BILLINGS, Mont. (AP) -- A second large oil spill into Montana's Yellowstone River in less than four years is reviving questions about oversight of the nation's aging pipeline network.
Investigators and company officials on Wednesday were trying to determine the cause of the 40,000-gallon spill that contaminated downstream water supplies in the city of Glendive.
Sen. Jon Tester said Saturday's spill from the decades-old Poplar Pipeline was avoidable, but 'we just didn't have the folks on the ground' to prevent it.
The Montana Democrat told The Associated Press that more frequent inspections by regulators are needed, and older pipelines should face stricter safety standards.
'We need to take a look at some of these pipelines that have been in the ground for half a century and say, 'Are they still doing a good job?' ' Tester said.
The latest spill comes as Republicans and some Democrats, including Tester, want the Obama administration to approve TransCanada's Keystone XL pipeline from Canada to the Gulf.
Keystone would cross the Yellowstone roughly 20 miles upstream of the Poplar Pipeline spill.
In 2011, an ExxonMobil pipeline break spilled 63,000 gallons of oil during flooding on the Yellowstone near Billings. The break was blamed on scouring of the river bottom that exposed the company's Silvertip line to floodwaters.
Officials involved in the Poplar Pipeline spill have said it's too soon to say if that line also was exposed.
Poplar, owned by Wyoming-based Bridger Pipeline, was constructed in the 1950s. The breached section beneath the Yellowstone was replaced at least four decades ago, in the late 1960s or early 1970s, according to the company.
Based on the number of miles of pipelines in the U.S. that carry oil, gasoline and other hazardous liquids, just over half were installed prior to 1970, according to the U.S. Department of Transportation.
The agency's Office of Pipeline Safety has roughly 150 inspectors overseeing 2.6 million miles of gas, oil and other pipelines.
That number is slated to increase by another 100 inspectors under a $27 million budget increase approved last year. That would still leave inspectors stretched thin given the mileage of pipelines.
Dena Hoff, a farmer and rancher whose land borders the site of the Poplar accident, said she's had a good working relationship with Bridger Pipeline, and she commended the company for taking responsibility for the spill.
But Hoff said the spill should spur second thoughts about Keystone and whether it's a good idea to have pipelines that cross beneath surface waters.
'It's the nature of the beast. Pipelines leak and pipelines break. We're never going to get around that,' she said. 'We have to decide if water is more valuable than oil.'
Authorities continue work to clean up Glendive's public water supply after cancer-causing benzene was detected in water coming from the city's treatment plant. The plant draws directly from the Yellowstone.
Bridger Pipeline has committed to providing bottled water for Glendive's roughly 6,000 residents until the water-treatment plant is running again.
Late Wednesday night, Dawson County Disaster and Emergency Services Coordinator Mary Jo Gehnert said in an email that the plant has been decontaminated. If tests conducted Thursday show that the plant's water is safe to use, county workers will give information to the public on how to flush the water in homes and businesses, Gehnert said.
Workers late Tuesday recovered about 10,000 gallons of oil that was still in the Poplar line after it was shut down because of the breach.
Bridger Pipeline Co. spokesman Bill Salvin said Wednesday only a 'very small' amount of oil has been siphoned from the river itself.
Company officials and government regulators say most of the oil is thought to be within the first 6 miles of the spill site. That includes the stretch of the river through Glendive.
'What we're working on is identifying places where we can collect more oil,' Salvin said. 'The cleanup could extend for a while.'
Oil sheens have been reported as far away as Williston, North Dakota, below the Yellowstone's confluence with the Missouri River, officials said.
The farthest downstream that free-floating oil has been seen was at an intake dam about 28 miles from the spill site, officials said.
Montana Department of Environmental Quality Director Tom Livers said he was concerned that when the ice breaks up in the spring, oil will spread farther downstream.