BRITTON, S.D. -- A TransCanada Corp. official says he believes an estimated 210,000-gallon oil leak discovered last week in South Dakota from the Keystone pipeline was a sudden and "immediate" event.

The American News reports that Erik Tatarchuk, a TransCanada vice-president, said at a Marshall County Commission meeting Tuesday that it is unlikely oil leaked long enough to soak into the soil.

TransCanada spokeswoman Jacquelynn Benson says the cause of the leak won't be known until further investigation.

Officials say TransCanada has about 165 people working on cleanup and assessment at the Marshall County leak site.

Tatarchuk says the section of pipeline that leaked was under about four feet of soil. The damaged pipe will be cut out and sent to the federal Pipeline and Hazardous Materials Safety Administration for analysis.