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.Map Photo of Bovey 1st Ave Drain Tile System - Proposed Alignment
- Outflow to stabilize Canisteo Pit water level
DNR is moving forward with designing and constructing a gravity-fed flowage route out of the west end of the Canisteo Pit. This system of interconnected pipes will divert 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.
Canisteo Pit Area and General Project Map
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.
- The base course of bituminous has been laid down and final wear course is planned for late spring 2012, consistent with Itasca County plans for CR61/2nd Avenue reconstruction.
- Roadways along the drain tile system have been paved with a base coat of bituminous. Roadside restoration will continue for the next few weeks into November with reshaping and reseeding with dormant seed.
Prairie River Outflow
- A Request for Proposals (RFP) for hiring a design engineer was issued in November 2010.
- Barr Engineering was been selected as the Phase I design engineer for the project.
- Geotechnical borings were completed the week of January 24 and baseline water quality sampling occurred the week of January 31, 2011.
- Phase I of the engineering design included an evaluation of alignment and alternative designs. This evaluation determined a final design and set the long-term, stable water level elevation of the Canisteo.
- The alternative that was selected combines open channel flow and pipe from the Canisteo Pit to the West Hill Pit. The design that was selected will allow for an ultimate Canisteo Pit water level of approximately 1305 MSL. This will equate to a Canisteo Pit water level drop of 11+ feet from its current level.
- Barr Engineering received their Notice to Proceed the week of January 9, 2012 for Phase II (Final Design) and Phase III (Construction Oversight).
- A second (and perhaps final) round of geotechnical borings along the outflow route will begin the week of February 13, 2012.
- RFPs for construction and subsequent construction of the Prairie River Route is expected to begin in mid 2012, pending the DNR obtaining property easements.
Canisteo Pit Water Levels - Current and Historic
• Most Recent Pit Water Level - 1316.23 MSL (January 20, 2012)
• The water level in the Canisteo is expected to continue to rise until an outflow is constructed. Expected approximate Canisteo Pit water level by Prairie River Route construction ~ 1317 MSL.
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Contact
Mike Crotteau
Mining Hydrologist
DNR Division of Ecological and Water Resources
1201 East Highway 2
Grand Rapids, MN 55744
(218) 999-7893