None of them were reported to the public, officials said.
According to records obtained by The Associated Press, the pipeline spills, many of them small, are among some 750 "oil field incidents" that have occurred since January 2012 without public notification.
"That's news to us," said Don Morrison, director of the Dakota Resource Council, an environmental-minded landowner group with more than 700 members in North Dakota.
Dennis Fewless, director of water quality for the state Health Department, said regulators are reviewing the state's policies for when to publicly report such incidents after a massive spill was discovered last month in northwestern north Dakota by a wheat farmer.
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North Dakota regulators, like in many other oil-producing states, are not obliged to tell the public about oil spills under state law. But in a state that's producing a million barrels a day and saw nearly 2,500 miles (4,000 kilometers) of new pipelines last year, many believe the risk of spills will increase, posing a bigger threat to farmland and water.
"We're certainly looking at that now and what would be a threshold for reporting to the public," Fewless said. Taking notice of the recent criticism, the state issued a statement Oct .17 on an estimated 7-barrel oil spill in Divide County, which borders Canada in far northwestern North Dakota.
"We really have to dig through our data base to get specifics," said Fewless, adding that a more user-friendly tracking system for regulators may be developed.
Such a system would be valuable for the public, too, said Louis Kuster, who raises wheat near Stanley in northwest North Dakota. Farmers and ranchers rely on land for their livelihood, so information on spills that could threaten land or water supplies "absolutely is important for us to know," he said.