A farmer found crude bubbling out of the ground while harvesting wheat on his North Dakota farm on Sept. 29, apparently caused by one of the largest oil spills in the state, which is witnessing an oil boom.

The crude came from a rupture in Tesoro Corp's underground pipeline, and spread out to 7.3 acres or about the size of seven football fields, the Associated Press, or AP, reported, on the remote farm about nine miles north of Tioga in the northwestern corner of the state.

Farmer Steve Jensen said he smelled crude days before he found the tires of his combine coated with oil while harvesting his 1,800-acre farm. The oil was "like a faucet, 4 to 6 inches spewing out," Jensen told Reuters. "It was pretty ugly," he said adding that the crop "disintegrated, you wouldn't have known it was a wheat plant."

About 20,600 barrels of crude are expected to have leaked on to the farm, and according to Reuters, the release of oil has stopped and the spill has been contained. 

Tesoro, in a statement, said that containment and remediation could cost $4 million, but did not give any reason for the spill. 

And, while state authorities chose to make the spill public only 12 days after Jensen reported the incident, the spill did not contaminate ground water sources and posed no immediate danger to wildlife, according to Kris Roberts, who leads the environmental response team at the state's Department of Health, Reuters reported. Authorities also said that there were no lakes, streams or rivers within five miles of the spill. 

However, the leak has raised questions about the safety of water resources and safety measures practiced by the oil industry in the state. Gov. Jack Dalrymple said he was unaware of the spill until Wednesday, raising serious concerns about the practice of reporting oils spill in the state.

"Initially, it was felt that the spill was not overly large," Dalrymple said, according to AP. "When they realized it was a fairly sizable spill, they began to contact more people about it." He said that a probe has been launched on how oil companies report oil spills in the state.

In March, 20 houses were evacuated in Mayflower, Ark., when an Exxon Mobil pipeline spilled 5,000 to 7,000 barrels of crude into a lake and subdivision.