To build the new Line 3 pipeline across northern Minnesota, the Enbridge Energy company needs to dig a trench — and temporarily pump groundwater out of the construction area, in a process called dewatering.
Enbridge originally asked for permission to pump about 510 million gallons of water from the pipeline corridor, as it builds the replacement to the current Line 3 pipeline along a new, 340-mile route across northern Minnesota.
But as construction moves forward, the company encountered more groundwater than it anticipated and requested to significantly increase the amount it’s authorized to pump, according to the Minnesota Department of Natural Resources.
On June 4, the DNR issued an amended permit that allows Enbridge to pump up to nearly 5 billion gallons — almost 10 times more than the original amount the company had requested — for the remaining 145 miles of pipeline it has left to build.
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Opponents of the project worry that the pumping could reduce the overall quantity of groundwater and potentially affect sensitive wetlands, lakes and streams along the route, which are already under stress due to current drought conditions statewide.
But the DNR says it has determined that the increase in dewatering would not threaten groundwater sustainability or have other harmful impacts on natural resources.
The agency’s permit only allows Enbridge to pump shallow groundwater from the construction area, not from lakes or wetlands, said Randall Doneen, a senior DNR administrator who oversees ecological and water resources. The water is temporarily stored and treated, then discharged nearby, where it infiltrates back into the ground, he said.
“Our assessment is that the actual pumping of it will have limited impact to the wetlands, streams and lakes and the shallow aquifer,” Doneen said.
Dewatering to dig a trench
Dewatering is required for construction projects like new roads, buildings or sewer lines that require digging a hole or trench, which tend to fill with water if they’re below a certain depth.
“Everywhere that you go down into the ground, you eventually run into the water table,” explains Kelton Barr, a consulting hydrogeologist who’s worked on other dewatering projects in Minnesota, but is not involved in Line 3.
“Below that point, the ground and all the pores in it are saturated with water,” Barr said. “And so, if your construction project needs to be doing things below that water table, then you have to do dewatering.”
Large dewatering projects — those that involve removing more than 10,000 gallons a day, or 1 million gallons a year — require a permit from the Minnesota DNR.
In an email, Enbridge spokesperson Juli Kellner attributed the need to pump more water in part to the company’s decision to use more wellpoint systems — a series of wells installed along the excavated trench that lower the shallow groundwater.
Dewatering with wellpoints produces cleaner water with less dirt and sediment than pumping water out of the trench with a sump pump — a traditional method of dewatering, Barr said.
Sediment — loose particles of sand, clay, silt or other material — makes water cloudy and is harmful to fish and aquatic life.
“Usually you're trying to keep the water from being too muddy,” Barr said. “A lot of fine [material] can get into the water, especially from just excavation. That makes it more likely to be a water quality problem.”
The permit the DNR granted to Enbridge specifies that water removed from the construction trench cannot be discharged directly into a surface waterway, such as a lake or wetland. It must be run through a large fabric bag that allows any sediment to filter out, then it is discharged into a well-vegetated upland area — or, in certain cases, a constructed stormwater pond.
Doneen said state regulators don’t believe the temporary removal of the water has much potential to impact wetlands, streams and lakes, because it’s short-term. Under the amended permit, Enbridge must discharge the water within three days in most cases.
Regulators’ larger concern, Doneen said, is how Enbridge will store and replace that volume of water, making sure that — when it’s released — it doesn’t contain sediment that could harm aquatic ecosystems.
“That's what we've seen with pipeline construction in the past,” he said. “That's a lot of water, and you have to be able to manage it carefully.”
As part of the amended permit, the DNR and the Minnesota Pollution Control Agency added requirements for Enbridge to take additional precautions, Doneen said.
Those precautions include having trained Line 3 employees monitor the locations where the water is discharged; not discharging near small, isolated wetlands that can’t handle the additional water; and adding extra barriers, such as silt fences, around temporary water storage ponds that are close to lakes or rivers.
“They can't have discolored water. They can't harm aquatic ecosystems,” Doneen said. “It has to be handled in a way that doesn’t create nuisance conditions.”
Worries about potential impacts
Still, some Ojibwe tribes in northern Minnesota worry that the increased pumping of groundwater could exacerbate current drought conditions and threaten the health of wetlands and lakes where wild rice grows. An important cultural and economic crop for Ojibwe tribes, wild rice can be stressed by changing water levels.
Leaders of the White Earth Nation pointed to low water conditions at Upper and Lower Rice lakes, near the Mississippi River headwaters.
“Given that we find ourselves in a moderate drought, with higher than average temperatures and lower than average precipitation, displacing this amount of water will have a direct detrimental impact on the 2021 wild rice crop,” wrote Michael Fairbanks and Alan Roy, tribal chairman and secretary-treasurer of the White Earth Nation, in a letter to the president of the Minnesota Chippewa Tribe, a centralized government that unites six Ojibwe tribes in northern Minnesota.
Roy and Fairbanks were asking the Chippewa Tribe in their letter for support in calling for the permit to be rescinded.
White Earth leaders say the Minnesota DNR issued the amended permit without consulting them. The DNR disputes the assertion, saying it notified tribes via email and met with tribal representatives in May.
The DNR’s Doneen said water is not being pumped from Upper and Lower Rice lakes for the Line 3 project. He said his agency is aware of the tribes’ concerns about those lakes’ low water levels and is working with White Earth officials on their concern about wild rice.
But on a broader scale, environmental groups and others that oppose Line 3 question why Enbridge so drastically misjudged the amount it would need to pump along the new route across northern Minnesota, which is dotted with lakes, streams and wetlands.
Laura Triplett, an associate professor of geology and environmental studies at Gustavus Adolphus College in St. Peter, has testified against Line 3. She argues that the company’s statement that it encountered more groundwater than expected “demonstrates a fundamental misunderstanding" of the region where the pipeline is being built.
“I think DNR should not have approved this without a much deeper inquiry into what else Enbridge doesn't understand about Minnesota’s water,” she said.
Triplett argues that while Enbridge is pumping the water for only a short time, the company doesn’t know how quickly the water will return to the aquifers it came from. And she worries about the impact of increased pumping on wetlands if they’re not recharged right away.
“It could be pretty disruptive to some ecosystems,” she said.
Hydrology experts said that dewatering does come with potential impacts, including the possibility that less water might make its way back to wetlands that are hydrologically connected. But they said those are usually short-lived and shouldn’t be a problem once the water table is allowed to return to normal.
However, there are some potential longer-term impacts, such as soils around wetlands getting compacted after the water is pumped, Barr said.
“The drainage of the water out of those peaty soils could end up compacting the soil, so it actually sinks a bit and consolidates,” he said. “When the dewatering is finished, now the water would be deeper there.”
Ongoing legal challenges
Enbridge says the existing Line 3 pipeline needs to be replaced because it was built in the 1960s and is deteriorating. The Calgary-based company says the new pipeline will be safer and less likely to leak, as it carries crude oil from Alberta’s tar sands to Enbridge’s terminal in Superior, Wis.
Opponents of the project argue that it will exacerbate climate change, threaten waters and infringe on tribal members’ rights to hunt, fish and gather on treaty lands.
In recent weeks, activists have ramped up protests, occupying pipeline easements, organizing marches and prayer vigils and, in some cases, halting construction by chaining themselves to equipment.
Enbridge says construction on the Line 3 project is more than half complete. It expects the pipeline to be in operation by the fourth quarter of this year.
Still, several legal challenges to the project remain, including an appeal of Line 3’s state and federal water permits.