Institution: Florida International University
Proposal No: 1043467
Response to oil spills at sea involve containment of the floating oil (slick) with booms and surface removal. Initially the major fraction of the oil floats, hence, this method can be affective for containing small spills. Over time, waves and tidal action result in dispersion and emulsification of the oil slick (i.e., formation of stable small droplets). Emulsified oils can remain within the water column for extended periods of time and can move with the underwater currents. There are significant knowledge gaps relative to emulsification rates and patterns of large oils spills at sea (i.e., effects of weather conditions, waves, tides); partitioning profile of oil between slick and emulsion phases over time; persistence and mobility of dispersed oil droplets in water column; and transport characteristics of emulsified oils in relation to surface slick. Immediate short term research effort will focus on integrated analysis of data from satellite images of surface slick size and patterns, weather conditions (i.e., wind, temperature), and marine conditions (wave height from NOAA Bouy data). The data sets will be coupled with data from water samples collected at various locations over time to characterize persistence and mobility of emulsions.
The research objectives are: (1) Investigate emulsification rates and patterns of large oils spills at sea (immediate short term); (2) Characterize persistence profile and mobility of emulsified oil at sea (short and long term); (3) Determine critical emulsion formation and transport characteristics based on field observations in South Florida marine and coastal waters and data in the Gulf coastal areas and marine environment. The research plan consists of the following tasks: (1) Coordination and communication with agencies and researchers to exchange data and information; (2) Field data analysis in the Gulf; (3) Field data and assessment in South Florida coastal and marine environment; (4) Analysis of data to determine critical emulsion behavior parameters; and (5) Macro scale assessment of emulsion behavior and persistence characteristics in subtropical environment.
Broader impacts of the research will include dissemination of findings through the American Society of Civil Engineers (ASCE) Council of Disaster Risk Management (CDRM) Outreach Committee efforts thorough development of informative modules on oil spill risks and emulsion formation, development of a course module on emulsion behavior, and journal papers.
Response to oil spills at sea involve containment of the floating oil (slick) with booms and surface removal. Initially the major fraction of the oil floats, hence, this method can be affective for containing small spills. Over time, waves and tidal action result in dispersion and emulsification of the oil slick (i.e., formation of stable small droplets). Emulsified oils can remain within the water column for extended periods of time and can move with the underwater currents. There are significant knowledge gaps relative to emulsification rates and patterns of large oils spills at sea (i.e., effects of weather conditions, waves, tides); partitioning profile of oil between slick and emulsion phases over time; persistence and mobility of dispersed oil droplets in water column; and transport characteristics of emulsified oils in relation to surface slick. Research activities focused on integrated analysis of oil behavior, surface slick size and patterns, effect of sea conditions (wave height). Numerical analyses were conducted with field data available from various sources to determine: 1. Emulsification rates in relation to location specific parameters; 2. Mobility of emulsion phase relative to slick location; 3. Persistence of the emulsified oil in water column; and 4. Partitioning dynamics of oil between slick and emulsion phases with time. The project activities were integrated a course which is cross-listed for undergraduate and graduate students. The students worked on different aspects of oil spills in deep sea and shallow waters, effect of temperature on decomposition and transformation rates of oil fractions, and effect of solar radiation and sea conditions on breaking of the oils slicks. Major research findings include the following: • Transformation and partitioning of oil between air, water, and sediment phases result into different transport and persistence patterns. Transformation and partitioning behavior (i.e., rates and patterns) of oil in different phases (i.e., slick, dispersed/emulsion phase, adsorbed fractions) over time define persistence profile of petroleum hydrocarbons (PHCs) in natural systems. • During breaking of the waves and collapsing on the oil slick, as a result of the dissipation of the shear energy, oil droplets are detached and entrained into the water phase. Depending the intensity of mixing and characteristics of water and droplets; the oil droplets can remain detached, resurface, and/or coalesce with the main oil slick; or resurface and form separate slick trailing the main slick. • From a spill management perspective, emulsification at sea adversely affects the spill management efforts since emulsified oils are more viscous than the original oils and droplets can move faster than the slick phase. • Emulsification rate is proportional to the energy dissipation from the waves into the mixing layer which depends on the sea conditions. • In the mixing layer the efficiency of air stripping depends on a combination of wave height, depth and temperature, although no single variable dominates the efficiency. In addition the solubility of the compound effect how quickly it can be removed by stripping in the mixing layer. • The concentration of PAH in the water can exceed their solubility by emulsification of oil (i.e., presence of oil droplets in water column). Due to high sediment-water partition coefficients of the PAHs, the sediments can accumulate relatively high levels of PAHs • Persistence profiles (as half-life) of selected PAHs were developed with depth in deep and shallow waters and sediments. The half life periods in the deep waters (over 100 m) are about twice as long as those in the shallow areas that are 100-150 m deep, and almost 2.5 times as long as those in the top layer (0-10 m). • In the water column, athracene levels would decrease by 50% within 1-2 days. In shallow sediments the half life is about 5-7 days while in the deep sediments its half life is about 13 days. • The half life of Chrysene in the shallow waters would be over 2.5 years while in the deep water it would be almost 5 years. For pyrene, the half life in the shallow sediments could be as long as 9 years (less than 150 m); while in the deep sediments (over 1000 m), it could be over 16 years.
