A 20,600 bbl Bakken crude oil spill in North Dakota from a leak sprung in a Tesoro Logistics LP pipeline in a wheat field northeast of Tioga, ND, on Friday was fully contained, under control and in the process of being remediated, according to state and company officials. The leak had originally been detected Sept. 29 and was mistakenly thought to be much smaller.

A unit of refiner Tesoro Corp. has indicated that the seepage first detected two weeks ago comes from a pinhole leak that may have been caused by corrosion. Tesoro said the affected pipeline segment has been temporarily shut down, the release stopped and repairs are under way.

The 20-year-old pipeline carries crude oil about 40 miles north of Tioga to Columbus, ND, where it is loaded on rail cars for shipment to various refineries. “There have been no injuries or known impacts to water, wildlife or the surrounding environment as a result of this incident,” which is calculated to be the largest since the Bakken Shale boom started in 2006, a company spokesperson said.

Located about a half-mile from the nearest farm, the spill area covers about 7.3 acres mostly underground and sits on the top of a hill with a thick clay layer about 12 feet below the surface, which is helping keep the oil contained, according to state officials. “There is no surface water or ground water impacted,” a spokesperson for the North Dakota Department of Public Health (NDDPH) told NGI’s Shale Daily on Friday.

“The company has stepped up to the plate and done everything that is desired at this site. They have contained, delineated it, and they are developing a remediation plan, so they are doing everything that needs to be done to correct the situation.”

With the help of a consultant, Tesoro is developing a remediation plan to clean up the spill, and it will be submitted to the NDDPH for state review during the next 10 days. The state, company and consulting firm’s representatives will meet to finalize the plan, the state NDDPH spokesperson said.

Along with the federal Pipeline and Hazardous Materials Safety Administration, Tesoro said it is working closely with the environmental health section at NDDPH. Kris Roberts, an environmental geologist at the state unit, credited Tesoro with being “aggressive in containing the crude oil.”