic circulation over the wider study area and local Islands using a validated three-dimensional hydrodynamic model; - Predict the exposure risk from accidental hydrocarbon releases (trajectory, dispersion and weathering of hydrocarbons spills) using a validated dimensional oil spill fates and effects model; - Predict potential deposition and erosion of sediment in sensitive areas such as beaches and benthic primary producer habitats through coastal transport modelling; - Predict the fate of sediments released from dredging, dredge spoil disposal and propeller-wash using a validated 3-dimensional spill fates and effects model; and - Provide model output data to support the assessment of potential impacts arising from accidental hydrocarbon spills associated with the Inpex project. These include the provision of: Time-series plots showing the predicted weathering of the specified oil types under local conditions; Contour plots showing probability of exposure to shorelines and open water locations; Contour plots showing the minimum elapsed time before exposure by slicks at locations; Contour plots showing the average and maximum concentration of surface oil at locations; Probability of exposure to entrained oil at sub-surface locations; Potential concentrations of entrained oil at sub-surface locations (maximum and average); Probability of exposure to dissolved aromatic (BTEX and PAH) hydrocarbons; Potential concentrations of dissolved aromatic hydrocarbons in the water column (maximum and average); and Maximum cumulative doses (concentration x time of exposure) of dissolved and entrained components at sub-surface locations.