The Canisteo 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. This may include water level management. 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 party is responsible for managing water levels.
As water levels continued to rise 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 needed for the Canisteo to prevent future flooding and impacts on nearby communities. While this area may still be a viable option for future mining operations, which may include pumping water from the pit, an engineered outlet structure is the only guaranteed method to control water levels.
Canisteo water level management
City of Bovey drain tile system
After iron ore mining and subsequent pit dewatering ceased, 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 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 9/1/2021
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 represents a combination of manual measurements and continuous logger measurements.
As of August 2021, the Canisteo water level is within 15 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 directly 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.
Engineered outlet planning
Between 2018 and 2020, State agencies worked collaboratively to gather water quantity and quality information from the Canisteo, as well as from nearby surface waters that may serve as receiving waters for any constructed outlet.
The DNR is continuing work with State agencies, local units of government, and private entities to discuss and plan for the outlet project. A hired consultant is working to finalize the engineering and design, and update plans and specifications for bidding the project.
Additional funds will be needed to complete the Canisteo outlet project, which include construction. Construction is estimated to take one year to complete. If the Canisteo water level continues to rise at a rate similar to those in recent years, water may begin to naturally overflow by 2023-2024.
DNR Division of Lands & Minerals
St. Paul, MN