Tailings basin at Northshore Mine in Silver Bay.
Many people who live in Duluth remember when they had to go to their nearby fire station to collect drinking water. It was 1974, and scientists had found asbestos-like fibers in the city’s water supply. Fire stations installed filters, and two years later a new six-million-dollar water treatment plant was built in Duluth. The fibers came from the Reserve Mining processing plant in Silver Bay, 50 miles up the shore of Lake Superior. The company had been dumping 67,000 tons of tailings (waste rock mixed with water in a slurry) into the lake for 26 years. After a divisive and precedent-setting court battle, Reserve was forced to build a tailings basin inland. The state studied several alternative locations and recommended one at Mile Post 20 (MP20) along the rail route between Reserve’s mine at Babbitt and the processing plant next to Lake Superior. Reserve preferred a site closer to the plant, MP7. After conducting the most thorough environmental study provided for in Minnesota law, an Environmental Impact Statement (EIS), both the DNR and the MPCA concluded that MP7 was not a good location, that the risk of dam failure could not be entirely eliminated, and that a failure would “thwart the entire purpose of on land disposal by emptying stored tailings into Lake Superior.” They denied permits for the facility. The mine appealed, and the Lake County District Court ruled that action was “unlawful, unreasonable, and not supported by substantial evidence.” The case went to the Minnesota Supreme Court, which found the environmental review had not identified any technical faults in the MP7 site but was based on the idea that “it might be prudent to locate the basin further away from Lake Superior and residences.” While acknowledging that “Reserve Mining had an issue with candor in the past,” the Supreme Court concluded that the agencies “had the ability to impose conditions in the permits to guarantee on-going monitoring and supervision” (quoting DNR’s Record of Decision in the current EAW process). The basin now covers about 2,000 acres, perched 600 feet above and just three miles away from Lake Superior, and the current mine’s owner, Cliffs Natural Resources, wants to reconstruct the basin to accommodate more tailings.
The DNR is working on a preliminary review, called an Environmental Assessment Worksheet (EAW) for the proposed tailings pond expansion. Six groups have intervened. Led by the Minnesota Center for Environmental Advocacy, they have formally asked the agency to move on to a more comprehensive EIS.
State law requires an EAW when a tailings pond is expanded by 320 acres or more. In 2016, Northshore proposed raising its tailings basin dams, effectively expanding the basin by about 850 acres. Despite the legal requirement, the DNR announced it would not conduct an environmental review. Environmental groups objected, and in 2020 the company revised its proposal. No longer planning to raise the dam heights, Northshore now plans to extend the length of the dams and move a rail line, reconfiguring the pond to accommodate more tailings. The current plan includes nearly four miles of stream mitigation, needed because the enlarged basin will swallow the lower parts of two trout streams that had already been partially flooded when the original basin was built. That stream work puts the project into a “mandatory EAW” category, and the DNR is now in that process. So far the document consists of 95 pages studying many aspects of the current plan.
Because the laws governing dam safety were not in place until 1979, Northshore does not have a Minnesota Dam Safety Permit. The DNR says its Master Permit takes care of dam safety. The EAW says the current “Factors of Safety for the Mile Post 7 dams exceed the DNR minimum values, and DNR’s review of the most recent round of geotechnical evaluations of Dams 1 and 2 indicate that both dams are robust with Factors of Safety well above recommended levels.” Currently the DNR’s position is that no further environmental review is needed, because a study of dam safety was included in the original 1976 EIS. The environmental groups point out that an EIS is supposed to analyze potential impacts, so any study of dam safety should consider the added tailings, not just those that existed in 1976.
During the 30-day EAW public comment period, which ended May 18, the DNR received so many comments that it is taking an extra 60 days before making a final decision on whether to require an EIS. In a letter to interested parties, the DNR says some of the issues raised by commenters were not discussed in the EAW. One requested a new dam safety study and a modern dam breach analysis. Such studies would include information about the depths, velocities, and paths of the potential tailings flood; discussions of flooding impacts on homes, buildings, businesses, and infrastructure; analyses of harm to wildlife and aquatic life of a potential flood; and the expected effects on long-term air and water quality. They would also consider climate change impacts, including the increase in damaging rainstorms that we are currently experiencing. If an EIS is required, these and other concerns could be investigated.
Now it gets technical
What, you don’t know how taconite tailings ponds are built? Here’s a chance to learn!
First, the ore is mined and partially processed at the Babbitt mine, then transported by train to the plant at Silver Bay where it is further processed. The waste rock is carried up to MP7 by train; it forms the tailings basin’s dams. A slurry of finer waste, mixed with water, is delivered to the pond by pipeline.
Downstream construction. Image courtesy ©Global Tailings Review
It all begins with starter dams that are gradually raised over time. There are two main methods of dam construction: downstream, upstream, plus a hybrid called centerline. MP7 was originally designed as a downstream dam, and it was this method that was studied in the 1976 EIS. As the dam is raised, each new section is built and supported on top of the downstream slope of the previous section (moving away from the basin). This method is considered best for areas with seismic activity and high rainfall or water collection. But during much of the life of MP7, the upstream method was used instead, and currently the company is using the hybrid method. In the upstream method, new sections of dam are placed on compacted tailings above a beach or level area.
Upstream construction. Image courtesy ©Global Tailings Review
Worldwide, several upstream dams have collapsed in the last few years, resulting in catastrophic damage and loss of life. This typically happens when additional weight is placed on uncompacted tailings. Some of these failures were caused by earthquakes, and several South American countries have outlawed upstream dams. According to a mining consultant hired by the environmental groups, Steven Emerman, the essential weakness of upstream construction persists even with centerline construction because dam material continues to be placed on top of fine, uncompacted tailings. He also believes an internal dike in the tailings pond is on the verge of failure, and if it fails, he says it could mimic the impact of an earthquake on the outer dikes. Environmental groups want a study of this issue. The EAW says “the most recent DNR dam safety inspection results indicate the dams are well maintained and are in good condition. There are no major dam safety issues with the present dams at Mile Post 7.”
Centerline construction. Image courtesy ©Global Tailings Review
DNR says its “ongoing regulatory authority” will mitigate possible impacts, but the current EAW makes no reference to monitoring of the dam. According to the environmental groups’ filing, there is a disquieting history of missing or malfunctioning monitoring equipment at MP7. In one example, in 1995, a consultant reported that it had not been considered necessary to replace damaged or malfunctioning equipment over the 19 years since installation. The EAW says those problems have been addressed.
Rules for conducting environmental reviews require that if an agency relies on ongoing regulatory authorities to mitigate possible impacts, mitigation measures must be “specific, targeted, and certain to be able to mitigate” the identified potential harm. Without a dam safety permit or reliable monitoring, it is hard to picture how the DNR’s ongoing authority protects the residents of Silver Bay and the important natural features of the area from dam failure.
Cliffs will need permits not only from the DNR but also from the Minnesota Pollution Control Agency (MPCA) and the U.S. Army Corps of Engineers. In a striking demonstration of how long major projects can take to get permitted, the MPCA’s quarterly status update on projects being managed by the metallic mining unit shows that the agency received Cliffs’ application for an updated tailings basin water pollution permit on April 29, 2021. From that time until the most recent update, in March of 2023, the description of work on this project has been nearly identical. For two years the MPCA has been doing “general work on the permit” as well as “studying groundwater and effluent limits and special conditions.” In each summary, the agency reports that it will “meet with the company as necessary and continue working on the NPDES/SDS (National Pollutant Discharge Elimination System/State Disposal System) permit reissuance.”
The DNR says it will have the final EAW ready on September 1, 2023. If it finds further study is not needed, a court challenge is possible.