A Practical Model of the Natural Attenuation of Oil on Shorelines for Decision Support

Oil stranded on shorelines naturally weathers and attenuates at rates that are a function of the character of the oil on the shoreline (type and volume), the character of the shoreline materials, and the environmental setting (physical and biological). Some light crude oils and refined products have a very short half-life and may persist for only hours or days. However, if stranded oil is not exposed to light, oxygen or physical shore-zone processes, such as in asphalt pavements or if buried by marine or river sediments, it may take long time periods to fully degrade, or in a few extreme cases may not degrade at all. This review assesses the current state-of-knowledge of the natural weathering and attenuation of oil on shorelines as this relates to decisions regarding a shoreline treatment program. This knowledge is critical for the creation of simulation models for natural attenuation. The Shoreline Response Program-Decision Support Tool, currently under development, considers the various translocation (transport) pathways of oil on shorelines into the atmosphere or the marine environment and the attenuation processes that lead to the final transformation of stranded petroleum hydrocarbons into non-hydrocarbon materials. This ultimate transformation to a non-hydrocarbon is only achieved during chemical attenuation processes associated with biodegradation or photodegradation acting on exposed oil surfaces. Understanding the processes that act on the stranded oil and the rates by which oil is transformed into non-hydrocarbon materials is crucial in the decision process on whether to let Nature take its course or to intervene to remove the oil and/or accelerate the weathering and attenuation processes. This review evaluates the current state-of-understanding regarding the initial behavior and ultimate fate of oil on shorelines, identifies knowledge gaps regarding the behavior and ultimate fate of oil on shorelines, and recommends topics for further investigation and future research.