Canisteo Mine Pit Outflow Project
A brief history
The Canisteo Pit is a large lake formed in a complex of 19 inactive mine pits located immediately north of Coleraine, Bovey and Taconite in Itasca County, Minnesota.
Canisteo Pit is about 4.8 miles long and averages one-half mile wide. The pit lake averages 100 feet deep with its deepest point at nearly 300 feet. The water surface area is approximately 1,425 acres (2010); the volume of the pit is about 150,000 acre-feet.
Mineral exploration in this area began as early as 1888. Iron ore shipping began in 1907 and continued until September 1985. Water was pumped out of the pit until mining ended in 1985. After that, water levels in the pit began to rise from about Elevation 1000 to the July 2010 level of Elevation 1315.3 feet Mean Sea Level (MSL).
What is the issue? Why the need for action?
Active mining in the pit complex ended before enactment of the Mineland Reclamation Rules. Those rules require mining companies to resolve environmental issues such as reclaiming lands and watersheds when mining ends. This makes the Canisteo Pit complex an "orphan" of past mining operations.
After mining and subsequent pit dewatering stopped, the pits began to fill with water from precipitation and natural ground water inflow. As the pit filled with water and water levels increased, people became concerned about possible uncontrolled water outflow and pitwall erosion.
Since 2001, federal, state, and local governments have studied the problems of the rise in pit water levels, the impacts of water on pitwall stability, and development of an outflow plan for the pit water. A plan has been developed to address these concerns.
Pitwall stabilization efforts along the south, east and west pitwalls of the Canisteo are very important, particularly in areas immediately north of Bovey. Stabilization efforts could include laying back pitwall glacial sediments, terracing, use of geotextiles and vegetation, rip-rap, etc. However, pitwall stabilization efforts will not be fully effective until pit water levels are stable so submergence and undercutting of those efforts do not occur. Therefore, before developing a more in-depth plan for stabilizing pitwalls, a stable pit water level must be established. That stable water level will be part of the engineering design for the outflow project.
DNR's role in the Canisteo Outflow Project
Under Minnesota Law (Minnesota Session Laws - 2008, Chapter 179, Sec. 7, Subd. 3), the Commissioner of DNR is responsible for betterments built for Canisteo. This includes ownership, operation and maintenance.
Plan and Implementation
As of May 2010, the Commissioner of DNR decided to complete engineering design plans and construct two systems to alleviate the high water table in Bovey and to stabilize the water level in the Canisteo Pit.
Drain tile system to address high water table in Bovey
Bovey has, for many years, experienced high water table issues affecting residents' basements and city infrastructure. In addition, in recent years, the rising pit water of the Canisteo has influenced the local water table in the lower areas of the city. Water leaving the pit through glacial sediments (groundwater outflow) has caused localized increases in the shallow groundwater beneath the city. This has made pre-existing water table issues worse.
No solution will reduce the Canisteo Pit water level to a point where it will not influence the Bovey water table. One proposed solution, perpetual pumping, is not a viable, nor cost effective. Another proposal, to divert waters via gravity to other water bodies will not work because all receiving waters surrounding the pit are at too high an elevation. Therefore, the best solution to alleviate high water table issues in the area most impacted (1st Avenue) is to construct a drain tile system that will intercept groundwater leaving the pit before it reaches the homes. Intercepted groundwater will then be directed into an underground pipe before day-lighting in a ditch along lower 2nd Avenue, which ultimately leads to Trout Lake.
Outflow to stabilize Canisteo Pit water level
Up until December 2012, DNR proceeded with design and construction of a gravity-fed flowage route out of the west end of the Canisteo Pit. This system of interconnected pipes would divert Canisteo flow through existing wetland/depression areas previously impacted by mining. Water from the Canisteo will go to abandoned mine pits (West Hill and Lind) before ending up in the Prairie River.
However, in light of current and potential future increases in Canisteo water use coupled with construction bids greatly exceeding budget amounts, DNR has canceled plans at this time for the construction of the Canisteo - Prairie River Outflow Project. See below for details concerning the future pit water levels.
Pitwall stabilization in the future
When the final pit water level elevation is determined, plans can begin to stabilize certain areas of the pitwall.
Status of Projects
Bovey 1st Ave Drain Tile System
- Design engineer, Short Elliot Hendrickson, Inc. (SEH), was selected for design and construction oversight of the Bovey 1st Ave drain tile system.
- Bidding for construction began May 15, 2011. Bids from construction contractors were due June 8, 2011. Casper Construction was selected as the construction contractor for the Bovey 1st Ave drain tile system.
- Construction of the drain tile is complete and functioning well. Drain tile flow averages between 30 and 60 gallons per minute and outlets to a storm water ditch to Trout Lake.
- The final wear course of bituminous has been laid down and project completion occurred July 2012.
Canisteo - Prairie River Outflow Project
- Project construction has been canceled at this time due to current and potential future increases in Canisteo water use coupled with construction bids greatly exceeding budget amounts.
Canisteo Pit Water Levels - Historic, Current and Future
Most Recent Pit Water Level - 1314.40 MSL (October 9, 2013)
The water level in the Canisteo is expected to decline for the next five to fifteen years due to Canisteo water use. However, episodic increases in pit water level will occur during spring runoff and summer rainfall events.
DNR Division of Ecological and Water Resources
1201 East Highway 2
Grand Rapids, MN 55744