MINNEAPOLIS (AP) — Enbridge Energy said it has stopped the flow of spilled artesian groundwater that began a year ago when workers installing the Line 3 oil pipeline in northwestern Minnesota punctured an aquifer.

The spill near Enbridge’s terminal in Clearbrook was one of the worst environmental accidents during construction of the 340-mile pipeline in Minnesota. Workers dug too deeply into the ground and the rupture resulted in a 24 million gallon groundwater leak.

The company told the state Department of Natural Resources that it stopped the uncontrolled leak on Tuesday. The DNR said it will monitor the repair and the investigation remains ongoing. The agency is looking at further restoration, mitigation and penalties.

The White Earth Band of Ojibwe and other pipeline opponents have been doing their own investigation, including drone footage, to check for further water impacts. They are calling for more accountability and details about the incident.

State regulators ordered Enbridge to pay $3.3 million and fix the damage. The company missed a deadline in October and paid an additional $40,000.

Line 3 starts in Alberta, Canada, and clips a corner of North Dakota before crossing Minnesota en route to Enbridge’s terminal in Superior, Wisconsin. The project was pronounced complete in September.