The water pumps were turned off in May after successfully dropping the water levels at Canisteo Mine Pit more than two and a half feet.
The seasonal pumping operation ended on May 14, when water temperatures reached 48 degrees. The DNR's critical decision to pause the pumping is to prevent the transfer of zebra mussel veligers to downstream waters.
The project doesn’t end there. The DNR received legislative funding for construction of the Canisteo outlet. DNR staff will be working on bidding out construction of the fully designed outlet project, which will include further dewatering of the pit. Watch this video to learn more about the project and DNR's future plans for managing pit water levels.
Brief overview
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 May 29, 2023, the Canisteo water level is within 15 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. 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, 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
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 May 29, 2023, the Canisteo water level is approximately 1,309 feet, 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 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.
Canisteo water levels dropped more than two feet
Canisteo water levels dropped from 1311.64 to 1309.07 feet during seasonal pumping this past winter. At this time last year, Canisteo water levels were 1.7 feet higher than they are right now. That means that over the last year, more water was pumped out of Canisteo than the amount of water that went in naturally from rain or snow melt, or groundwater inflow.
Contingency pumping ensured that Canisteo’s water levels stayed below 1318 feet so that the drain tile system in the city of Bovey continues to divert water away from residential structures. Pumping occurred during the winter when pit water temperatures were cold, and zebra mussel veligers were not present in the water, preventing the spread of the aquatic invasive species downstream.
The DNR shut down pumping on May 14, 2023, when Canisteo’s water temperature reached 48 degrees for four consecutive days. The decision to shut off the water pump is crucial to prevent the spread of invasive species. When water temperatures reach 50 degrees or warmer, zebra mussels begin to reproduce, and veligers may be present.
When 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 impact downstream waterbodies. The temperature data will be used to help guide future decisions about Canisteo dewatering projects.
Looking ahead, the DNR is dedicated to continued monitoring, evaluation, and implementation of a permanent outlet structure to manage Canisteo water levels. Money was appropriated by the legislature this season for construction of the Canisteo outlet. DNR staff will be working on bidding 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. Canisteo water levels are expected to rise approximately one to three feet between now and next winter. The DNR will continue to manage water levels until the permanent outlet is constructed.
Permanent engineered outlet planning
Contingency pumping at the Canisteo was a short-term solution to manage water levels until a permanent outlet is constructed. The 2023 legislator approved $8.875 million dollars for construction of an outlet at the Canisteo, which is already completely designed, to provide permanent and year-round water level management.
The construction plans will go out for bid, and then construction could potentially start in 2023. The outlet is designed to be a natural gravity outflow system with built in sand filtration to prevent the transfer of zebra mussels to downstream waterbodies. Water from the Canisteo will ultimately flow into the Prairie River.
Additional dewatering is necessary to make room for construction of the outlet. Residents of Coleraine, Bovey and Taconite should be aware that ongoing dewatering and construction activities will impact recreation on or near Canisteo.
Contact
DNR Lands and Minerals Division
St. Paul, MN
651-259-5689