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BILLINGS, Mont. -- The cleanup of a major oil spill in the Yellowstone River has proven more difficult than expected and could go on for several more months, an Exxon Mobil Pipeline Co. executive said Thursday.
Areas hit hardest by the July spill should be cleaned up by the first half of October, the firm's vice president, Geoff Craft, said. That includes a 20-mile stretch of the Yellowstone from the spill site near Laurel downstream to Billings.
But scattered sites still would need to be dealt with, including contaminated river sections downstream of Billings and two large islands in the heavily affected area.
Work in those areas could continue until Thanksgiving, Mr. Craft said.
Slowing the cleanup effort has been the painstaking task of removing crude from hundreds of debris piles deposited by the same spring floodwaters that are widely believed to have triggered the 12-inch pipeline's failure.
The energy company did not want to bring in more workers than necessary to avoid trampling the riverbank, Mr. Craft said.
"Nobody would have guessed how hard it would be," he said. "We don't want to do more harm than good by bringing in too many people or too many vehicles. ... It's very labor intensive."
Within days of the 1,000-barrel spill, Exxon Mobil was ordered by the Environmental Protection Agency to complete its remediation work by Sept. 9. But officials said Thursday that date was not meant as a hard deadline.
EPA on-scene coordinator Craig Myers said the cleanup "is much more dictated by progress in the field instead of a date on the calendar."
Mr. Myers added that Montana officials would have to give final approval of Exxon Mobil's work.
About 1,000 people are involved in the effort to mop up the spill, including about 850 Exxon Mobil employees and contractors working along dozens of miles of riverbank.
Because the river was flooding when the pipeline failed, the spilled crude spread deep into the woods and across agricultural fields, making it hard in some cases to find and remove.
Despite the slow pace, state and federal regulators said significant progress has been made in the seven weeks since the spill.
Teams sent out to find oil are no longer reporting many significant pockets of pooled crude that can be recovered, Mr. Myers said. Instead, workers are concentrating on removing oil-stained vegetation and the debris piles.
The spill's remnants likely will linger long after crews are gone, said Sandi Olsen, head of the remediation division of the Montana Department of Environmental Quality.
But Ms. Olsen said any remaining deposits of oil were degrading and unlikely to pose a long-term threat.
So far, federal officials have completed reinspections on six river segments with oil contamination after Exxon Mobil said it had largely finished its cleanup in those areas. That's out of 167 contaminated segments, the EPA said.