Residual Contamination at Seabed due to Vertical Transport of Oil Nadim Copty 1 , Emre N. Otay 2 and Paul A. Work 3 1 Institute of Environmental Sciences, Boğaziçi University, Istanbul, Turkey 2 Civil Engineering Department, Boğaziçi University, Istanbul, Turkey 3 Civil Engineering Department, Clemson University, Clemson, SC, USA Abstract A one-dimensional, numerical model describing the fate and vertical transport of oil spilled on the surface of a water body is presented. The model simulates the movement of oil through a control volume that extends the full thickness of the water column. The model includes the processes of emulsification, dissolution, and biodegradation of the oil in the water column. Vertical forces (weight, buoyancy, and drag) on an individual oil droplet are also included. The time-dependent release of oil droplets from the sea surface into the water column, controlled by the energy dissipated at the sea surface by waves and other parameters, is modeled stochastically. Droplets may change density and/or size due to emulsification, dissolution, and biodegradation once introduced to the water column. Collision with suspended solids may cause droplets to fall to the seafloor, this motion being resisted by the buoyant and drag forces. The model provides a description of the fraction of oil present in each phase or region of the model: on the surface, at the seafloor, or dissolved, suspended or biodegraded in the water column. A hypothetical case study is presented illustrating application of the model and the influence of the application of a chemical dispersant. This example shows that the fraction of oil reaching the seafloor may increase significantly when chemical dispersants are used. The findings of this study can be refined provided site data are available to better describe the processes affecting the modeled oil droplets. Extension to two- or three-dimensions is also feasible, introducing the processes of advection and dispersion. 1 Introduction Following an oil spill in the open sea, properties of the spilled oil and conditions at the sea surface determine the fate of the oil. Most oil spill accidents are accompanied by high winds and rough sea conditions where oil particles undergo complex physical and chemical processes at the sea surface. The dominant processes are evaporation, emulsification, dispersion, spreading, dissolution, oxidation, biodegradation and sedimentation (Figure 1).