A coal ash wastewater leak at a northern Minnesota power plant earlier this week was more than five times larger than original estimates, according to Duluth-based Minnesota Power and the Minnesota Pollution Control Agency.

The utility initially reported about a million gallons of wastewater leaked out of an underground pipe late Tuesday morning at its Boswell Energy Center in Cohasset near Grand Rapids. Now Minnesota Power and the MPCA say about 5.5 million gallons escaped.

Preliminary modeling shows increased levels of sulfate and boron in the area where the wastewater entered a creek that flows into Blackwater Lake, an impoundment on the Mississippi River.

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The leak occurred from an underground pipeline that transfers wastewater from an inactive settling pond that stored ash from coal combustion. The utility used the water in the plant for dust and temperature control.

The spill occurred on land, but a portion of the wastewater flowed to Blackwater Creek and into Blackwater Lake.