The Minnesota Department of Natural Resources has ordered Enbridge to pay $3.32 million for failing to follow environmental laws during construction of its controversial Line 3 oil pipeline.

While working near Clearbrook, Minn., Enbridge dug too deeply into the ground and pierced an artesian aquifer, which the DNR described Thursday as an "unauthorized groundwater appropriation." The incident, which happened in January, has led to a 24 million gallon groundwater leak, endangering a nearby wetland.

"Enbridge's actions are a clear violation of state law, and also of the public trust," said Barb Naramore, DNR deputy commissioner. "That is why we are using all of the tools in our authority to address the situation."

The DNR has ordered Enbridge to put $2.75 million into escrow for restoration and damage to the delicate wetland, known as a calcareous fen. The DNR's enforcement orders require Enbridge to pay $300,000 to mitigate the lost groundwater and $250,000 for long-term monitoring of the wetlands.

The state also fined Enbridge $20,000, the maximum allowed under state law. Enbridge does not have to pay the fine if it fixes the problem in the time allotted. Enbridge could get some of the $2.75 million in escrow back if remediation costs less, or it could end up paying more if the bill is higher.

In a statement, Enbridge said it had "just received" the DNR's complaint and is reviewing it.

"Enbridge has been working with the DNR since June to provide the required site information and approval of a corrective action plan which is currently being implemented. We share a strong desire to protect Minnesota waters and the environment and are committed to restoration. We will continue to work closely with the agency on the resolution of this matter."

Calgary, Alberta-based Enbridge's 340-mile Line 3 pipeline will carry a thick Canadian crude across northern Minnesota to the company's terminal in Superior, Wis. The pipeline, which has been roundly opposed by environmental groups and some Ojibwe tribes, is 90 % complete.

Construction started in December. Enbridge pierced the aquifer on the pipeline route near its terminal in Clearbrook sometime the following month, Naramore said.

Enbridge has been pumping the water from the pipeline trench, treating it to remove sediment and releasing into a nearby wetland.

Enbridge had originally told the DNR it would be digging the pipeline trench to a depth of 8 to 10 feet at the site, but the company went down 18 feet and drove piling to a depth of 28 feet, breaching the aquifer, Naramore said.

"They dug deeper than they had represented to us in plans they sent for review," she said. The company did not report the breach to the DNR as it should have, she said.

The DNR discovered something was amiss in mid-June when speaking to independent construction monitors who had observed water pooling in the pipeline trench near Clearbrook, Naramore said.

The Minnesota Public Utilities Commission, when it approved Line 3, required Enbridge to pay for such monitors. Enbridge also needed construction permits from the DNR and the Minnesota Pollution Control Agency before it could start building.

Construction was stopped at the Clearbrook site on June 16 and wasn't resumed until the DNR approved a remediation plan, Naramore said. "What we know is there is damage to the aquifer because it was breached and they need to plug the breach."

She said the DNR was "quite concerned" about the fen, and does not know yet if it is damaged.

Calcareous fens contribute to water quality and ecological diversity. They host several rare and threatened plant species. They are highly susceptible to disturbance, according to the DNR's website. If they are flooded or otherwise damaged, invasive species can move in and crowd out fen vegetation.

The new $3 billion-plus pipeline will replace Enbridge's existing Line 3, which is corroding and operating at only 50% capacity for safety reasons. New Line 3, which partially follows a new pipeline route, will restore the full oil flow, and Enbridge says it is a significant safety improvement.

Environmental groups and Ojibwe tribes say the new pipeline will open a new region of Minnesota's lakes, rivers and streams to contamination from oil spills, as well as exacerbate climate change.