The attorney general of Illinois announced Thursday that the state is suing a U.S. subsidiary of Calgary-based Enbridge Inc., alleging the company violated environmental regulations in connection with a pipeline leak in Romeoville, near Chicago.

The Sept. 9 leak was the company's second of three in the United States in a period of less than three months.

Workers from Enbridge Energy Partners clean up an oil spill at an industrial park in Romeoville, Ill., on Sept. 13. (Michael R. Schmidt/Associated Press/The Beacon News)

About 970,000 litres of crude oil were released onto a roadway and then into a retention pond at an industrial park. U.S. federal officials said on Sept. 15 that more than 946,000 litres had been recovered.

The court also ordered Enbridge to inspect water mains, sanitary sewers and storm sewers, along with private wells and groundwater within half a mile of the leak, to assess the impact of the oil leak and ensure cleanup.

"Enbridge must be held accountable for all of the environmental and public health impacts of this oil spill," said Illinois Attorney General Lisa Madigan. The eight-count civil suit alleges Enbridge Energy Partners caused danger to public health and created a public nuisance.

An Enbridge spokeswoman said the company has worked co-operatively with authorities since Line 6A leaked. Enbridge has completed most of the actions the U.S. Environmental Protection Agency ordered it to take, and will soon finish the rest, Jennifer Varey added.

"By filing this action, the Illinois Attorney General's office is simply protecting the state's interests and ensuring that Enbridge will follow through with addressing any concerns that the state may have arising out of the Line 6A incident, in addition to those action items being addressed under the U.S. EPA Order," she said.

The suit seeks compensation for the costs incurred by the Illinois Environmental Protection Agency for its supervision of the cleanup. No estimate of the amount of compensation was released.

In the earlier spill, a break in an Enbridge pipeline in Michigan in July leaked 3.1 million litres of crude, some of it into a creek feeding the Kalamazoo River. The slick coated fish and Canada geese in oil. Enbridge estimated cleanup and other costs from that spill could reach $400 million US.

A third pipeline leak, near Buffalo, N.Y., in mid-September, resulted in negligible spillage.

With files from The Canadian Press