The BP Whiting refinery in East Chicago, Ind., stands on Sept. 21, 2017. (DroneBase via AP, File)

The 134-year-old refinery, located between Hammond, Indiana, and Chicago, is the biggest in the U.S. Midwest and sixth largest nationally. It processes about 440,000 barrels of crude oil daily, making a variety of liquid fuels and asphalt.

Investigation Raises Questions About Oversight, More

The Indiana refinery responsible for the oil spill in Lake Michigan in March wasn't penalized by regulators. The Better Government Association raises questions about oversight and the safety of drinking water.

BP says all the oil  from last week's spill is now cleaned up. But activists worry about the possibility of future spills. Elizabeth Brackett has the latest details. View a graphic on the Lake Michigan oil spill compared to the 10 biggest U.S. oil spills by volume.