The former owner of a Youngstown-based wastewater company pleaded guilty Monday to federal Clean Water Act violations in the dumping of thousands of gallons of fracking wastewater into a northeast Ohio storm sewer.

Ben Lupo, 63, changed his earlier not guilty plea during a hearing before Judge Donald Nugent in federal court in Cleveland. He faces up to three years in prison, a year of supervised release and fines of up to $50,000 per day, to a maximum of $250,000. Sentencing is scheduled for June 16.

Authorities had charged that Lupo, of Poland, Ohio, ordered an employee at Hardrock Excavating LLC to repeatedly dump drilling mud and brine intended for deep injection into a sewer that empties into the Mahoning River watershed, or he dumped the material himself, between November 2012 and January 2013.

The employee, 34-year-old Michael Guesman of Cortland, was sentenced last week to 300 hours of community service and three years of probation.

U.S. Attorney Steven Dettelbach said he was pleased Lupo had admitted his actions and that Dettelbach's office would continue "to aggressively investigate and prosecute cases in which people pollute Ohio's waterways."

Randall Ashe, special agent in charge of the Environmental Protection Agency's criminal enforcement program in Ohio, said the case sends a signal to the state's growing energy industry.

"As natural gas exploration continues, it must be done in a way that ensures the drilling byproducts are treated and disposed of safely and legally," he said. "This case demonstrates that if companies and their owners skirt environmental laws, EPA will hold them accountable."

According to court documents, Hardrock's facility in Youngstown had about 58 mobile storage tanks holding a combined 20,000 gallons of waste, including oily mud and chemical-laced brine. Lupo directed an employee to empty some of the liquid waste into a nearby drain after everyone else had left the facility and after dark, the papers said.

A sample of the discharge collected Jan. 31, 2013 — the last night the dumping occurred — was black in color and contained several hazardous pollutants, including benzene and toluene.

Ohio Attorney General Mike DeWine said Lupo "put his own business interests ahead of the health and safety of our citizens, natural resources and wildlife."

"He will now be held accountable for this terrible crime," he said.

A message left Monday with Lupo's attorney, Joseph Gardner, seeking comment wasn't immediately returned.

The case remains under investigation.