04/07/2016 06:21 EDT | Updated 04/08/2017 01:12 EDT

Keystone pipeline down longer than expected as crews look for source of leak

CALGARY — TransCanada has informed its customers that the Keystone pipeline will remain closed until early next week rather than reopen by the end of this week as previously expected.

The Calgary-based company's crews have dug up some of the soil surrounding a segment of the pipeline in southeastern South Dakota, about 60 kilometres southwest of Sioux Falls, but the source of the leaked oil hasn't been pinpointed.

TransCanada spokesman Mark Cooper says the situation is evolving but it appears the problem is relatively small in scope and that there's no immediate evidence of a significant environmental impact.

Cooper says it's too soon to say how much oil escaped before the pipeline was shut down for repairs.

The Keystone pipeline — in service since 2010 — can handle 550,000 barrels per day and is a major route for Alberta crude on its way to refineries in Illinois and Oklahoma.

TransCanada was alerted to the problem on Saturday by a farmer and quickly shut down the pipe to prevent further spills.