The US Coast Guard and Environmental Protection Agency were called in to contain the spill after the oil was released from a tank owned by construction equipment manufacturer Caterpillar Inc in Rockdale, Illinois.

But despite their best efforts to keep the oil remained on land, several thousand gallons leaked into the Des Plaines River, forcing the Coast Guard to close it to vessels and enforce a safety zone in the area.

The spill occurred when an electric pump in the facility’s waste oil and water separation system failed, causing two waste oil collection pits about 100 feet from the river to overflow.

Most of the oil collected in a gravel parking area, but about 10% ran down an embankment into the river and traces of it were spotted three miles downstream.

A Coast Guard helicopter survey immediately after the incident showed no obvious signs of dead fish or other wildlife.

The Environmental Protection Agency (EPA) said it took two days to remove all of the oil from the area, and it has since been carrying out investigations into the impact of the spill.

An EPA spokesman told edie: “Visual surveys by EPA and partner agencies indicate the damage was minimal to ecosystems and wildlife.

“Spilled oil in the river that could not be collected eventually disbursed and was diluted.”

He said the agency was now reviewing Caterpillar’s Oil Spill Prevention Control and Countermeasures Plan, which is a legal requirement, and will decide whether any action should be taken against the firm.

“Regulatory consequences, if appropriate, will be announced at a later date,” he added.

Caterpillar was unavailable for comment.

Kate Martin

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