By Nia Williams
Nov 20 (Reuters) - Canada Corp TRP.TO has started initial excavation work at the site of an oil spill on its Keystone pipeline in South Dakota but has not yet pinpointed where the leak came from, a state official said on Monday.
The 590,000 barrel per day Keystone pipeline, which links Alberta's oil sands to U.S. refineries, was shut down on Thursday after a 5,000 barrel spill. TransCanada is working through the clean-up process, said Brian Walsh, environmental scientist manager for the South Dakota Department of Environment and Natural Resources.
"They are digging some smaller excavations to get a sense of where the oil is and have started recovering oil from this area," Walsh said.
TransCanada spokesman Terry Cunha said it had around 150 people on site working around the clock and the cause of the leak was under investigation.
The company has not yet set an expected restart date for Keystone, which is one of Canada's main crude export pipelines.
Canadian heavy crude grades remained under pressure on concerns about crude getting bottlenecked in Alberta. Western Canada Select heavy blend crude for December delivery in Hardisty, Alberta, settled at $16.25 per barrel below benchmark U.S. crude, according to Shorcan Energy brokers.