The Wisconsin Department of Natural Resources sent a letter to General Motors informing the automaker it has to clean a contaminated section of the Rock River.

The DNR sent the letter to GM Thursday. In part, the letter said GM is “responsible for investigating and restoring the environment” in an area of the river that’s near the automaker's former plant.

Polycyclic aromatic hydrocarbons (PAHs), metals and semi-volatile organic compounds (SVOCs) had been detected in sediment near the storm water outfall adjacent to the former GM facility.

GM spokesperson Dan Flores said the company is evaluating its next steps.

“We plan to perform some additional investigative work this month,” he said. “Then from there, we’re certainly committed to continue to cooperate with the city and with the Wisconsin DNR.”

A city report in January found contaminants during a routine sediment analysis. GM then did its own tests and the results were consistent with the city’s findings.

Janesville city leaders, GM and the DNR had several meetings throughout the year. With all the discussion, GM said it wasn’t a surprise to receive the letter.

In the letter, the DNR gives GM a few deadlines. It says the company must have written proof that it has hired an environmental consultant within 30 days or “the DNR may initiate enforcement action.” The letter says GM must also submit a work plan for completing its investigations within 60 days. However, the city said it’s hard to tell when the river will actually be cleaned.

“I don’t think we really know at this point how long this is going to take because GM has to do more investigative work,” Janesville Public Works Director Paul Woodard said.

GM said the cleaning process would not get in the way of selling the plant.

“We continue to remediate the facility and are continuing to work with potential developers to sell the property and ultimately return it back to productive use,” Flores said.

While Janesville will continue to work with the DNR and GM, the city said it’s not the one in charge.

“So while we’re a partner, we’re not a major player in this,” Woodard said. “It’s more the DNR’s responsibility to ensure GM is going to do the work necessary to clean up the river.”

The DNR has said the contamination isn’t harmful to the community through fish consumption or direct contact with the water.