CALGARY — TransCanada has shut down its Keystone pipeline while it investigates an oil spill in South Dakota, the company said Monday.Mark Cooper, a spokesman for TransCanada, said a local landowner noticed signs of an oil spill around noon local time Saturday and informed the company.The pipeline, which carries about 500,000 barrels of oil a day, was shut down in minutes, Cooper said.TransCanada Corp to face just one Energy East injunctionTransCanada Corp upgraded as earnings to become less cyclical“As soon as we got that report in we immediately began efforts to shut down the pipeline and crews were immediately dispatched to the site,” Cooper said.He said it was difficult to determine precisely how much oil was spilled, though the company said it covered a “small surface area” with no significant impact to the environment observed. The company continues to investigate the source of the spill, he added.The spill was found about six kilometres from TransCanada’s Freeman pump station, which sits roughly 60 km southwest of Sioux Falls, S.D.The company said it has notified landowners and local agencies in the area as well as regulatory agencies including the National Response Center and the Pipeline and Hazardous Materials Safety Administration.The Keystone pipeline carries oil from Hardisty, Alta., east through to Manitoba before it turns south to markets in the American Midwest and U.S. Gulf Coast.TransCanada said it has notified customers that the pipeline running from Hardisty to Cushing, Okla., and to terminals in Illinois would remain shut until at least Friday, while the Gulf Coast extension of the pipeline remains active.The incident comes as TransCanada continues to push forward its proposed 4,600-kilometre Energy East Pipeline that would ship Alberta crude to New Brunswick.The company hit a major setback in its pipeline expansion plans when U.S. President Barack Obama rejected its proposed Keystone XL pipeline last November.Environmental groups had opposed the pipeline, which would have run from Hardisty to Nebraska, both because it would allow increased exports of oilsands crude and because of potential spills. read more