Tuesday, March 24, 2009

20 Years Ago Today: Exxon Valdez Oil Spill

The Exxon Valdez oil spill occurred in Prince William Sound, Alaska, on March 24, 1989. It is considered one of the most devastating human-caused environmental disasters ever to occur at sea. As significant as the Exxon Valdez spill was, it ranks well down on the list of the world's largest oil spills in terms of volume released. However, Prince William Sound's remote location (accessible only by helicopter and boat) made government and industry response efforts difficult and severely taxed existing plans for response. The region was a habitat for salmon, sea otters, seals, and seabirds. The vessel spilled 10.8 million U.S. gallons of Prudhoe Bay crude oil into the sea, and the oil eventually covered 11,000 square miles of ocean.

The oil tanker Exxon Valdez departed the Valdez oil terminal in Alaska at 9:12 pm on March 23, 1989 bound for Washington. A harbor pilot guided the ship through the Valdez Narrows before departing the ship and returning control to Joseph Jeffrey Hazelwood, the ship's master. The ship maneuvered out of the shipping lane to avoid icebergs. Following the maneuver and sometime after 11 pm, Hazelwood departed the wheel house. He left Third Mate Gregory Cousins in charge of the wheel house and Able Seaman Robert Kagan at the helm, both of which were not given their mandatory 6 hours off duty before their 12 hour duty began. The ship was on autopilot, using the navigation system installed by the company who constructed the ship. The outbound shipping lane was covered with icebergs so the ship's captain, Hazelwood, got permission from the coast guard to go out through the inbound lane. The coast guard was given the task of ensuring safe passage but failed to keep watch over the Valdez; subsequently the ship struck Bligh Reef at around 12:04 am March 24, 1989.

According to official reports, the ship was carrying 53.1 million gallons of oil, of which 10.8 million gallons were spilled into the Prince William Sound. This figure has become the consensus estimate of the spill's volume, as it has been accepted by the State of Alaska's Exxon Valdez Oil Spill Trustee Council, the National Oceanic and Atmospheric Administration, and environmental groups such as Greenpeace and the Sierra Club. Some groups, such as Defenders of Wildlife, dispute the official estimates, maintaining that the volume of the spill has been under reported.

The first cleanup response was through the use of a dispersant, a surfactant and solvent mixture. A private company applied dispersant on March 24 with a helicopter and dispersant bucket. Because there was not enough wave action to mix the dispersant with the oil in the water, the use of the dispersant was discontinued. One trial explosion was also conducted during the early stages of the spill, in a region of the spill isolated from the rest by another explosion. The test was relatively successful, reducing 113,400 liters of oil to 1,134 litres of removable residue, but because of unfavorable weather no additional burning was attempted in this cleanup effort. Mechanical cleanup was started shortly afterwards using booms and skimmers, but the skimmers were not readily available during the first 24 hours following the spill, and thick oil and kelp tended to clog the equipment.

Exxon was widely criticized for its slow response to cleaning up the disaster and John Devens, the mayor of Valdez, has said his community felt betrayed by Exxon's inadequate response to the crisis. Working with the United States Coast Guard, which officially led the response, Exxon mounted a cleanup effort that exceeded in cost any previous oil spill cleanup. More than 11,000 Alaska residents, along with some Exxon employees, worked throughout the region to try to restore the environment.

Because Prince William Sound contained many rocky coves where the oil collected, the decision was made to displace it with high-pressure hot water. However, this also displaced and destroyed the microbial populations on the shoreline; many of these organisms (e.g. plankton) are the basis of the coastal marine food chain, and others (e.g. certain bacteria and fungi) are capable of facilitating the biodegradation of oil. At the time, both scientific advice and public pressure was to clean everything, but since then, a much greater understanding of natural and facilitated remediation processes has developed, due somewhat in part to the opportunity presented for study by the Exxon Valdez spill. Despite the extensive cleanup attempts, a study conducted by NOAA determined that as of early 2007 more than 26 thousand U.S. gallons of oil remain in the sandy soil of the contaminated shoreline, declining at a rate of less than 4% per year.

Both the long-and short-term effects of the oil spill have been studied comprehensively. Thousands of animals died immediately; the best estimates include 250,000 to as many as 500,000 seabirds, at least 1,000 sea otters, approximately 12 river otters, 300 harbour seals, 250 bald eagles, and 22 orcas, as well as the destruction of billions of salmon and herring eggs. Due to a thorough cleanup, little visual evidence of the event remained in areas frequented by humans just 1 year later. However, the effects of the spill continue to be felt today. Overall reductions in population have been seen in various ocean animals, including stunted growth in pink salmon populations. Sea otters and ducks also showed higher death rates in following years, partially because they ingested prey from contaminated soil and from ingestion of oil residues on hair due to grooming.

20 years after the spill, a team of scientists at the University of North Carolina found that the effects are lasting far longer than expected. The team estimates some shoreline habitats may take up to 30 years to recover. Exxon Mobil denies any concerns over this, stating that they anticipated a remaining fraction that they assert will not cause any long-term ecological impacts, according to the conclusions of 350 peer-reviewed studies. However, a study from scientists from NOAA concluded that this contamination can produce chronic low-level exposure, discourage subsistence where the contamination is heavy, and decrease the "wilderness character" of the area.

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