Jerry Leggatte USBR/Flickr

It's been almost three weeks since

an ExxonMobil pipeline burst beneath the Yellowstone River in Montana, spilling an estimated 1000 barrels (42,000 gallons) of crude oil into the water. And still, cleanup crews keep coming. As of Monday, about 700 workers and regulators from ExxonMobil, the Environmental Protection Agency (EPA), state agencies and private spill-response companies were on the scene.

The Exxon spill in the Yellowstone River happened little more than a year after the BP oil disaster in the Gulf of Mexico. But oil spilled in a river is a very different beast than oil spilled at sea, Steve Merritt, the EPA's on-scene coordinator at the Yellowstone, tells PM. Here are the unique challenges of cleaning up the 300-mile (and counting) oil-dotted stretch of the river.

It's (Relatively) Easy to Stop a River Leak

Shutting off the leak is job one when responding to a spill, Merritt says, and in that respect Yellowstone responders had an easier task than the people trying to close off BP's Macondo well. It took BP multiple attempts with an armada of drill ships, capping equipment and van-size underwater robots to seal off the well. But the source of the Yellowstone spill was close to the surface. The 12-inch pipeline, which carries crude from oilfields in northern Wyoming to an Exxon refinery in Billings, Mont., is buried about 5 feet below the riverbed, according to the company.

Crews from ExxonMobil took about 10 minutes to find the spill and about 5 more minutes to turn off the pumps. Shortly thereafter they shut off valves on both banks of the river, preventing more oil from entering the section of pipe between the valves. Where BP spent three months trying to cap the leak in the Gulf, Exxon had the Yellowstone leak stopped within about an hour.

Still, there was plenty more to do. This past weekend, following recommendations from the Department of Transportation and the EPA, Exxon crewmen hooked up a vacuum truck to the buried line on either side of the break and sucked out another 18,900 gallons (about 450 barrels) of oily water. "We were concerned about a second discharge," Merritt says. "From my perspective, I don't want to risk more flooding and more potential damage to the pipeline."

But Corralling Oil in a Fast and Flooding River is Dangerous

For four days after the pipe burst, snow melting in Yellowstone National Park about 150 miles upstream from the spill raised the water level to near-record levels. It gushed past the busted pipe, carrying the oil downstream nearly to the North Dakota border and depositing some of it on the grassy, tree-lined riverbanks, in roadside ditches and in farmer's fields along the way. "The amount of force a river can have amazes me," Merritt continues. "That's a huge difference from a coastal zone spill, where you can get some wave action but it's fairly gentle."

Bob Rogers, the president of Bob Rogers and Associates, an environmental consulting company in Mississippi, says that if the river were at normal height (and didn't have cottonwoods in the middle of it), cleanup crews would most likely have strung floating snake-like booms from bank to bank to corral oil. With booms in place, responders could have begun to use skimmers to separate the oil from the water, similar to what happened in the Gulf last year. Finally, they would have sucked up the oil with vacuum trucks, burnt it or soaked it up using sheets of oil-loving solvents.

But not this time. Currents faster than 1 knot would snap the ropes tethering a containment boom, Merritt says. At the height of the spill in the Yellowstone, the river was running at about 7 to 10 knots. "There just isn't technology to fight a river like that," he says.

Unable to access the main channel of the Yellowstone, orange-vested cleanup workers went low-tech, spending most of their time wiping oil off grasses and trees with absorbent pads. They were able to lay some booms in side channels and soak it up with the pads. As of last Friday, they'd used up some 260,000 pads and over 50,000 feet of booms. "It's not rocket science," Merritt says. "Most of what we're doing is picking up the oil, putting it in bags and disposing of it."

Chemical Dispersants Aren't an Option

The one thing cleanup crews on the Yellowstone wouldn't even consider using to clean up the spill, flood or no flood, is a chemical dispersant.

"Dispersants are a big-ticket item in the sea," Rogers says. They are often used, as during the BP spill, to get rid of oil on the ocean surface in places where it can't be removed with booms and skimmers or by controlled burning, such as in rough seas far from shore. When sprinkled on a slick, dispersants help break it down into smaller droplets that either rise back to the surface or, in most cases, drift down into the water column where ocean microbes break them down.

In a river, however, spill responders generally agree that dispersants create more problems than they solve. "I don't know of any case where chemical dispersants were used in a river," says Robert Simmons, president of Environmental Science Services in Louisiana. Because rivers are so much shallower than the sea, responders worry that sinking droplets of oil might settle in the gravel and sediment of a riverbed rather than stay suspended in the water column. Once dispersed along the river bottom, the oil might persist in the river much longer than if responders simply let it wash downstream.

The Work Goes On

Investigators at the Pipeline and Hazardous Materials Safety Administration say it could take months to figure out what caused the pipe to rupture, though there's been some speculation that recent flooding and fast-flowing debris may have had something to do with it.

Merritt says that cleanup crews have captured just nine of the 1000 barrels spilled. He doesn't expect them to capture much more. Some of the oil will be left to decompose naturally in places along the river where Yellowstone County officials worry that cleanup crews might disturb delicate ecosystems or spread noxious weeds. The rest will be slowly and meticulously wiped off grasses, logs and trees. Merritt estimates it will take a crew of several hundred workers two or three months of "methodical and physical effort" to sufficiently clean up the spill. "Unfortunately, you can't go out there and spray it all off," he says.

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