Dispersant Application

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This photo is a side view of a DC-4 airplane applying dispersant during dispersant application methods tests by the Southern California-Petroleum Contingency Organization and the American Petroleum Institute (API), in September 1978 and 1979. The dispersant has been dyed red to make it more visible to observers. Credit: NOAA
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Dispersant application from a C-130 Hercules airplane using an Aerial Dispersant Deployment System (ADDS). The dispersant has been dyed red for experimental purposes. Credit: NOAA
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A helicopter applying dispersant using a bucket spray unit (side and top views). In the top photo, a mist of undyed dispersant is visible behind the bucket spray unit. Credit: NOAA

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In this photo, showing an overhead view of the dispersant application, a trail of white dispersant mist is visible behind the helicopter and bucket spray unit. The red-brown streak on the water surface is the spilled oil that is being treated. Credit: NOAA
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Dispersant application from a ship. Credit: NOAA
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In the photo, as the vessel applies dispersant, its wake is parting the oil slick, leaving behind a swath of clear water. Clearing from boat wakes is sometimes wrongly interpreted as a sign that a dispersant application has worked. Credit: NOAA

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The photos below show how change over time in the appearance of a slick treated with dispersant, compared with an untreated slick, may indicate that the dispersant is working. Both photos on this page were taken during an experimental spill of about 1 cubic meter (265 gallons) of a medium Venezuela Lago Medio crude oil. In this experiment, one slick of spilled oil was treated with dispersant; a second, otherwise similar control slick was left untreated; observers then compared the appearance of the two slicks. This experiment took place offshore of Newfoundland, Canada, from October 18 to 21, 1981. Pictured directly below is the control slick (which was not treated with dispersant) about 1 hour after oil release. In this photo, dark patches of oil and lighter patches of sheen are visible on the water surface. Credit: NOAA
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The photo shows the remains of the dispersant-treated slick as seen 1 hour later. A subsurface plume of dispersed oil is visible as light-brown patches below the water surface. In this experiment, the area of the treated slick was greater than the area of the control slick. This difference is in accord with the results of other experiments, which have indicated that dispersants appear to modify the spreading rates of oils, and that within a few hours, treated slicks cover much larger areas than control slicks. Credit: NOAA
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In this experiment, 20 cubic meters (5,300 gallons) of Sture blend crude oil was weathered for 3.5 hours, then treated with dispersant. In the top photo, a helicopter applies 800 liters (5 barrels or 211 gallons) of a dispersant, COREXIT 9500, to the oil. Because the weather was cloudy and the oil formed a very dark emulsion, observers in the application helicopter found it difficult to differentiate thicker, emulsified oil and thinner oil films and sheens. Credit: NOAA

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Researchers reported that despite poor conditions for visually observing dispersed plume development, oil was dispersed. They documented the presence of a dispersed subsurface plume of oil by taking water column measurements. Also visible during this experiment was a phenomenon known as the "herding" effect. This effect results from the surfactant action of dispersants, which exerts a horizontal spreading force on thin oil films. The herding effect can make a slick appear smaller in area, and may even cause a slick to seem to disappear temporarily from the water surface. In the photo below, the herding action of the dispersant has produced a distinct, V-shaped area of clear water behind the helicopter. Credit: NOAA
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This series of three photographs shows a test dispersant application during the Exxon Valdez spill in 1989. This photograph shows the third in a series of applications of the dispersant COREXIT 9527 to thick, dark oil. Sheen is being driven over areas where dispersant has been applied, as wind and currents move the surface oil faster than the subsurface dispersed oil (which is moving by current alone). No subsurface plume is visible. (Time: 14:52) Credit: NOAA
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About 30 minutes after the third dispersant application, the treated slick has begun to break up; remaining surface oil is now visible as red-brown streaks on the water surface. A subsurface plume has formed, and is visible as milky subsurface areas below the oil streaks. (Time: 15:24) Credit: NOAA

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An hour after the previous photo was taken, only the section of the slick that was not treated with dispersant still remains on the surface, where it is visible as a streak of brown surface oil to the left of the milky subsurface plume. The surface oil, which is being pushed by the wind, is moving faster than the subsurface plume of dispersed oil. (Time: 16:41) Credit: NOAA
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On December 15, 1995, 117 cubic meters (31,000 gallons) of a light crude oil leaked from a platform 35 miles south of the Texas coast, into water deeper than 10 meters. At 15:50 on December 16, a DC-4 aircraft began spraying the dispersant COREXIT 9527 from 50 feet (15 meters) above the water. Oil slicks and plumes can vary in appearance for reasons like sun angle, characteristics of the oil, time of day, sea state, and weather. About 20 minutes after spraying, this slick appeared to have a "glossy" look. The DC-4 pilot reported, "The oil at first appeared as a reddish orange. After spraying about 10 to 15 minutes, the oil color appeared to change to a much darker reddish-brown. No milkiness was observed." The photos below were taken by an observer in a helicopter travelling at 500 feet (152 meters) above the water. Credit: NOAA
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Forty minutes after the dispersant application, the effects of the dispersant began to be visible. The observer aboard the helicopter noted, "The lighter areas seemed to dissipate quickly after spraying. The heavy orange area seemed to be holding its shape, but water could now be seen starting to cover the outer 20 feet [6 meters] or so around the perimeter." Credit: NOAA

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At 07:00 the next day, the observer on the helicopter reported, "The spill had split in half. The outer area of the larger spill seemed to be breaking up with silver traces leading out in the direction the wind was blowing. Only the center 100 feet [30 meters] was brown in color." In the photo, a subsurface plume of dispersed oil is visible as an extensive milky area surrounding the remaining streaks of surface oil. Credit: NOAA
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As a vessel travels through a slick of spilled oil, its wake can produce a swath of clear water, either by physically parting the oil or by mechanically dispersing it (by breaking it up into small droplets). Such a swath of clear water behind a dispersant application vessel (as is visible in the photo) can give the appearance that the dispersant is working (that is, a "false positive"). However, unlike chemically dispersed oil, mechanically dispersed oil eventually will recoalesce and float to the surface. Credit: NOAA
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It's important to report birds, turtles, and marine mammals that you observe in the dispersant application area, since many of these animals may be harmed by direct contact with dispersants. Here are three examples showing how marine mammals may appear when viewed from an aircraft. The photo shows a herd of manatees (Trichechus manatus) swimming below the surface. Note their paddle-shaped tails. Credit: NOAA

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Whales may form patterns in the water that can be confused with dispersing oil. For example, pale gray patches on the backs of these pilot whales (Globicephala sp.) could be taken to be subsurface plumes of dispersing oil (which typically appear milky in color). Credit: NOAA
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This photo shows a loggerhead sea turtle (Caretta caretta) swimming below the surface. Credit: NOAA