This phase of an oil spill involves those ac-tions taken to recover spilled oil from the affected environment as well as the monitoring activity associated with determination of the effectiveness of the cleanup operation. It includes those actions taken to mitigate damage cause by the spilled oil, and to dispose of the recovered oil in an en-vironmentally acceptable manner.

REMOVAL.Removal of spilled oil and oil derivatives may be accomplished several ways, including:

1. Allowing evaporation to take place (gasoline and JP-4).

2. Use of physical removal methods such as manual collection or collection by mechanical equipment, such as skimmers.

3. Removal by fostering biodegradation.

4. Removal by burning.

5. Removal by dispersion (emulsification).

6. Pumping of oil in land spills.

Because of effects which are detrimental to the environment, method 4 is not recommended, or practiced, by the Navy unless there is a direct threat to human life and property. Because of the lengthy reaction time involved, and because of the possibility of toxic by products, method 3 is not practiced nor recommended as a desirable Navy practice. However, it may occur, and can con-stitute a final polishing action if all the oil is not removed by physical means.

In addition, gelling agents (chemicals which convert the spill to a semisolid mass) or sorbent materials such as straw, polyester plastic shavings, or polyurethane foam may be used to help the subsequent manual or mechanical removal of a spill.

PHYSICAL REMOVAL METHODS.The Navy prefers physical-mechanical methods of removal, and has designated the types of skim-mers for use with Navy spills in various locations.

1. Small Skimmers. The small unit which is designed for use in congested harbor areas is based on the weir principle. The weir depth of these skimmers is controlled by adjusting the flow rate of the attached pump. As the flow rate is increased, the fluid is removed from the rear buoyancy chamber, tipping the unit clockwise, and thereby increasing the weir depth. Decreas-ing the flow rate allows the buoyancy chamber to fill, tipping the unit counterclockwise, and thereby reducing the weir depth. This unit is most effective in a stationary mode where it is posi-tioned and the oil directed to it.

2. Medium Skimmers. The medium skimmer selected by the Navy is an endless belt unit. It is operable from a pier via handheld controls. The principle of operation is shown in figure 8-4. The rotating belt submerges the oil and directs it to the collection well where it concentrates and from which it eventually is pumped to a temporary storage. This principle is entitled the dynamic in-clined plane (DIPt m).

3. Large Skimmers. The large skimmer selected for use by the Navy is a larger version of the medium skimmer (DIPtm). This unit is vessel-mounted for use in protected open waters, and is quite effective even in choppy water in that it overruns and submerges the oil layer before col-lecting it. A rotating belt directs the oil to the col-lection well.

4. Suction Based Skimmers. Other commer-cially available units for oil removal are based on suction, either taken directly off the surface of the water or by the development of a submerged vortex. Since these units are highly susceptible to wave action and clogging, they work best in calm, debris-free waters, and with thick oil layers. They are not extensively used for Navy spills.

5. Sorbent Surface Skimmers. These units use an endless belt, hose, or rotating drum, the sur-face of which absorbs the spilled oil from the water surfaces. The concept is applied in large, craft-mounted units for large spills and in smaller units using an endless, hose-width belt. The ab-sorbed oil is conveyed to temporary storage tanks where it is squeezed from the belt or wiped from the drum or disc.

6. Manual Methods. Occasionally, manual removal methods are used in the Navy. Manual removal processes involve the physical pickup of the oil from shoreline areas with the use of sor-bent materials, pitchforks, and/or shovels. They also include in water removal operations such as that mounted for small shipside spills in which the Mark I Spill Control Kit is employed. In this instance, herder chemicals may be used to retard spreading of the spill, and hand-held polyurethane absorbent pads or mops are used to sorb and remove the oil. The pads are squeezed out with conventional mop wringers.

Chemical Removal Methods.Chemicals should not be used to emulsify, disperse, solubilize, or precipitate oil whenever the protec-tion or preservation of freshwater supply sources, major shellfish or finfish nurseries, harvesting, grounds, passage areas, or beaches is a prime concern.

Such chemicals should only be used in those surface water areas and under those circumstances where preservation and protection of water related natural resources is judged not to be the highest priority or where a choice as to resource preser-vation may make the use of such materials a necessary alternative. When chemical compounds are used in connection with oil cleanup, only those compounds exhibiting minimum toxicity toward aquatic flora and fauna should be used. The EPA is now developing, and will soon issue, a standard procedure for determining the toxicity of such chemicals.

Now lets describe some of the chemical removal methods used.

1. Dispersants. Dispersants (emulsifiers) are surface active agents which foster the development of oil/water emulsion. They may be ionic or non-ionic in nature and are typically mixed with stabilizers, to preserve the emulsion formed, and solvents for cold weather use when surfactant viscosity is reduced. A typical dispersant is about 70-80% solvent, 10-15% surfactant and 10-15% stabilizer.

The use of dispersants exposes a great surface area for microbiological attack. However, many

Figure 8-4.Principle of Operation of Dynamic Inclined Plane (DIP) Skimmer.

of the surfactants are not degradable; and they, or the materials with which they are mixed, may be toxic to microorganisms and aquatic species. By dispersing, they distribute the oil throughout the water column, extend its area of influence con-siderably, and have a resultant adverse biological impact. Also, dispersant may have a short effec-tiveness period; and the oil is released and resur-faces. In fact, dispersion is not really a removal method but rather one of spreading the oil and reducing its visibility.

2. Sinking Agents. Sinking agents are materials such as clay, fly ash, sand, or crushed stone which when applied to spilled oil will sink it. Sunken oil will cover and smother or taint the bottom (benthic) organisms, including shellfish. Additionally, it will move and resurface as a result of turbulence or microbial degradation. For this reason the use of sinking agents is prohibited by Federal regulations.

3. Gelling Agents. These materials absorb, congeal, entrap, and fix the oil to form a semi-rigid or gelatinous mass, which may be more easily recovered, or will inhibit the spread of the spill. Gel agents include soap solution, wax, fatty acids, and various polymers.

4. Burning Agents. The loss of volatile components and the incorporation of water make oil spills difficult to ignite and sustain in the burning condition. The use of burning agents is essential if burning is to be pursued, and approved, as a disposal means. These agents contain combustion promoting and sustaining chemicals. Their use may be authorized by the OSC when it will prevent or substantially reduce hazard to life or property. Such instances are rare in inland waters, and burning should be avoided.

DISPOSAL.As oil is recovered from the spill area, it must be pumped to a storage area or container where oil/water separation is initiated or continued. Gravity separation, centrifugation, and other separation techniques are available in commercial equipment. The concentrated oil is then removed to transport facilities and conveyed to recycle or disposal sites.

Once oil has been removed from the spill site, the major battle may have been won; but the conflict goes on, because unless the oily waste or oiled debris is properly disposed of by the Navy activity or contract operator, it can and will become a problem at the disposal site. The conventional disposal methods listed in Table 8-2, for example, may allow the oil to recontaminate surface or ground waters, degrade the air quality, or present fire hazards. Damages re-sulting from any unauthorized disposal of oil by the Navy or its contractor may lead to litigation.

The disposal options are essentially limited to (1) reuse; (2) disposal by soil cultivation tech-niques; (3) controlled burning; or (4) placement in approved sanitary landfills.

Reuse of the oil collected from the spill is to be preferred where it is possible. The recovered oil may be re-refined and recycled for beneficial use. Re-refining facilities are not always readily accessible from spill sites, but the possibility of reuse should always be considered.