TransCanada last week notified the U.S. Pipeline and Hazardous Material Safety Administration that it closed the Keystone oil pipeline for repairs after was what described as an anomaly in a section of the pipeline running from Missouri to Illinois.
The pipeline was scheduled for a weekend restart, though TransCanada spokesman James Millar said in a statement that "wet weather played quite a factor (in the restart) as it was difficult getting heavy excavation equipment on site."
The company provided few details about the specific location of the excavation but said no leak occurred on the line.
The Keystone pipeline runs 2,100 miles from oil fields in Alberta province to refineries in Illinois and Oklahoma. It transports about 500,000 barrels of so-called tar sands oil per day.
Millar said the pipeline would operate at a slightly reduced pressure for about a day while the company conducts further testing.
"Once the pipeline system is operating at full pressure, we will be curtailing October volumes and will return to contractual delivery levels in November," he said. "We will be having direct discussions with our customers regarding the impact this will have on their deliveries to us."