A quarter-mile segment of the 12-inch pipeline was replaced by drilling a new passage an estimated 60 to 70 feet beneath the riverbed. That change makes it far less likely that the Silvertip pipeline will fail a second time, Montana Department of Environmental Quality Director Richard Opper said.
"There were a lot of eyes on this from our federal partners," Opper said of repairs to the line. "It was done right. It's a lot safer pipeline now, at least crossing the river."
The 20-year-old line broke near Laurel on July 1 after flooding scoured the river bottom and exposed the pipe, which had been buried just five feet deep in some areas. Released oil fouled dozens of miles of riverbank, contaminated crops and pastureland and was blamed for killing birds, reptiles and other wildlife.
Although relatively small compared to other spills, the Yellowstone accident drew widespread attention because it followed a recent string of pipeline failures across the country and occurred along a waterway renowned for its fishing and scenery.
An investigation is pending into whether Exxon Mobil violated safety rules prior to the accident. Officials in Laurel had notified both the company and federal regulators that they were worried about a potential failure of the line due to erosion.
Federal pipeline safety officials said they had conducted an extensive review of the repairs made by Exxon Mobil to ensure the line could be operated in a safe and environmentally sound manner.
The flow of oil will resume once integrity checks have been completed on the line, company spokeswoman Rachael Moore said. She declined to say when that would be, but Opper said he was told Saturday.
The federal Pipeline and Hazardous Materials and Safety Administration said in a Friday statement that its inspectors would be on hand for the restart.
Federal regulators also required that two more of the pipeline's river crossings be replaced, at Rock Creek and the Clarks Fork of the Yellowstone. That came after safety officials required Exxon Mobil to re-evaluate the crossings in the wake of the Yellowstone spill.
The work on the two crossings is to be completed by next March, Moore said.
"Prior to completion of the new crossings, (Exxon Mobil) will monitor daily stream flow conditions and institute shut down and isolation procedures if flow conditions exceed agreed upon thresholds," Moore said in an emailed statement.
The cleanup of remaining oil along the Yellowstone continues. At its peak more than 1,000 Exxon Mobil contractors were involved in removing contaminated vegetation and mopping up pockets of crude.
Only about 10 barrels of crude oil, or 420 gallons, were recovered, according to federal officials. Exxon Mobil and the DEQ are negotiating terms of the remaining work.
Silvertip is the main crude source for Exxon Mobil's 60,000-barrel a day refinery in Billings. The company had to scale back refinery operations and scramble to find other sources of oil while the line was down.
Local officials had worried jobs could be lost from the refinery if the pipeline repairs took too long. Yellowstone County Commissioner on Friday welcomed news that the line would soon start up again.
He said the refinery provides work for 380 Exxon Mobil employees and contractors.
"What this means is it's keeping people working and it means Exxon can contract out work. It's keeping people in jobs and dollars flowing in the community," Kennedy said.
The company in July estimated its response to the spill could cost more than $42 million. That was only a preliminary figure, and final costs could be higher after the cleanup proved more difficult than first expected.
The cause of the pipeline's failure remains under investigation.
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