Lowcost Cleanup Methods for Coastal Sediments and Waterways Impacted by the BP Oil Spill of 2010
TASA ID: 897
Several issues are associated with the migration of hydrocarbons in the environment: 1) Natural microbe (aerobes) using oxygen for respiration will eventually consume most of the crude oil released by the BP Oil Spill of 2010. 2) Without a ready source of oxygen, the crude oil will not naturally attenuate very quickly. 3) As the crude oil plume dissolves into the Gulf of Mexico waters, for every kg of crude oil present, approximately 3 kg of oxygen will be required for microbes to completely mineralize the crude oil dissolved in the ocean water into the end products, carbon dioxide and water.
Oxygen in the atmosphere is 20.9%. The solubility of oxygen in fresh water at one atmosphere at 25°C is 8.2 mg/L. Sea water at the same temperature, due to high levels of dissolved salts, has even less carrying capacity for dissolved oxygen, which is 7.1 mg/L. As the naturally occurring aerobic microbes consume the crude oil as food in sea water, the dissolved oxygen in the Gulf of Mexico will decrease based on the volume of hydrocarbons dissolved in sea water. Dissolved oxygen will be consumed by the aerobic microbes as part of the natural degradation process in sea water. When dissolved oxygen reaches less than 2 mg/L, major fish kills will occur, and dead zones will be more commonplace throughout the Gulf of Mexico.
DISSOLVED CONTAMINATION
Although most of the media is concerned about the obvious floating free product associated with the BP Oil Spill, it is the dissolved contamination that will remain for a long period of time and continue to volatilize, generating the crude oil odors, long after the free product has been mostly cleaned up from the surface of the air-sea interface. An interesting experiment known as DeepSpill, conducted in 2000, was performed off the coast of Norway and sponsored by 23 oil companies as well as the U.S. Mineral Management Service (MMS). In four different two-hour tests, 60 cubic meters (15,850 gallons) of nitrogen gas, marine diesel oil, crude oil and natural gas were released at 844 meters (2,769 feet). For the diesel test, of the 60 cubic meters that were released into the ocean, only between 1 and 17 cubic meters, the lower and upper estimate ranges, were observed on the surface. The difference was ascribed to evaporation and natural dispersion. This also suggests a significant amount of hydrocarbons become dissolved in the ocean water. This is likely the case with the BP Oil Spill, and the ocean will have high levels of dissolved hydrocarbons in the water for many years, which will still impact beaches and property values, as well as the food chain and fishing industry for decades.
LOW COST CLEANUPS
A triage system must be performed to evaluate the seriousness of the threat of the BP Oil Spill. For some properties, there will be no need for concern. For other sites, monitoring of groundwater or soil vapor might be appropriate to verify that there are limited exposure pathways. In yet other cases, crude oil as floating product may have impacted some coastal communities where sources of drinking water might be threatened.
Low-cost cleanups use methods for remedial measures which eventually clean up from the BP Oil Spill. Crude oil contains a variety of toxic compounds, many carcinogenic. Therefore, if the concentrations of specific compounds are deemed to be hazardous or above regulatory accepted levels associated with protecting human health, wildlife and environmental resources, (including water supplies), cleanup of the crude oil is recommended.
For free product, sphagnum (peat moss) works reasonably well as a natural and inexpensive sorbent. Biosurfactants have been used successfully with soil washing of coarse-grained sediments, such as on a beach.
Systems using low-cost methods should be considered for cleanup. One method can use oxygen concentrators to sparge oxygen into beach sands for rapid microbial degradation of crude oil. Phytoremediation (using specific plants) can be planted to uptake the impacted groundwater. Phytoremediation has been demonstrated on numerous sites nationwide. The process is slow (several years), but the costs are relatively modest, and the end product is a forest of poplar trees or field with mustard grass.
Mychoremediation uses mushrooms to consume or breakdown the toxins in crude oil. More than 120 novel enzymes have been identified from mushroom-forming fungi, and lower molecular weight hydrocarbons have been degraded using mushrooms. Although mychoremediation has not been used extensively in the past, a passive application in Gulf Coast communities may be appropriate.
Other more aggressive in-situ techniques can be used for cleanup as well, such as chemical oxidizers (Fenton's Reagent, ozone, Perozone, activated sodium persulfate, etc.) which degrade the crude oil into carbon dioxide and water. Active water pumping and soil washing with surfactants will probably be used for more aggressive cleanups in the more impacted areas.
The local regulators will define what is considered appropriate to clean up. Some concentrations of hydrocarbon contamination will be considered safe to monitor and allow natural attenuation be the main cleanup method. However, in areas where free product or high concentrations of dissolved crude oil exist near coastal drinking water supplies, if the contamination is not cleaned up, it will likely spread out over time, making future cleanups even more time-consuming and costly.
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