Remediation of Beach Oiling
Just three weeks before the Exxon Valdez oil spill, oil spill cleanup was brought under the Occupational Safety and Health Administration (OSHA) regulations governing hazardous waste operations. Thus, cleanup workers, who wore protecting rubber suits and gloves, underwent a decontamination procedure at the end of each work day. Other than concerns about the volatile aromatic "BETX" components of oil mentioned earlier, the material safety data sheet (MSDS) for crude oil refers to polyaromatic hydrocarbons (PAHs), which are known to cause skin cancer. Proper water handling and protective clothing effectively eliminated any threat from PAHs.
The natural elements of wind, rain, and snow gradually dislodge oil from beaches and disperse oil particles, which bacteria degrade over time. While this do nothing approach causes no further disruption of the ecosystem, it is a slow process, especially in sheltered areas. Recovery might not occur for 10-20 years.
The extent of surface oil coverage on the most exposed beaches of PWS decreased to around 20% of the initial level during the winter of 1989-1990. Natural action either dispersed oil back into the water column or forced it into subtidal sediments. Overall, the average removal of subsurface oil during the 1989-1990 storm season was estimated at 55%.7
Background biodegradation due to the presence of hydrocarbon-eating bacteria in the environment varied greatly depending on the location. The mean fractional loss during the first year resulting from natural biodegradation in intertidal sediments was 28% for surface oil and 12% for subsurface oil. Predictions from the OSSM model are that biodegradation either on the beaches or in the water column accounted for as much as 50% of the original spill.7
Cold water washing is performed at low pressure by pumping sea water through fire hose and applying it to oiled beaches at low tide to dislodge oil. Cold water deluge, a variation of this technique, involves pumping sea water to a perforated hose placed parallel to the waterline above an oiled area. In either method the water flushes oil to the waterline where the oil is trapped by boom and recovered by skimmers at high tide. This technique, which works best on fresh oil, is relatively harmless to the environment. But the mere presence of many cleanup workers leads to land surface disruption.
After beached oil has weathered, it becomes more intractable and tar-like. Thus, high-pressure steam cleaners were employed to blast weathered oil from rocky beaches. Although hot water dislodges weathered oil better than cold water, the water at temperatures as high as 140°F sterilizes the beaches, leaving them temporarily void of marine life. High pressure also has the effect of driving oil deeper into subsurface sediment.
Exxon had requested approval to use Corexit 9580 M2, a kerosene-based solvent, as a means of removing oil from rock surfaces. Although in trial applications Corexit did exhibit oil-dissolving capability, containment problems precluded widespread use of the chemical.
Physical removal of oil from beaches either manually or using equipment such a bulldozers can be used effectively to remove oil that has weathered on beaches that is impervious to other methods of removal. However, excessive removal of beach sediments can cause serious erosion, as was the case after the Arrow grounding in Nova Scotia in 1970 that released 3 million gallons of oil, or habitat alteration, as occurred in the Ile Grande salt marsh in North Brittany, France, following the 68 million gallon oil spill of the Amoco Cadiz in 1978.10
Oiled beach sediment and solid wastes collected in PWS and the Gulf of Alaska were either incinerated or buried in an industrial landfill in Arlington, OR. Using the OSSM computer program, it has been estimated that 5.5% of the original oil spilled was recovered in this manner.7
Bioremediation involves the application of fertilizer to enhance the rate of production of naturally-occurring bacteria that feed on oil. By the action of aerobic bacteria, hydrocarbons are completely degraded to carbon dioxide and water, a process called mineralization. This method uses bacteria that are already in the environment, although the long-term effects of artificial fertilizers on the environment are not known.
In May of 1989, Exxon conducted field tests of moderately oiled beaches with a liquid oleophilick fertilizer that adhered to the oil covered surfaces and a slow-release solid water-soluble fertilizer. After toxicological screening revealed the process to be safe and effective, EPA granted approval for a large-scale application of nutrients to Alaskan beaches. Inipol,l the liquid fertilizer applied to beaches, contains 2-butoxyethanol, which can be toxic to mammals.
During July-September 1989, about 70 miles of shoreline in PWS were treated with two kinds of nitrogen- and phosphorus-bearing fertilizers to boost indigenous bacterial populations. While the initial results were inclusive, the data has been under evaluation by Exxon scientists. Measuring changes over time in the oil composition relative to a stable, high-molecular-weight hydrocarbon present in the oil when spilled allows quantification of the rate and extent of oil biodegradation. While pristane and phytane have been used as non-degraded markers in analyses of other oil spills, these two hydrocarbons were rapidly biodegraded. Instead, hopane, a C30 pentacyclic hydrocarbon, was selected as an internal conserved standard. The most abundant hopane in Alaskan North Slope crude oil is resistant to biodegradation for years. Hydrocarbon/hopane ratios have suggested that the addition of fertilizers accelerated biodegradation over background rates by 3.7-5.2 times for a one-month period following fertilization. Component compositions are determined by gas chromatography-mass spectrometry (GC/MS), vide infra.11