AERIAL APPLICATION OF DISPERSANTS—COMPARISON OF SLICK BEHAVIOR OF CHEMICALLY TREATED VERSUS NON-TREATED SLICKS

Abstract

ABSTRACT From June 18 to 22, 1984 two series of dispersant tests were carried out off the Norwegian coast. The first series comprised 2 parallel slicks: one control and one treated with dispersant 2 hours after discharge. The second series comprised 4 parallel slicks: (1) control; (2) dispersant application after 1 hour; (3) oil and dispersant mixed prior to discharge; and (4) dispersant application 4 hours after discharge. Each slick contained approximately 10 m3 of fuel oil. The dispersant applied by aircraft was Corexit 9527. The development of the different slicks was continuously monitored by aerial surveillance using side-looking airborne radar (SLAR), infrared and ultraviolet remote sensing, and vertical color photography as well as video recording for at least 6 hours (first series) and up to 12 hours (second series) after discharge. Dispersion of oil into the water column was investigated by turbidity measurements in the water column and by analyses of oil content in water samples from different depths. Furthermore, emulsion formation and viscosity changes of the surface oil were studied in each slick. Aerial registrations as well as water column measurements show that both the horizontal and vertical spreading of oil was significantly enhanced in dispersant-treated versus non-treated slicks. In the first series, the dispersant-treated slick covered an area 2 to 3 times larger than the control slick a few hours after treatment. Hydrocarbon concentrations in the water column were found to be up to 40 ppm in treated slicks. Viscosity of the surface oil in untreated slicks increased due to emulsion formation, while the viscosity of surface oil in treated slicks decreased, likely due to an emulsion breaking effect of the dispersant.