Montana officials declared that the town of Glendive's water supply was safe for drinking again on Friday, after tests showed a drop in concentrations of carcinogenic benzene. The water had been contaminated by oil from a breached pipeline over the weekend.

“The water treatment plant is providing clean water,” reads a notice on the Glendive’s website. “Confirmation sampling of the distribution lines shows that the water meets federal drinking water standards. The final step is for residents and businesses to do any final flushing of their systems.

The contamination is linked to last Saturday's spill into the Yellowstone River of an estimated 1,200 barrels of crude oil from the Poplar pipeline, which ruptured several miles upstream of Glendive, in northeastern Montana.

The U.S. Environmental Protection Agency found earlier this week that the drinking water for some 6,000 people in and around the town contained benzene, an organic compound in oil and gas, at higher-than-acceptable levels. Benzene can cause leukemia, according to the American Cancer Society.

The spill happened close to Williston, North Dakota, a shale-oil boom town. Authorities there are monitoring their water for signs of benzene contamination, as the spill has affected a river, the Yellowstone, which flows into the Missouri river, from which Williston draws its water supply.

Bridger Pipeline LLC, the oil company behind the pipeline, has trucked tens of thousands of gallons of bottled water to Glendive after water sampling earlier this week showed elevated levels of benzene. It is unclear what caused the pipeline to break.

Responders have so far recovered about 246 barrels of petroleum from the breached pipeline, but cleanup efforts in the river have been hampered by the pooling of oil below thick layers of ice.

The Poplar pipeline carries 42,000 barrels of crude a day gathered from producers in eastern Montana and North Dakota.

Glendive water users were instructed Thursday evening on how to flush their taps of residual contamination in water lines, Bridger spokesman Bill Salvin said, adding that the company is prepared to continue to distribute bottled water to residents if necessary.

Al Jazeera and Reuters