Federal prosecutors have filed criminal charges against ExxonMobil for a diesel spill in Boston Harbour.
Under a plea agreement, the US oil company will pay $6.1m in fines and community service payments.
The US Department of Justice said Monday that the oil company is accused of violating the Clean Water Act in connection with a January 2006 spill of 47.8 tonnes of diesel oil.
The incident occurred at ExxonMobil's oil products terminal in Everett, Massachusetts.
"ExxonMobil takes its environmental responsibility very seriously," the company said in a statement. "We very much regret that in January of 2006, we had a release of a petroleum product into the Island End River in the Boston area which resulted in a misdemeanor violation of the Clean Water Act."
According to an information filed by prosecutors, the 47,200-dwt products tanker Nara (built 2006) was unloading low-sulphur diesel fuel at the terminal's Berth 3. But a seal valve suffering from wear and tear leaked oil into the product receipt line from Berth 1.
The leak built pressure in the Berth 1 line until it burst, spilling fuel into the river.
Prosecutors say ExxonMobil had been aware of the faulty valve since September 2005.
"ExxonMobil's negligent failure to provide adequate resources and oversight to the maintenance and operation of the Everett terminal was a direct cause of the spill," the Justice Department said.
ExxonMobil Pipeline Co, which operates the terminal, has agreed in the plea deal to have court-appointed observer monitor the facility.
The company's $5.64m community service payment will go to a fund of the North American Wetlands Conservation Act.
A federal judge must sign off on the plea agreement.
Irving, Texas-based ExxonMobil did not immediately respond to a request for comment.