Canisteo Mine Pit

Brief overview

The Canisteo Legacy Mine Pit (Canisteo) is formed by a complex of inactive iron ore mine pits that have filled with water. The Canisteo is located in Itasca County, Minnesota, north of the cities of Coleraine, Bovey, and Taconite.

Traditional iron ore mining began in the Canisteo in 1907 and continued through 1980. Mineland Reclamation Rules for ferrous mining were adopted in 1980, requiring mining operations to plan for closure and reclamation. Between 1980 and 1986, mining in the Canisteo consisted exclusively of scram operations. Reclamation was only required for disturbances connected to scram mining operations and not water level management. Therefore, the Canisteo is considered a legacy mine pit and no company is responsible for managing water levels.

The DNR's role in managing water at a pre-1981 site like the Canisteo Legacy Mine Pit, similar to numerous other water challenges across the state, is to provide technical expertise for and regulatory oversight of any water appropriation or work in public waters in accordance with Minnesota Statute 103G.

As water levels rose within the Canisteo, the full extent of potential hydrologic impacts to surrounding communities was unknown. To address this, the DNR began monitoring for pit water level and surrounding groundwater changes in 1990 in order to create an important data record from which water level predictions could be made.

An engineered outlet structure is necessary to control the pit's water levels in a way that doesn't adversely affect surrounding communities. As of November 2024, the Canisteo water level is around 1,304 feet, which is 20 feet below natural overflow. Without a permanent outlet, the DNR estimates water would rise at a slow rate, and the pit would naturally overtop. Any runout would be a trickle amount at the lowest elevation of the pit rim at 1,324 feet, which would not pose an imminent threat to public safety and would allow time for the DNR to address the issue.

The DNR and the Department of Iron Range Resources & Rehabilitation (DIRRR) have been and will continue working with local communities to implement a long-term solution. Legislative funding is now available for construction and operation of an engineered outflow.

Canisteo water level management

After iron ore mining and subsequent pit dewatering ended, the Canisteo began to fill with water from precipitation as well as both surface water and groundwater inflow. The increasing pit water level created concerns within nearby communities, including a rising water table within the city of Bovey. In response to these concerns the DNR conducted various studies to evaluate potential impacts from the rising pit water level.

The results of these studies indicated the effects from an already high water table in city of Bovey were worsened by the rising water level in the Canisteo. Groundwater flowed from the pit through subsurface materials toward the city. In 2011, the DNR designed and constructed a drain tile system along 1st street. The drain tile system diverts groundwater away from residential structures located within the city.

In 2012, the DNR issued a water appropriation permit to Magnetation LLC, a scram mining operation, authorizing the pumping of water from the Canisteo for mining operations. This pumping resulted in a decrease in the water level until Magnetation LLC filed for bankruptcy in 2015. Pumping ceased in 2016, resulting in a rising pit water level.

ERP Iron Ore LLC acquired Magnetation LLC assets and resumed intermittent pumping in 2017. Pumping again ceased in 2018 when ERP Iron Ore LLC entered bankruptcy, and the water level in the pit began rising again.

Water level monitoring

The DNR Lands and Minerals Division actively monitors the Canisteo water level and surrounding groundwater levels to understand the rate of pit water level increase and groundwater flow through the subsurface materials. Hydrologic information gathered near the pit informs assessment of the need for an engineered outlet structure to prevent future flooding and other impacts. The city of Bovey drain tile system is monitored for flow and system efficiency. The Canisteo water level trend shown above represents a combination of manual measurements (dashed line) and continuous logger measurements (solid line).

As of November 4, 2024, the Canisteo water level is around 1,304 feet, which is 20 feet below natural overflow. Two natural overflow locations at elevation 1,324 feet have been identified along the pit rim, one of which is located north of the city of Bovey. Groundwater level monitoring indicates that groundwater outflow from the pit moves to the south. The current hydrologic conditions in nearby communities demonstrate the need to design and construct an engineered outlet for the Canisteo.

Looking ahead, the DNR will contract for the construction of a permanent outlet structure to manage Canisteo water levels. The 2023 Minnesota Legislature approved $8.875 million in bonding funds to construct an outlet at Canisteo, so the next step is for DNR staff to bid out construction of the fully designed outlet project, which will include further dewatering of the pit.

Water rises in the pit naturally due to rainfall, snow melt and groundwater. The DNR will continue to manage water levels if necessary until the permanent outlet is constructed.

Canisteo water levels dropped more than eight feet

The Department of Natural Resources turned off the water pumps at the Canisteo Mine Pit, marking the end of the second season of winter contingency pumping. For the last two winters into early springtime, water pumping operations have been running 24 hours a day to reduce the water level in the Canisteo pit and prevent it from overtopping.

During the last pumping season, the water levels in Canisteo dropped from 1,309.53 to 1,303.65. Over the past two years since pumping began, more than five billion gallons of water have been moved from the Canisteo into a wetland complex and Holman Lake, decreasing water levels in the pit by eight feet.

Contingency pumping ensured that Canisteo’s water levels stayed below 1318 feet so that the drain tile system in the city of Bovey continued to divert water away from residential structures. Winter pumping also made sure that Canisteo water temperatures were cold, and zebra mussels were not in the water, preventing the spread of aquatic invasive species into the wetland complex and Holman Lake.

The DNR shut down water pumping activities on May 10, 2024 , when Canisteo’s water temperature increased to 48 degrees for four consecutive days. The decision to shut off water pumps is crucial to prevent the spread of invasive species. When water temperatures rise to 50 degrees or warmer, zebra mussels begin to reproduce, and immature zebra mussels called veligers, which are an invasive species, may return to the water.

Before pumping started, DNR installed telemetry temperature monitoring and downstream water monitoring equipment that allowed DNR hydrologists access to temperature and water level data remotely and in real-time.

Data from monitoring activities helped DNR scientists determine water levels and how much water was pumped out of Canisteo. The data was also important to help make sure pumping didn’t cause damage to downstream water bodies. The temperature data will be used to help guide future decisions about Canisteo dewatering projects.

The Canisteo contingency pumping project is the first step in building a permanent water outflow. The construction plan for a permanent outlet structure will go out for bid soon and work could start in the fall of 2024.

Water rises in the pit naturally due to rainfall, snow melt, and groundwater. Based on the latest predictions by DNR scientists, water levels would not be expected to reach the natural overflow elevation until after 2040.

 

Permanent engineered outlet planning

Contingency pumping at the Canisteo is a short-term solution to prevent water from overtopping the pit until a permanent outlet solution is in place. The bonding bill has passed and legislative funding is available. DNR will begin the process of constructing the outlet, which is already completely designed.

The construction plans went out for bid in the summer of 2024, and construction could potentially start in the fall of 2024. The outlet is designed as a gravity outflow system with sand filtration built-in to prevent the transfer of zebra mussels to downstream water bodies. The gravity outflow structure will flow into the Prairie River and provide year-round water level management, which eliminates the need for seasonal pumping.

The DNR has no plans to open public access at the Canisteo. If you are planning to access Canisteo, please ensure that you have permission from the landowners. Residents of Coleraine, Bovey and Taconite should be aware that ongoing dewatering and construction activities will limit recreation near the pit.

Contact

DNR Lands and Minerals Division
St. Paul, MN
651-259-5689