PORTLAND – Durastone Inc. and its president pleaded guilty Tuesday to negligently discharging pollutants at its former plant in Portland.

James Duhamel, the concrete manufacturer’s owner and president, was sentenced in U.S. District Court to four years of probation for the misdemeanor. In addition to his probation, Duhamel also must pay a $2,500 fine.

Durastone must pay $19,705 in restitution to the Maine Hazardous Waste Fund and a $116,500 fine to the U.S. government.

The guilty plea comes nearly three years after investigators found that a company drainage pipe was leaking hydrochloric acid into a wetland adjacent to the Milliken Street business.

The city of Portland began receiving complaints in 1997 that the property was a mess and lacked storage space for storm water drainage and waste concrete.

In April 1999, federal and state investigators raided the company’s 12-acre site. They reported that a drainage pipe was leaking hydrochloric acid onto the ground near a stream.

Durastone cleaned up the property and closed its plant in January 2000. The closing came as a relief to residents of a nearby neighborhood, where the case had caused an uproar. In exchange for Durastone’s departure and cleanup, the city dropped its claim to a $200,000 bond the company had posted.

After tests showed the cleanup was complete, the state Department of Environmental Protection also dropped its claim to the bond.

In September 2000, Durastone filed for protection from creditors in U.S. Bankruptcy Court, citing cash flow problems largely due to the costs of environmental consultants and lawyers.