The St. James Legacy Mine Pit is a pit lake located north of the city of Aurora in St. Louis County, Minnesota. Natural iron ore was mined from the St. James and shipped between 1916 and 1963.
Currently, the city of Aurora utilizes the pit water for the city’s municipal water supply. The city’s municipal water supply pump house (pump house) is located near the current water’s edge. The water level elevation was 1441.35 feet above mean sea level (msl) on May 29, 2023 with the pump house floor elevation at 1444.27 feet msl.
Adopted in 1980, the Mineland Reclamation Rules for ferrous mining require mining operations to plan for closure and reclamation, which may require water level management. For operations that ceased prior to the adoption of the Mineland Reclamation Rules, such as the St. James Pit, reclamation was not required. Therefore, the St. James Pit is considered a legacy mine pit and no party is responsible for water level management.
St. James water level management
Though water from the St. James Pit is used for the city of Aurora’s water supply, the demand is less than inflows to the pit resulting in rising water levels. The pit receives water from precipitation and both surface water and groundwater inflows. Rising water in the St. James Pit has prompted the city to manage water levels to protect the pump house from flooding. Due to the recent discovery of zebra mussels in the St. James Pit, the DNR is working with the city of Aurora to determine appropriate treatment and monitoring for any water discharged from the pit for the purpose of water level management.
Historic water level data are relatively limited to periods of pumping. Thus, the rate of water level rise and ultimate static elevation are unknown absent pumping. The City of Aurora received LCCMR funds to study the St. James Pit for the purpose of creating a water balance model and estimating final pit water levels if pumping from the pit were to cease. Data collection and work is underway to assist in modeling efforts, inform decisions, and aid in the assessment of possible impacts from rising water levels. Work includes a bathymetric survey of the St. James Pit, groundwater well installation, water modeling, and surveying. DNR staff are coordinating with the city and their consultant on the study and providing data and technical expertise. DNR completed the bathymetric survey of the St. James Pit in July 2022.
An engineered outlet and route may be needed in the future should pumping cease. 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. If a preferred outlet location and route are chosen, future phases would include predesign, design, engineering, and construction.
Water level monitoring
Water level elevations through April 2023
The DNR Lands and Minerals Division actively monitors the St. James Pit 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. Additionally, state agencies worked collaboratively to gather water quantity and quality information from the St. James, as well as from nearby surface waters that may serve as receiving waters for any constructed outlet.
Water level management undertaken by the city results in downward trends on the water level graph. St. James Pit water level data displayed on the graph include a combination of manual measurements (dashed line) and continuous logger measurements (solid line).
DNR Lands and Minerals Division
St. Paul, MN