The Missouri Department of Natural Resources says crews are still working to clean up and identify the cause of an oil pipeline leak in suburban St. Louis.

Agency spokesman Brian Quinn said contractors for the pipeline company, TransCanada Corp., are assessing an excavated segment of the Keystone pipeline Wednesday to pinpoint the problem.

The leak was discovered last week near St. Charles.

The size of the oil leak hasn’t been determined, but the department estimates it was about 43 barrels, or 1,800 gallons (6,800 liters). It says the oil didn’t leak into any waterways.

Quinn says about 31 barrels of oil have been collected so far. He says crews have removed more than 1,000 cubic yards of soil.

The department is working to identify nearby wells for future groundwater testing.