UPDATE 11:22 a.m

It might take weeks to determine how to fix a natural gas pipeline that ruptured beneath the Yellowstone River near Laurel Sunday, an official said Monday.

The 8-inch-diameter line, servicing Montana Dakota Utilities customers north of the Yellowstone River including those in Billings, burst Sunday afternoon around 1:40 p.m., shooting a geyser of natural gas upward from the river's surface. Emergency workers evacuated Riverside Park and other areas along the river to be safe. Highway 212 from Thiel Road to Interstate 90 was closed temporarily.

The line belongs to the Williston Basin Interstate Pipeline Company, an MDU Resources Group subsidiary. Spokesman Tim Rasmus-sen said the company doesn't know what caused the pipe to burst. Gas lines are buried several feet below water bodies for protection. Sunday's blast blew a section of the pipe to the river's surface.

"What we've got to do is investigate the procedure to remove the pipeline and evaluate the cause," Rasmussen said. "We want to assure the safety of our crew and the safety of the public."

The company isn't sure if the pipe beneath the river will need to be completely replaced or can be be repaired.

The 8-inch pipeline was actually a backup for a 16-inch natural gas line, Rasmussen said. But because of increasing demand in the Billings area, the smaller line was doing more than part-time work. Initial reports indicated the line served the CHS oil refinery in Laurel. The line served CHS, Rasmussen said, but the refinery wasn't its only customer.

Because of the 16-inch line's presence, natural gas service in the Billings area wasn't affected, Rasmussen said.

The rupture the subsequent gas release probably didn't affect Yellowstone River wildlife, according to Bob Gibson of the state Department of Fish, Wildlife and Parks. Natural gas bubbles into Montana rivers and streams ordinarily in other parts of the state, without harming trout.

The Williston Basin Interstate Pipeline system is a vast array of more than 3,200 miles of high pressure pipe servic-ing Montana, Wyoming and the Dakotas.

By ZACH BENOIT

Of The Gazette Staff

A broken gas line forced temporary evacuations and road closures Sunday near the Yellowstone River in Laurel.

Laurel Fire Chief Derek Yeager said a Williston Basin Interstate Pipeline Company natural gas line that runs through the Yellowstone River and into the CHS refinery broke around 1:40 p.m. When emergency responders arrived, they found that a 4- to 6-inch, large diameter high pressure gas line had ruptured and was free flowing into the river, shooting out of the water like a geyser and creating cloud fumes, Yeager said.

As a safety precaution, Riverside Park and other areas along the river were evacuated and Highway 212 from Interstate 90 to Thiel Road was closed.

The line was shut off and roads were reopened within an hour, Yeager said. The Montana Highway Patrol and crews from Montana-Dakota Utilities, Laurel fire and the refinery responded.

Yeager said natural gas leaks combined with atmospheric and weather conditions - cool and wet - found on Sunday can be especially dangerous, which is why the evacuations and closures were ordered. The gas can take on moisture and form clouds.

"It's really important because things like that are terribly subject to wind direction," he said. "It would have affected a lot of folks if the wind had been going another way. They form clouds and those clouds can travel for quite some time if the wind's right, and will either dissipate or find an ignition source, like a vehicle, and that's not good."

Lani Jordan, a CHS spokeswoman based at its corporate headquarters in St. Paul, Minn., confirmed that the line is one that runs into the refinery, but that the break was quickly under control. There are two natural gas lines running into the refinery, so it didn't affect operations, she said.