State utility regulators on Thursday approved the environmental review of Enbridge’s proposed new crude oil pipeline across northern Minnesota, a milestone for the controversial project.

By a vote of 5-0, the Minnesota Public Utilities Commission (PUC) deemed the environmental impact statement (EIS) for Enbridge’s proposed new Line 3 to be “adequate.” The PUC in December had voted 4 to 1 against the EIS, saying it was inadequate because of a handful of narrow concerns.

The PUC sent the report back to its author, the Minnesota Department of Commerce, to address its questions. PUC members said they were satisfied with the answers.

“The revised EIS before us addresses the significant environmental issues,” said PUC Commissioner Matt Schuerger. The EIS looks at myriad potential environmental effects of a new Line 3 but made no conclusions.

In June, the PUC is scheduled to decide on a “certificate of need” for the project — essentially giving it a green light or killing it.

Environmental groups and Indian tribes that oppose Line 3 have criticized the EIS on several fronts, including not adequately assessing potential oil spills into sensitive waters or wilderness areas.

They continue to say the EIS is inadequate, and a legal challenge of the PUC’s decision is in the offing. The environmental activist group Honor the Earth plans to appeal the ruling to the Minnesota Court of Appeals, according to Paul Blackburn, an attorney for the group.

“We believe the environmental impact statement doesn’t fully address the impacts on the indigenous people of Minnesota and all of the people of Minnesota,” Blackburn said.

Commissioner Nancy Lange, the PUC’s chairwoman, said the panel “is on solid ground” with the EIS.

“What reviewing courts may do, that’s outside of our ability to predict,” she said.

PUC vice-chair Dan Lipschultz said the EIS gives the commission a “tool” to help in its final Line 3 decisions.

“This is really an important document, a very comprehensive document,” he said. “Does it fall short of perfect? Does it fall short of what I like? Of course it does.”

Calgary, Alberta-based Enbridge said the new pipeline — a $2.6 billion project — is a much-needed safety upgrade. The 1960s-vintage Line 3 operates at 51 percent of its capacity due to safety concerns. The new Line 3, which would carry oil from Canada, would restore full capacity.

In a statement Thursday, Enbridge said the EIS was the most extensive environmental review of a pipeline project in Minnesota.

“We would like to thank the Department of Commerce and the supporting agencies for their considerable work in developing the EIS,” the company said.

Under Enbridge’s proposal, the new pipeline would run along the current path of Line 3 to Clearbrook, where it would jog south before heading east to Enbridge’s big terminal in Superior. Opponents said a new Line 3 would expose a new region of Minnesota — including pristine lakes and wild-rice waters — to degradation from oil spills.

When the PUC rejected the EIS in December, it asked the commerce department to provide more information on whether one alternative to Enbridge’s proposed pipeline route could be tweaked to avoid sensitive geologic formations known as “karst.”

The PUC also asked the Commerce Department to provide more clarity on how it weighted certain environmental calculations of Line 3 and several alternative routes.

In addition, the PUC required that the final EIS state that if Line 3 is eventually approved, construction can’t begin until a tribal cultural survey is completed.

While Line 3 does not cross any Indian reservation, it would traverse the tribes’ traditional homeland. The EIS includes an analysis of tribal properties, but it includes only known archaeological and historic resources.

The full tribal cultural survey is broader, and it involves searching for sites that aren’t necessarily known. The tribes and Honor the Earth have maintained that the EIS isn’t adequate until a full tribal cultural survey is done. The commerce department agrees that one needs to be done but said it should be led by the U.S. Army Corps of Engineers.

The tribal cultural survey has had many delays, Sara Van Norman, an attorney for the Fond du Lac Band of Lake Superior Chippewa, told the PUC on Thursday. The tribes are consultants on the survey, and Fond du Lac is the main tribal liaison for the Line 3 project.

“We need to get this done, and we could have had it done,” she said.

Now, she said, “through no fault of our own,” the field work won’t be done until August or September.

Joe Plumer, an attorney for the White Earth Band, told the PUC the tribal cultural study “is no rote exercise.”

A tribal cultural survey “was the exact issue at stake” in the protests by the Standing Rock tribe in North Dakota against the Dakota Access pipeline, he said. Massive protests occurred in late 2016, led by the tribe, which was concerned that a pipeline break would pollute its drinking water.