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

S0300-A6-MAN-060Grabs, clam shell buckets, power shovels, drag lines or back hoes can remove viscous or weatheredoil, oily debris or oil-saturated sorbents pooled or collected near shorelines and piers.Oil that has washed ashore and contaminated the shoreline is nearly impossible to remove withthe skimmer systems unless it is very plentiful in deep pools or layers. Once ashore, oil usually isremoved by personnel operating mechanized or manual equipment. Heavily soaked beaches canbe cleaned by removing the oil-soaked sand with front-end loaders, graders, dump trucks andbulldozers. Grabs and backhoes are excellent tools for picking up oil-covered rocks that are tooheavy to be moved by hand. Shoreline cleanup is addressed in greater detail in Chapter 7.5-2.5.4 Vortex Skimmers. Vortex skimmers draw oil and water over a weir into a separationchamber by creating a vortex with a rotating paddle. Some water separates from the oil as itpasses over the weir. Additional water is separated from the oil by centrifugal force and gravity asthe water is forced to the outside of the separation chamber, while the oil rises and moves to thecenter of the chamber to be drawn into a storage tank. Vortex skimmers work best in calm waterswhere wave action is minimal. Figure 5-9 shows a typical vortex skimmer system.5-2.5.5 Screw Pumps. Screw pump skimmers like those shown in Figure 5-10 are used primarilyto recover viscous oils. The adjustable float keeps the weir inlet at the oil-water interface.Screw pumps tolerate debris but are quite sensitive to wave action.5-3 OIL RECOVERY OPERATIONSFigure 5-9. Vortex Skimmer.The choice of recovery devices and methods depends on oil characteristics, spill size and location,weather, sea conditions, shoreline geography and, above all, availability. Skimmer performancevaries widely with oil viscosity. Most skimmers have a range of viscosities for which they aremost effective. General skimmer applicability is shown below:5-13