Canisteo Mine Pit

Brief history

The Canisteo Legacy Mine Pit (Canisteo) is a pit lake formed in a complex of numerous inactive iron ore mine pits in Itasca County, Minnesota. The Canisteo is located 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. Recognizing the importance of a data record from which water level predictions can be made, the DNR began monitoring for pit water level and surrounding groundwater changes in 1990.

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 September 2022, the Canisteo water level is within 13 feet of the natural overflow elevation. Without pumping, the DNR estimates water would rise at a slow rate, and the pit would naturally overtop by late 2023 or in 2024. If the pit water level were to reach the overtopping elevation, water runout would occur slowly with surface water flowing at the lowest elevations along the pit rim.

The DNR and Iron Range Resources & Rehabilitation have been and will continue working with local communities to identify a long-term solution and seek the legislative funding necessary for construction and operation of an engineered outflow.

 

Canisteo water level management

City of Bovey drain tile system

Map drain tile system in the city of Bovey

Click to enlarge

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

The effects from the already high water table in city of Bovey were worsened by the rising water level in the Canisteo. Groundwater flowed from the pit lake through subsurface materials to the south 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

Water level elevations through August 2022

Graph of the Canisteo Mine Pit water level elevations from December 1989 through August 2022.

Click to enlarge

The DNR Division of Lands and Minerals 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 and continuous logger measurements.

As of August 2022, the Canisteo water level is within 13 feet of the natural overflow elevation. There are two natural overflow locations at elevation 1324 feet 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.

 

Contingency pumping planning

The DNR is working on a contingency plan for pumping water from the Canisteo. The purpose of the contingency pumping is to ensure water levels stay below the recorded high water level of 1318 feet. In August, the Iron Range Resources & Rehabilitation Board approved $710,000 dollars for contingency pumping until a permanent outlet solution is in place.

The DNR planned to begin contingency pumping on October 1, 2022. However, in September 2022, DNR invasive species specialists confirmed zebra mussels in the Canisteo Pit. Zebra mussels are a prohibited invasive species. Before the DNR can begin pumping and discharging water from the pit, the water must first be filtered to eliminate zebra mussel larvae, called veligers, to prevent the spread of invasive species downstream.

The DNR is exploring options for filtering water and will continue to work closely with state and local partners to ensure water levels do not impact surrounding communities while also complying with invasive species prevention requirements.

As of September 19, 2022, the pit water level was at 1,311 feet. The current elevation is more than six feet below the historic high elevation of 1,318 feet, at which the drain tile system in Bovey remained effective at diverting groundwater away from residential structures located within the city. Current data indicates a slow rise in the pit water levels. If a filter system can not be acquired, installed and tested to remove veligers before winter 2022, winter pumping will provide water level management.

 

Permanent engineered outlet planning

The $710,000 for contingency pumping at the Canisteo Pit is a short-term solution to prevent water from overtopping the pit until a permanent outlet solution is in place. A permanent solution will require legislative funding. The DNR is continuing work with State agencies, local units of government, and private entities to discuss and plan for the permanent engineered outlet project. A hired consultant is working to finalize the engineering and design, and update plans and specifications for bidding the project.

Once legislative funds are available, construction of the outlet structure is estimated to take one year to complete. If the Canisteo water level continues to rise at a slow rate similar to those in recent years, water may begin to naturally overflow by 2023-2024.

 

Contact

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