When pipeline rupture sent more than 20,000 barrels of crude splashing across a North Dakota farmer’s wheat field, it took nearly two weeks before state officials told the public about it. Though the spill was in a remote area and didn’t contaminate water or hurt wildlife, environmentalists say the quiet way the state handled it is the latest example of a boom industry operating with all-too-casual oversight by timid regulators.

The find on Sept. 29 turned out to be one of the largest spills recorded in the state. At 20,600 barrels it was four times the size of a pipeline rupture in late March that forced the evacuation of more than 20 homes in Arkansas.

When North Dakota farmer Steve Jensen discovered oil “spewing and bubbling 6 inches high” from a hole in Tesoro Corp.’s underground pipeline, the spill was already the size of seven football fields.

But it was 12 days after Jensen reported the spill before state officials told the public what had happened, raising questions about how North Dakota, which is in the midst of an oil boom, reports such incidents.

The spill happened in a remote area in the northwest corner of the state. The nearest home is a half-mile away, and Tesoro says no water sources were contaminated, no wildlife was hurt and no one was injured.

The release of oil has been stopped. “It is completely contained and under control,” said state environment geologist Kris Roberts. “They got very lucky.”

The rupture in the 20-year-old pipeline may have been caused by corrosion.

Eric Haugstad, Tesoro’s director of contingency planning and emergency response, said the hole was a quarter-inch in diameter. Tesoro officials were investigating what caused the hole in the 6-inch-diameter steel pipeline that runs underground about 35 miles from Tioga to a rail facility outside of Columbus, near the Canadian border. The company estimated the cleanup would cost $4 million.

Gov. Jack Dalrymple, who says he wasn’t even told about what happened until Wednesday night, said the state is now investigating its procedures for reporting spills.

“There are many questions to be answered on how it occurred and how it was detected and if there was anything that could have been done that could have made a difference,” Dalrymple said Thursday, when questioned at a news conference on a separate topic.

“Initially, it was felt that the spill was not overly large,” Dalrymple said. “When they realized it was a fairly sizable spill, they began to contact more people about it.”

Jensen said he had harvested most of his wheat before the spill, but the land is no longer usable for planting.

“We expect not to be able to farm that ground for several years,” he said.

Tesoro Logistics, a subsidiary of the San Antonio-based company that owns and operates parts of Tesoro’s oil infrastructure, said in a statement that the affected portion of the pipeline has been shut down.

“Protection and care of the environment are fundamental to our core values, and we deeply regret any impact to the landowner,” Tesoro CEO Greg Goff said in a statement. “We will continue to work tirelessly to fully re-mediate the release area.”

Wayde Schafer, a North Dakota spokesman for the Sierra Club, said the spill is an example of the lack of oversight in a state that has exploded with oil development in recent years.

“We need more inspectors and more transparency,” Schafer said. “Not only is the public not informed, but agencies don’t appear to be aware of what’s going on and that’s not good.”