CLEVELAND: One of the men at the center of an investigation into the illegal dumping of drilling wastewater in Youngstown pleaded guilty Thursday, days after his former employer lost a fight to keep its state operating permits.

The worker, Michael P. Guesman, admitted to illegally dumping brine and oil-based drilling mud into a sewer that empties into the Mahoning River watershed, the U.S. attorney in Cleveland, Steven Dettelbach, said.

Guesman, 34, of Cortland, changed his earlier plea of not guilty to a charge in a federal indictment against him, a Youngstown business and its owner.

Authorities allege the owner of Hardrock Excavating LLC, Ben Lupo, directed Guesman to discharge thousands of gallons of drilling mud and brine into a sewer that empties into the Mahoning River watershed from December to January, a violation of the Clean Water Act. Such drilling wastewater is supposed to be placed in an underground well piped deep into the earth.

Guesman’s attorney did not return a request for comment Thursday. He was scheduled to be sentenced in November.

Lupo has pleaded not guilty to the Clean Water Act violation.

The Ohio Department of Natural Resources revoked the permits of Hardrock and D&L Energy, which was formerly headed by Lupo, after workers at the companies’ Youngstown headquarters reported seeing the material being dumped.

Last week, an independent review board upheld the order revoking the permits of D&L.

Charges brought against Guesman and the 62-year-old Lupo, of Poland, carry penalties of up to three years in prison, a $250,000 fine and a year of supervised release.