BILLINGS — A Wyoming company said Friday it will replace a pipeline that spilled almost 40,000 gallons of oil into a river in Montana with a new line buried more deeply to protect against future accidents.

The Jan. 17 spill into the Yellowstone River contaminated the water supply for 6,000 residents of Glendive in eastern Montana. The city’s water was certified safe to drink on Friday after tests showed it no longer had harmful levels of benzene, a cancer-causing component of crude.

The cause of the spill remains under investigation. 

The Poplar Pipeline will stay shut down from Glendive to near the Canada border until the damaged section is replaced, said Bill Salvin, spokesman for owner Bridger Pipeline LLC.

The 340-mile line delivers crude from the Bakken oil patch of North Dakota and Montana to a terminal in Baker, Montana, about 55 miles south of Glendive. It was built in the 1950s and has a capacity of 42,000 barrels of oil a day. 

The southern section of the line remains operational.

When it was first installed, workers dredged the river and laid the pipe across the bottom.

A 2012 inspection determined the line was buried at least 8 feet beneath the riverbed, according to Bridger Pipeline. In August of that year, federal regulators told Montana authorities that the line had “adequate cover.”

But prior accidents, including a 2011 Exxon Mobil pipeline spill on the Yellowstone near Billings, have demonstrated that pipelines beneath bodies of water can quickly become exposed by floodwaters or other natural forces. 

Officials haven’t been able to say if the Poplar line was similarly exposed. Much of the Yellowstone is covered with thick ice that prevents direct access to the line and has complicated cleanup efforts.

One factor investigators will consider is whether a massive ice jam in early 2014, which local residents say blocked the Yellowstone near the site of the pipeline breach, could have previously damaged the line.

To install its new section of pipeline, Bridger Pipeline would use a technique known as directional drilling — a process in which lines are drilled sometimes dozens of feet beneath a river through solid rock or other material considered more stable than the constantly shifting riverbed.

The timing and cost of replacing the river crossing was not yet known. 

Cleanup crews on Thursday recovered another 34 barrels of oil from the damaged section of line. That’s equivalent to about 1,400 gallons and reduces the amount believed to have entered the Yellowstone to roughly 39,000 gallons, Salvin said.

Bridger Pipeline is a subsidiary of True Cos.

A sister company operating in Wyoming, Belle Fourche Pipeline, had three oil spills within a month in 2014 totaling more than 100,000 gallons of crude. Those spills included a malfunction that caused an oil storage tank to overflow and spill 70,000 gallons, a 25,000-gallon spill from a corroded section of pipeline, and a 9,000 gallon spill when heavy equipment damaged one of the company’s pipelines.