Exxon Valdez - Legacy of a Spill

Thursday
May 13, 1999

Legacy of a Spill: Stories | Illustrations | Photos


Researchers track crude's wandering trail

By DOUG O'HARRA
Daily News reporter



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Tracking the fate of the oil from the Exxon Valdez begins at the moment of grounding - 12:04 a.m. on March 24, 1989. Within five hours of striking Bligh Reef, most of 11 million gallons had gushed out and surfaced. The slick spread relentlessly - "amoeba-like," according to one report - to cover about 120 square miles of open water near the tanker. For most of three days, the winds were calm. A significant fraction of the oil's volume would evaporate and be gone by the end of this period.

"Crude oil is an extremely complex mixture of thousands of organic compounds," wrote Douglas Wolfe, head of the Bioeffects Assessment Branch of the National Oceanic and Atmospheric Administration's National Ocean Service, who joined 11 co-authors in a widely quoted analysis published in 1994 on the overall fate of the spilled oil. "A wide variety of physical, chemical, and biological processes begin almost immediately to transport and transform crude oil when it is introduced into the marine environment."

As the oil evaporated, Wolfe and his co-authors noted, other components began to dissolve and disperse into the water. Some others were absorbed by particles and sank; some were broken down by bacteria and ingested by living creatures. Oil also washed toward the beaches.

The process accelerated on March 26, when a storm hit in late afternoon with 20 to 25 knot winds that gusted up to 70 knots. Driven by this wind, churned by waves, the slick rapidly swept southwest, reaching Naked, Eleanor, Smith, Ingot and Knight islands. Within four more days, the slick swept by Latouche Island and began to float out Montague Strait into the Gulf of Alaska. By then, most floating oil was transforming into "mousse" - a goopy emulsion containing up to 67 percent water and, because it was so frothy, often three times the volume of pure oil.

"For the next three weeks, oil was repeatedly deposited, refloated, and redeposited," Wolfe wrote. "During this period, floating oil continued to drift from Prince William Sound into the Gulf of Alaska, where it floated in windrows and mousse ... and grounded on the exposed headlands of the Kenai Peninsula."

The spill reached the Chiswell Islands on the Kenai Peninsula's outer coast by April 2. It reached major bird nesting sites on the Barren Islands at the mouth of Cook Inlet by April 11. By the end of April, mousse was drifting into the Shelikof Strait, where it began hitting beaches of Kodiak Island and the Alaska Peninsula, eventually reaching sites 600 miles from Bligh Reef.

Yet, even as the slick spread farther, oil was disappearing. By May 1, about 20 percent - mostly highly volatile and toxic compounds - had evaporated into the air where it oxidized. Another 20 to 25 percent had dispersed into the ocean, where it rapidly degraded through natural processes, according to Wolfe.

Meanwhile, some floating oil was recovered through skimmers or destroyed in efforts to burn it - about 8 percent, according to Wolfe. Between 7 percent and 11 percent (800,000 to 1.2 million gallons) beached outside the Sound, - hitting portions of beaches along the outer Kenai Peninsula, Kodiak and the Alaska Peninsula.

This oil "was very different from that beached within PWS," Wolfe wrote. "The continuous slick of liquid oil had broken up into streamers and patches of floating mousse, which stranded as discrete patches instead of blanketing beach surfaces."

Prince William Sound took the brunt because the oil was fresher. By early summer of 1989, an estimated 41 percent of the spill's volume - nearly 5 million gallons - had washed ashore there, fouling to some degree nearly 500 miles of beaches.

This was the southwestern Sound's season of death - the images of floating carcasses and oiled animals pressed indelibly into public memory. With the coming of spring that year, life bloomed, herring spawned, animals foraged in fouled waters. Fishing seasons were cut back, subsistence activities suspended. Scientists scrambled into the field and worked around the clock. Hundreds of people and boats converged to clean beaches and protect hatcheries.

While direct exposure to floating oil could harm animals - destroying the insulation of sea otter fur or the buoyancy of a bird's plumage - the ingestion of hydrocarbons dissolved in the sea was also feared.

A four-year study of the Sound's water quality a decade earlier had found virtually no hydrocarbons, according to federal chemist Jeff Short.

"It was whistle clean," he said. "It was one of the most pristine environments on Earth."

Because of that earlier finding, conducted as part of the preparations for opening the trans-Alaska pipeline system, the spill offered a unique opportunity for science to track the effect of oil on marine life, Short said.

Within a week of the spill, Short, biologist Pat Harris and a boat crew began chasing the slick, by then about a millimeter thick and spreading fast. They found it first in Northwest Bay on Eleanor Island, where the fumes almost knocked them out. Over the next five weeks, they repeatedly visited 32 places, taking 501 water samples. Most of the samples were analyzed for traces of 65 separate components from crude oil, including 43 toxic polynuclear aromatic hydrocarbons, or PAHs.

PAHs are heavier cousins to more toxic and lighter aromatics like benzene and toluene, which dissipate much more readily.

If the work was highly technical and arcane, the view was starkly simple.

"There was dead stuff all over the place," he said. "We saw lots of dead marine mammals, lots of floating birds."

Among other things, the researchers found that PAHs readily dispersed into the water column to depths of about 15 feet during the first two weeks. As weeks passed and levels fell off, the heaviest concentrations were found off heavily oiled beaches.

"Our data ... demonstrate that PAHs from Exxon Valdez crude oil were available to subsurface marine fauna during the first few weeks after the oil spill, especially in near-shore, near-surface waters that are particularly productive biologically," Short and Harris later reported.

Then, as the amount of oil that could be directly detected disappeared into the background of the ocean, Short and Harris relied on caged mussels to track the hydrocarbons.

Mussels filter about 88 gallons of sea water each day, the researchers later wrote in an academic article. "Hence, the volume of seawater effectively sampled by mussels in one month can be 10,000 times greater than sampled for direct chemical analysis."

They concluded that submerged oil dispersed throughout seawater to about 75 feet during the first few months, then gradually became limited to waters off heavily oiled beaches. "This submerged oil was clearly available to mussels and possibly to other fauna," they wrote.

By the end of this summer, human effort and nature had removed much more oil. Moderate to heavy oiling was found on only 85 miles of Prince William Sound beaches in the fall survey by the Shoreline Cleanup Assessment Team. Outside the Sound, the picture was better - 14 miles of heavy to moderate oiling in the Kenai or Cook Inlet area, 1.3 miles in Shelikof Strait and on Kodiak.

By the fall of 1992, Wolfe and 11 co-authors estimated a "mass balance" for the entire spill. By their calculations, about 70 percent of the spill's volume (about 7.6 million gallons) had by then disappeared - evaporated into the air and biodegraded on shore or in the ocean.

About 14 percent had been recovered or destroyed through cleanup. Perhaps 1 percent had dispersed into the ocean, spreading out into the Gulf of Alaska at extremely low concentrations.

But 13 percent - reflecting about 1.4 million gallons of the original volume - remained in mud and sand and gravel, largely in the Gulf of Alaska but also in sediments in Prince William Sound. And 2 percent - 217,000 gallons - remained beached at scattered locations.

Between 1991 and 1993, the amount of oil on the Sound's beaches and in its sediments gradually declined by about half, with the rate of decline slowing dramatically in the second year, according to the final report on shoreline oiling by James Gibeaut of the University of Texas at Austin and Ernie Piper, then an employee of the Department of Environmental Conservation.

In the summer of 1993, state survey crews visited 45 sites and found oil in various stages of weathering at 217 surface locations, affecting about three miles of shore. They also found oiling buried in sand, mud and gravel at 109 locations along about 4.3 miles.

"Surface oil that remained in 1991 has proven to be resilient," they concluded. Even though a shoreline may be exposed to storms and big surf, they said, surface oil has survived in the shelter of large boulders, bedrock outcrops and bedrock fractures. "Reduction since 1992 has been incremental and mostly related to treatment," they wrote.

Outside of the Sound, where most of the beached oil was considered gone within the first year or two, a few surveys have since found scattered problems. In 1994, scientists visited six oiled sites on the Alaska Peninsula and found relatively unweathered oiled at five. In 1995, state crews visited 30 sites in Kodiak that had significant oiling in 1990-91 and found only trace amounts.

Another survey is planned for Kenai and Katmai coasts this next season. A survey may take place in Prince William Sound in 2000 or 2001.

Exxon scientists and officials agree that a tiny fraction of the original oil remains on beaches. But they say the oil poses no significant threat to marine life.

The dozens of known oiled beachs and mussel beds are likely to represent only a portion the total number that remain damaged, the government scientists say. Since 1993, no one has attempted a comprehensive survey or calculated the volume of remaining oil.

"We don't know where all the sites are that still have oil and we don't have any numbers on the amount," Exxon Valdez Oil Spill Trustee science coordinator Stan Senner said. "You might ask, 'Why not?' And the answer is that it's really expensive work. We've focused more on fish and wildlife rather than on quantifying the oil."

"I would say that, in general, most places are clean, or recovered," added Dianne Munson, a state environmental specialist who performed much of the shoreline surveying in the Sound. "But there are some areas, a handful of spots, where it has just been incredibly persistent."

If you know where to look, she said, "It still smells. It still stinks."

* Reporter Doug O'Harra can be reached at do'harra@adn.com

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Legacy of a Spill: Stories | Illustrations | Photos

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