Enbridge needed more than 20,000 cubic feet of grout (concrete) to plug Line 3 aquifer breach near Fond du Lac

A photo essay

In 2021, Enbridge Line 3 construction workers breached an aquifer in St. Louis County, just 400 feet west of the Fond du Lac Band of Lake Superior Chippewa reservation.

Enbridge hadn’t done — nor did the Minnesota Department of Natural Resources (DNR) require — any analysis of the area’s hydrology.

This was one of at least three such aquifer breaches created by Line 3 construction, a violation of Enbridge’s permit and state law.

The St. Louis County breach:

  • Took nearly seven months to repair. (The breach occurred Sept. 10, 2021 and the repair was reported complete on April 7.)
  • Released more than 263 million gallons of groundwater.
  • Required 24/7 grouting activities (think cement) to repair, starting March 8 and finishing April 5 (with two pauses to check for effectiveness).
  • Required more than 20,000 cubic feet of grout to fix, according to Enbridge’s final report on the repair. (That’s enough grout to build a wall two-feet thick, 20-feet tall, and 500-feet long.)

In this part of St. Louis County, Line 3 was crossing a swamp-shrub carr wetland. In the winter of 2020-21, Line 3 workers had driven sheet pilings up to 27 feet into the ground to help keep the construction area dry.

The groundwater release started Sept. 10, 2021, when Line 3 crews used a vibration hammer to loosen and remove the sheet pilings from surrounding soils, likely damaging the artesian aquifer below.

Artesian aquifers contain water under pressure, held down by an aquifer cap, or confining layer. If the cap is broken, the groundwater rushes to the surface.

Artesiasn aquifers typically have clay confining layers, which are relatively strong. Enbridge said the aquifer cap at this St. Louis County site was made up of “native silts and fine sands,” and described it as “fragile.”

It begs the question: Why wasn’t more care taken?

To get a better sense of the breach’s scope, here are photos pulled from inspection reports.

Here’s what the site looked like the day following the breach.

Note sheet pilings, lower left and upper right. Photo Sept. 11, 2021.

A Sept. 11, 2021 inspection report said workers installed silt fence/earthen diversion dams in efforts to pool the water, allowing the silt and other solids settle out. They also used silt fence and straw bales to filter the water before pumping it outside the pipeline’s right of way.

ECD in the caption above is short for “erosion control device.” Photo: Sept. 11, 2021.

Workers also installed “turbidity curtains,” another effort to allow sediment in the water to settle out.

Photo: Sept. 12, 2021.

On Sept. 13, 2021, three days after the breach, an inspector requested “immediate installation” of more erosion control devices, to “further slow the water flow until a plan to contain the water could be discussed.”

At this point, Enbridge management and Barr Engineering were notified of the problem. The Enbridge environmental team began discussing plans to pump out enough water to identify where the groundwater was escaping.

Inserting a dewatering well. Photo: Sept. 16, 2021.

On Sept. 15, 2021 engineers concluded they would need to find a driller “to do further sub-surface investigations to better understand the nature of the groundwater flow through the area.”

Comment: Sept. 27, 2021 memo from Enbridge to the DNR said “No historical geotechnical information was available for this site.” Line 3 crossed 78 miles of wetlands. Where else did Enbridge workers drive sheet pilings deep into the ground without understanding the underlying geology and hydrology?

View nine days after the breach, Sept. 19, 2021.

It would take months to investigate the groundwater flow, develop a corrective action plan, and get it approved. Meanwhile, the aquifer breach kept releasing water, estimated in excess of 263 million gallons.

Below, workers install one of 23 caissons used to aid in dewatering and grout injection. To get a sense of scale, workers spaced 19 of the caissons 30 feet apart along the sheet pile line where the breach occurred. (That’s a line of caissons stretching 540 feet.) The other four caissons were used for dewatering only.

Caissons were used in the dewatering and grout injection process. Photo: Jan. 26, 2022.
Grouting process. Photo: March 10, 2022.

Enbridge has faced no serious consequences for its actions.

One thought on “Enbridge needed more than 20,000 cubic feet of grout (concrete) to plug Line 3 aquifer breach near Fond du Lac

  1. In other words, another preventable tragedy.
    Where were the state and independent monitors watching these breaches unfold again and again???


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