North Slope oil spill cleanup never easy but usually thorough

Tom Hall

PNA Reporter

Ice, oil and the Arctic. Present in Prudhoe Bay over 280 days per year in varying forms, ice can be boon or bane to oil spill response personnel. Alaska Clean Seas Operations Manager Nick Glover told the Alaska Support Industry Alliance Dec. 11 that ice, in combination with extreme environmental conditions, challenges the ability of oil spill responders and response managers to carry out safe and effective oil spill operations. However, 20 years of research and development projects have helped oil spill professionals to develop effective strategies and tactics for Arctic conditions. Spill responders have learned that their spill response plans must consider three factors.

“First,” said Glover, “you have to understand how the safe behavior of oil is going to be affected by the presence of ice. Second, you have to understand what limitations just the presence of ice has on your ability to respond. How does that control your options? And third, that there are certain seasonal limitations and benefits that have to be incorporated into your spill response plans.”

Oil behavior

Oil spill responders everywhere, but particularly in temperate climates, consider spreading the biggest challenge. “In the Arctic,” Glover said, “it is not as much of an issue because nine months out of the year, there’s a presence of ice and snow. That limits the spreading, which limits the affected area, which allows oil spill responders to plan and effect an immediate response.”

Evaporation and multiplication are opposite sides of a double edged sword. If it’s close to the atmosphere, Prudhoe Bay crude oil can evaporate from 16 to 35 percent in the first 48 hours, but when oil becomes mixed in oil and snow, the evaporation process ceases. Multiplication occurs during evaporation and oil entrains (encapsulates) water droplets. Glover said that North Slope crude oils can multiply to such an extent that the resulting slick can be 75 to 85 percent water content. “That’s an extreme challenge to responders because not all of their tools are going to work on that sort of a problem,” he said.

The process of entrainment, or encapsulation, is a phenomenon of under ice storage. The bottom surface of ice is not smooth, but consists of undulations that form natural cavities.

Thus, oil spilled from something like a sub-sea pipeline would rise to the bottom sheet of ice and fill these convex formations. According to Glover, studies from the late seventies and eighties show that oil from a sub-sea leak would become completely encapsulated in the ice sheet. Then in the spring, the oil would migrate naturally to the surface where it would become available to spill responders.

“What we find is that under ice storage is very significant,” said Glover. Using a 4,000 barrel sub-sea spill as a hypothetical example, Glover said that beneath two feet of ice in December, the spill radius would be about 320 feet. If the same spill occurred in April, the radius would be 200 feet.

“To put it on a larger scale,” Glover said, “one square mile of five foot thick Beaufort Sea ice has a holding capacity of one million barrels.” So a spill four times the size of the Exxon Valdez incident could be contained within one square mile.

Ice presence is the second major factor for consideration by oil spill responders. Ice thickness, bottom founded ice (ice that has grown so deep that it rests on the sea floor), ice stability (lateral movement across the surface of the water), ice concentration, and a springtime phenomenon called overflow, are conditions that influence the ability to respond and decision making. Of these, thickness is the greatest concern.

“Safety is your number one priority when you respond to a spill,” Glover said. “At no point in time are we going to put anybody at risk to respond to an oil spill.” With six to 10 inches of sea ice, responders may use ATVs, snow machines or walk in on foot, and everything is hand carried to the site. Care must be taken not to put too much out there to accumulate waste. “If you go out on eight to 10 inches of ice and put up a 2,500 gallon fast tank and start to fill it, you may find yourself swimming before too long,” said Glover.

As the ice thickens during freeze up, it becomes bottom founded. That allows responders to take heavy equipment out on the ice, where it then becomes a civil project involving the North Slope contracting community and member producers. “This is one of the best conditions for us,” said Glover, “and this exists for over six months out of the year.”

Ice stability is a challenge. During the freezeup or breakup seasons, ice is wind driven and, depending on velocity, can go five to 10 miles a day. “A spill that’s incorporated in that ice, is obviously going to go with it,” said Glover. Shifting winds require spill responders to be able to change strategies and tactics on a daily basis.

Spring overflow happens when river ice breaks up before the near shore ice; and over a period of several weeks, millions of gallons of fresh water flow on to the ice. Glover likened the phenomenon to a tumbler with an ice cube in the bottom that has been frozen. A short time after filling the tumbler with water, the ice cube will dislodge and float to the surface. The phenomenon results in thick ice off shore capable of holding heavy equipment, while the near shore area will be in break up.

Remaining effective as an oil spill responder requires continued involvement in research and development, cooperative planning and response, and alternative technologies. “Thanks to our owners: ARCO, BP, Exxon and Alyeska, we’ve been able to assemble a world-class oil spill response organization on the North Slope,” Glover said.

“That organization is supported by an equipment inventory that is second to none anywhere in the world. But,” he said, “we cannot rely solely on mechanical containment and recovery to be effective on oil spills in the Arctic.” The present response planning standard that Alaska Clean Seas is held to relies solely on mechanical containment and recovery. Glover said he believes methods like in situ burning and surveillance and monitoring should be included in spill response plans.

What’s the end result? “What we like to do at the end of the day, every day,” Glover said, “is to be able go home knowing that we’ve done the very best that we possibly could to leave the North Slope in the same condition that we found it.”

Seasonal benefits, limitations

Tom Hall

The trickiest seasons for responders are the freezeup and breakup periods when the ice isn’t solid enough to support the weight of heavy equipment, but thick enough to prevent the use of boats. If necessary, they can use helicopters to drop gelled gasoline on a slick and burn it in place. “Tests that we have done prove that you can get 90 to 95 percent efficiency,” Glover said, “and leave about a 10 percent residue of the original volume.”

The residue, a taffy-like substance, can be retrieved later. When response is not possible, managers employ a variety of surveillance and monitoring techniques. Aerial reconnaissance with helicopters and fixed wing aircraft, satellite tracking, and GPS allow responders to monitor the migration of an oil slick. Relatively new, the forward looking infrared system is a device permanently mounted on an aircraft that can detect a temperature difference of one-tenth of a degree Fahrenheit even at speeds in excess of 100 miles per hour. It transmits an infrared image directly to the command center so real-time response managers can see what’s going on.

Despite the harsh conditions, the period from December to mid May virtually guarantees 100 percent clean up of an oil spill. By comparison, open water spill responders consider it a good day if they get 15 to 20 percent of a spill. In an Arctic environment, responders can even cut out an entire sheet of ice, haul it to land and recover the oil when the ice melts. “Nowhere else in the world do you have the advantages that this season offers,” said Glover.

Then comes spring. Deteriorating ice conditions, oil migrating to the surface and spring overflow limit site access and force on the spot decisions. “Can you afford to go out and physically pick this up and try to haul it back?” Glover asked. Or, do you “burn that oil in those melt pools leaving only 10 percent of its original volume for the polishing crews to go clean up?” Glover’s conclusion was, “You do the best that you can.”