Mayor Rahm Emanuel on Wednesday followed through on his threat to hold U.S. Steel responsible for two toxic spills into a waterway that feeds into Lake Michigan with the potential to endanger Chicago’s drinking water.

“We will not stand idly by as U.S. Steel repeatedly disregards and violates federal laws and puts our greatest natural resource at risk,” the mayor was quoted as saying in a press release.

In a lawsuit filed in federal court, the city accused U.S. Steel of violating the Clean Water Act by allowing the discharge of nearly 300 pounds of “carcinogenic” hexavalent chromium into the lake last spring and failing to notify downstream users of the impacted waters.

The pollutants were discharged into Burns Waterway – described as a “small industrial ditch” that empties directly into Lake Michigan – after a pipe broke and a collection trough corroded at the U.S. Steel plant in Portage, Indiana.

The lawsuit also cited U.S. Steel’s handling of an Oct. 25 spill that released 56.7 pounds of chromium after a wastewater treatment system malfunction. That second spill nearly doubled the 30 pounds of potentially cancer-causing chemical over 24 hours that the plant is permitted to release, the city said.

A third-party contractor working for U.S. Steel observed a “blue discharge with visible solids,” the lawsuit contends, but the company did not test to determine how much of the discharge was “the more toxic hexavalent chromium.”

It took the Indiana Department of Environmental Management three weeks to conduct an accident inspection of the second spill, the city contends.

City Hall learned of the second spill, only after a newspaper article was published and was never notified by U.S. Steel or any other regulatory agency, according to the lawsuit.

Emanuel argued that U.S. Steel’s secrecy prevented the city from protecting public health and taking “effective actions to avoid having the city’s water intake and distribution system contaminated.”

“Chicagoans rely on Lake Michigan for our drinking water, as an economic engine and as a recreational asset. This Great Lake is our most precious natural resource and we must preserve and protect it, while taking steps to punish those who pollute it,” Emanuel was quoted as saying.

Corporation Counsel Ed Siskel said he filed the lawsuit to “protect Chicago residents and the more than 5 million Illinois residents who rely on Lake Michigan as their source of drinking water.”

“After multiple spills in 2017, we do not believe that U.S. Steel is acting responsibly and in compliance with the Clean Water Act,” Siskel was quoted as saying.

The city’s lawsuit seeks injunctive relief and civil penalties against U.S. Steel for violating both the Clean Water Act and National Pollutant Discharge Elimination System permits issued to the steel giant.

U.S. Steel spokesperson Meghan Cox responded to the city’s lawsuit by arguing that the company has “worked cooperatively with government and regulatory entities to swiftly correct the issues” at its Midwest Plant in Portage, Indiana.

“We believe that protecting our water resources is of critical importance and have taken multiple steps to improve our environmental performance company-wide,” Cox wrote in an email to the Sun-Times.

After announcing his intention to sue U.S. Steel in late November, Emanuel accused federal environmental regulators of being “asleep at the switch” under President Donald Trump and “protecting the polluters.”

“I don’t think it’s an accident that U.S. Steel didn’t report it to the Trump EPA. They know exactly the attitude of the EPA under Donald Trump is that they can get away with it, they’re not going to be policed, they’re complicit in this pollution,” Emanuel said on that day.

“To the EPA under Donald Trump, this is a wake-up call: Don’t be sending your flimflam stuff and a slap on the wrist to them back here. It’s unacceptable. Everyone will be watching you.”