The proposed expansion of Northshore Mining’s giant Peter Mitchell taconite iron ore mine near Babbitt won’t need a full-fledged Environmental Impact Study, a state agency has determined.

The Minnesota Department of Natural Resources announced Thursday that the expansion of the Cliffs Natural Resources operation can proceed now

that a cheaper and less time-consuming Environmental Assessment Worksheet has been completed.

Environmental groups had pushed for the full Environmental Impact Statement. But DNR officials said they made the decision based on the extent of anticipated environmental effects, potential cumulative impacts and past studies of other projects that can help predict likely impacts.

The project includes mining an additional 108 acres and constructing an engineered stockpile to manage sulfur-bearing waste rock. That’s the kind of rock that, when exposed to air and water, can spur acidic runoff that can leach heavy metals out of the landscape. High sulfur levels also can damage wild rice.

The expansion will extend Northshore operations up to 10 years, although the mine could operate another 70 years, the DNR noted.

The company now can seek permits to begin construction of the expansion. The project is subject to ongoing regulatory authority by the DNR, the Minnesota Pollution Control Agency and the U.S. Army Corps of Engineers.

A Cliffs spokeswoman in Cleveland did not immediately return a request to comment on the DNR decision.

Paula Maccabee, attorney for the group Water Legacy, said it appears the DNR “missed the point’’ of her comments and those of other environmental groups.

“Failure to require an Environmental Impact Statement before expanding into high-sulfur rock at the Northshore Mine is reckless,’’ Maccabee said. “Even the modest level of testing that has been done so far shows that the Virginia Formation rock sampled would result in acid mine drainage. Levels of toxic metals were also tested to be above chronic water quality standards that protect aquatic life. Yet, without an EIS, there is no consideration of any alternatives to control pollution from newly exposed high-sulfur rock.”

Maccabee said the DNR’s decision has a major error, stating that the state’s wild rice sulfate limit doesn’t apply to the expansion project because there is no wild rice downstream. In fact, Maccabee noted, the Minnesota Pollution Control Agency lists the Dunka River and Birch Lake as wild rice waters.

Taconite iron ore that is mined in the Peter Mitchell pit is moved by train to Silver Bay, where it’s concentrated and processed into pellets at the Northshore facility, formerly Reserve Mining Co., before being moved by boat to steel mills on the Great Lakes.

Northshore Mining has nearly 600 employees and produced 3.8 million tons of taconite in 2013, the most recent year for which state-verified numbers are available.