U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060EXAMPLE 2-1During an overflight, the spotter estimated that a slick of free oil measuring 1 mile x 2 milessquare consisted of patches totaling 15 percent mousse, 25 percent black-appearing oil and 60percent iridescent sheen. Fifty percent of the mousse was water.Contribution of mousse: 885,000 gal/sq mi x 2 sq mi x 0.15 x 0.50 = 132,750 gallons oilContribution of black appearing oil: 88,500 gal/sq mi x 2 sq mi x 0.25 = 44,250 gallons oilContribution of iridescent sheen: 265.5 gal/sq mi x 2 sq mi x 0.60 = 319 gallons oilTotal gallons estimated = 132,750 + 44,250 + 319 = 177,319 gallons oilThese calculations illustrate two important points. Although the sheen covered 60 percent of theaffected water surface, it accounted for less than 1 percent of the oil. The type of oil should betaken into account when deploying skimmers. Skimmers will engage much more oil when operatingin black/brown patches of oil than in a sheen.The other point is that although a very large proportion of mousse is water and was not includedin these calculations, water will be retrieved as part of the mousse during an oil spill response.The volume of oily water emulsion (mousse) that must be handled is nearly twice the volume ofoil spilled. Once mousse begins to form, skimmer and waste oil storage capacity requirementsincrease dramatically.2-5.3 Oil Slick Movement. When the projected slick track is known, assets may be deployed efficientlyto capture the oil and areas needing protection may be identified.Wind, tides, currents, wave action and weathering of oil all affect oil slick movement. Becausemost of these parameters may be measured or are predictable, computer programs have been writtento forecast free oil movement. While not an exact science, accuracy of oil spill trajectory forecastskeep improving. Government and commercial services are available that offer thisinformation. Regional Response Teams and NOAA can make arrangements for such services.Rough estimates of free oil movement are made by summing wind and current drift vectors. Ingeneral, oil spills are influenced mostly by prevailing wind and water movement. For rule ofthumb calculations, the wind-drift vector is three percent of true wind velocity, in the direction oftrue wind. The water movement vector is the velocity and direction of prevailing current. The sumof these vectors give an approximation of oil spill movement. Example 2-2 illustrates an estimateof oil slick movement:2-18