The water, which was being siphoned off the top of an old coal ash pond for re-use at the Boswell Energy Center in Cohasset, Minn., escaped from a break in an underground bend in the pipe, according to Josh Skelton, Minnesota Power's chief operating officer. The point of failure was shortly before a section where the pipeline rises above ground and then crosses Blackwater Lake on a trestle, he added.
"Spills do occur in our processes. We work hard to mitigate impacts, whether they're a million gallons or less than one gallon," Skelton said. Still, he acknowledged that "the million gallons is more than we've had [in past events]."
The Duluth-based electric utility spotted the leak when it found standing water that bubbled to the surface near the break site. The water poured out over land, with at least some reaching Blackwater Lake.
Minnesota Power said the leak has been contained and the company is monitoring for potential impacts to water and wildlife, and also notified the Minnesota Pollution Control Agency and the Environmental Protection Agency. Skelton said earthen berms and booms were being put into place to contain the spill.
MPCA is investigating the spill, spokeswoman Andrea Cournoyer said in a statement.
According to a report to the state duty officer, the spill was discovered at 11:15 a.m. Tuesday. The report was made 15 minutes later, and Minnesota Power said a "loss of pump pressure" caused the spill.
But that loss of pressure wasn't actually the cause, Skelton said — rather, it signaled something was wrong, because water wasn't flowing into the plant at the typical rate.
Before Minnesota Power stopped putting ash in the pond in 2015, it was part of scrubbing technology to capture and store the leftovers from combusting coal. Since then, Minnesota Power draws the water back to the plant for several uses, including to tamp down dust from unloading dry ash into trucks.
"Our goal is to dewater that pond towards the end of the life of the coal operations here at Boswell so we can retire the ash ponds," Skelton said. "So you've got to get rid of the water from the ponds from the original construction."
The plastic pipe to transport that water was installed around 2014 or 2015, Skelton said. Company spokeswoman Amy Rutledge said the company isn't sure yet how long the pipe had been leaking.
Skelton said the water isn't treated between the pond and the plant. Waste is meant to settle at the bottom of the pond, though the water can still carry pollutants. The company has been working to capture some of the water and return it to the pond.
MPCA met with the utility and a contractor conducting cleanup the same day the leak was found, Cournoyer wrote. The agency, along with the company and the EPA, are working to find ways to mitigate environmental damage from the spill.
Coal ash contains pollutants including mercury, cadmium and arsenic, which can pollute water and air if not properly managed, according to the EPA. The pond where Minnesota Power was taking water was used between 1980 and 2015 to dispose of fly ash, or fine particles that are carried by the flue gases in a plant.
"The leak likely began from an underground pipe and surfaced where the pipe extends above ground," Cournoyer wrote. "The wastewater flowed to [Blackwater] Creek and into [Blackwater] Lake."
The 674-acre Blackwater Lake is a reservoir on the Mississippi River, according to the state Department of Natural Resources. Lake levels are controlled by the Pokegama Dam operated by the U.S. Army Corps of Engineers. Minnesota Power draws water from the lake to cool its plant and releases heated water. The DNR describes the lake as "essentially a flooded river channel." A bay where the DNR said the coal plant discharges heated water attracts fish and is popular with anglers, according to the agency.
It's still unclear how far the material may have spread. Walter Shadley, Cohasset's public works and utility supervisor, said the town does not draw its drinking water from the Mississippi.
Steve Robertson, assistant manager of the Minnesota Department of Health's Drinking Water Protection section, said based on early information, "the risk is low" to local drinking water.
"Given the nature of the aquifer, the effects of the spill, if any, would be on the order of a year or more away. We will assess any other potential risks to public water systems in the area as we receive more information about the spill," Robertson said in a statement.
The Boswell plant is Minnesota Power's largest electricity source. Its two operating coal-fired units are capable of producing 932 megawatts of electricity. One unit at the plant is scheduled to retire in 2030, and the second is slated to close in 2035 as the utility transitions to carbon-free power to meet its climate goals and state regulations for a carbon-free grid by 2040.
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