One year after construction triggered a flood of spilled artesian groundwater, Enbridge Energy says it has pumped enough grout into the ground to seal the aquifer that crews punctured in northern Minnesota while building the Line 3 oil pipeline.

Enbridge told the state Department of Natural Resources (DNR) that it stopped the flow of groundwater at the site Jan. 18, according to a notice on the department's website. The DNR said it will monitor the repair to ensure it holds.

"In addition, the DNR continues to work on its ongoing investigation and a comprehensive enforcement resolution that will address restoration, mitigation, and additional penalties associated with Clearbrook as well as two other aquifer breaches," the department said in the posting.

The rupture was one of the worst environmental accidents during construction of the bitterly opposed 340-mile pipeline in Minnesota. There were 28 documented drilling mud spills and frac-outs, and state regulators are investigating two other aquifer breaches at undisclosed locations.

The White Earth Band of Ojibwe and other pipeline opponents are doing an independent investigation, including collecting drone footage, to check for further impact on water.

Last year's breach was made more alarming by the fact that neither the company nor independent monitors told state regulators until months after it happened. The rupture wasted huge volumes of groundwater, and the outflow endangered a rare calcareous fen, a protected wetland fed by groundwater.

The breach occurred near a large pipeline junction outside Clearbrook, Minn., in Clearwater County.

State regulators ordered Calgary, Alberta-based Enbridge to pay $3.3 million and fix the damage. The company missed a deadline in October and paid an additional $40,000. At that time, regulators estimated that at least 50 million gallons of groundwater had flowed out since the accident.

The state Attorney General's Office has been considering potential criminal charges in the matter.

The DNR said the repair took time because the problem was so complex.

"In this instance, the company's data collection, planning, repair and testing took from mid-June to mid-January," said DNR spokeswoman Gail Nosek. "The DNR carefully oversaw this work to ensure that repair efforts didn't inadvertently increase environmental impacts."

She said the regulator will hold Enbridge "fully accountable for damages to Minnesota's valued natural resources and violations of state law."

Enbridge did not answer specific questions, but spokeswoman Juli Kellner issued a statement saying the company is working with the DNR to monitor the repairs.

As for concerns about the frac-outs along the line, Kellner reiterated that drilling fluid, or mud, is not toxic and consists mostly of clay and water. It's common for the mud to rise to the surface during drilling, she said, and Enbridge always reacted appropriately to the spills, shutting down drilling when they happened and cleaning up the mud under state and third-party supervision.

"Cleanup was completed months ago during construction of the project," Kellner said.

Winona LaDuke, head of Honor the Earth and a leading voice in the fight against the pipeline, said she's skeptical of Enbridge's repair.

"They were not even transparent about having created the fiasco," LaDuke said. "If it's true that they stopped the leak with the thumb in the dike, that's great. We want it stopped. It took a year. You don't get a medal for that. We have no idea of the damage."

"What's the value of destroying an aquifer? How does that get set?"

LaDuke said she it's ironic that she is headed to court next week on trespassing charges after being arrested during Line 3 demonstrations.

"Where's Enbridge's charges? I'm not the criminal," LaDuke said. "I was defending the waters of Minnesota."

LaDuke was scheduled to speak Friday at a demonstration at the DNR's offices in St. Paul.

Others planned to gather at the site of the breach Friday for a prayer ceremony. Dawn Goodwin, a member of the White Earth Anishinaabe and co-founder of the RISE coalition, an indigenous group opposing Line 3, said the fix is a relief. But there should have been more oversight to prevent the accident from ever happening, she said.

She also said she's skeptical about the timing of Enbridge's repairs, just before the one-year mark.

"It [the water] ran for a year and lo and behold, unsurprisingly, it's fixed just when we made public our event," Goodwin said.

The ceremony will involve Bois Fort Band of Chippewa and White Earth tribal elders and drummers, Goodwin said. The aim is healing.

"We see it as our mother's vein being ruptured," Goodwin said. "We just want to make sure the process is fixed so it doesn't happen again."

Sara Wolff, advocacy director for the Minnesota Environmental Partnership, accused Enbridge of being deceptive to get the pipeline built quickly and of misrepresenting the risks of the horizontal drilling techniques it was using to cross beneath rivers and creeks.

"There are huge cavities of drilling sludge left underground near these waters," she said. "We're seeing it bubbling up still in these winter months. It has not been cleaned up."