| Summary: | The appearance of on-bottom oil following surface and deep water spills has been well documented. A very likely, yet sparingly studied, cause of this phenomenon is the evaporation and/or dissolution of the light constituents of the mixture, leaving a heavy residual fraction that may sink. A binary mixture of a light, volatile/soluble and a heavy, nonvolatile/insoluble component was used in numerous laboratory experiments, with binary and multi-component mixtures, to confirm this event is possible. A binary-component model was developed based on the law of conservation of mass for oil spilled on the surface to predict sinking time requirements based on the physical properties of the mixture and environmental conditions of the spill. The EVAPO-SINK model predicts the necessary time required to produce oil of a density greater than water which results in its sinking. Evaporation is the dominant weathering event and is featured in this model. The SOLUTE-SINK model was developed for oil spilled at depth in the water column and predicts the necessary time for it to achieve negative buoyancy due to weathering by dissolution. The binary theoretical model was extended to multi-component mixtures by the creation of two pseudo-components, one for the combined light chemicals and another for the combined heavies, and tertiary and quaternary mixtures were tested. The pseudo-component model was compared to an exact multicomponent model and experimental results. This research is a proof-of-concept, a necessary first step in the determination of if and when a hydrocarbon mixture, located on the surface or suspended in a fresh or salt water column, will sink.
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