ST. LOUIS (AP) — An oil leak near St. Louis prompted the closure of parts of two pipelines as crews work to determine the source, company officials and Missouri regulators said Thursday.

The leak was discovered Wednesday near St. Charles, Missouri, about 30 miles (48 kilometers) northwest of St. Louis. TransCanada Corp.’s Keystone pipeline and Enbridge Inc.’s Platte pipeline are among several that run through the area. Crews on Thursday were preparing excavation work to figure out where the leak originated.

“The source of the release has not been fully determined, but it is apparent that it originated at either the TransCanada Keystone pipeline or the Enbridge pipeline; there is no visible release near the other pipelines,” Missouri Department of Natural Resources spokesman Brian Quinn said in an email.

TransCanada spokesman Terry Cunha said in a statement that the Keystone pipeline was closed from Steele City, Nebraska, to Patoka, Illinois. Enbridge’s Platte pipeline was initially closed from Casper, Wyoming, to Wood River, Illinois. By Thursday, only the section from Salisbury, Missouri, to Wood River remained closed, a company spokesman said in an email. Both companies are based in Canada and have cleanup crews at the site.

Officials don’t yet know how much oil leaked, but the DNR’s preliminary estimate is 43 barrels, or 1,800 gallons (6,814 liters). Quinn said the spill was contained to an area of about 4,000 square feet (372 square meters), and did not reach any waterways, including the Mississippi River, which is about 2,000 feet (610 meters) away.

A St. Charles County spokeswoman said there did not appear to be any evacuations since the area near the leak is not heavily populated.

The 30-inch (76-centimeter) diameter Keystone line and the 20-inch (51-centimeter) diameter Enbridge line are both buried about 8 feet (2.4 meters) below the surface, Quinn said.

Shares of TransCanada and Enbridge both dropped about 1 percent.