MANAGING THE HYDROLOGIC IMPACTS OF MINING ON MINNESOTA'S MESABI IRON RANGE1 by 4 Linda Alderdice2 , John L. Adams 3 , and A. Paul Eger Abstract. Research conducted by the Bureau of Mines, Twin Cities Research Center, and the Minnesota Department of Natural Resources is helping to define the environmental impacts of mining and mineral extraction on the hydrology of Minnesota's Mesabi Iron Range. Cooperative research studies are concentrating on the unique reclamation problems associated with mining on the Range. One study focuses on the impact of open pit mining on surface and groundwater. The ultimate goal of this project is to develop a model which will predict the impacts of these mine pits on the hydrologic balance. This model can be used by mining companies for future mine planning as well as closure operations. The first phase of this project has been to determine the evaporation from open pits as they fill with water at the cessation of mining. The second phase will be to evaluate the groundwater component by assembling and analyzing historical pumping records and pit water levels. Another joint research study is evaluating the use of sulfate reducing bacteria for removing heavy metals from mine waste rock drainage. Four locally available organic materials are being evaluated to determine their effectiveness in removing heavy metals and raising pH. A second phase of this study will determine the most effective organic material for a constructed wetland substrate in field scale experimentation. Additional Keywords: hydrology, Mesabi Iron Range, groundwater, mine pit, hydrologic balance, sulfate reducing bacteria, heavy metals, wetland 1Paper presented at the 9th National Introduction Meeting of the American Society for Surface Mining and Reclamation, Iron mining has long been a Duluth, MN, June 14-18, 1992. major part of Minnesota's history. 2Linda Alderdice is a Soil Natural iron ore was first dis- Scientist, U.S. Bureau of Mines, covered on the Vermilion Range in Twin Cities Research Center, 1850 and on the Mesabi Range in 1866 Minneapolis, MN, 55417. (Minnesota Mining Directory 1989, 3John Adams is a Mining Hydrologist, Figure 1). Ore shipments first left Minnesota Department of Natural the Mesabi Range by rail in 1892, Resources, Division of Waters, from the Mountain Iron Mine. Since Grand Rapids, MN 55744. much of the natural ore was near the 4Paul Eger is a Principal Engineer, surface, open pit mining was exten- Minnesota Department of Natural sively used. Thousands of acres of Resources, Division of Minerals, open pit mines stretch across the St. Paul, MN 55155. Mesabi Range. From 1892 to 1988, the total iron ore shipped from the 108 In the late 1950's, with much of the natural ores nearing exhaustion, ore production was replaced by processing of magnetic taconite materials. Taconite is a metasedi- Toe•••••...... , mentary rock in the Biwabik Iron Formation of Early Proterozoic age ,,,, ....... .. containing hematite and magnetite. ................. It varies in iron content, with about 25 pct magnetic iron present in crude taconite. The Biwabik formation of the Mesabi Range is approximately 100 miles long, 3 miles wide and about 600 feet in thickness (Veith 1988). Taconite mined in Mihnesota in 1989 supplied 70 pct of the Country's usable iron ore (Esparza 1991). The industry provided jobs for over 7500 employees and gener- ,-·-- --~ ated over $940 billion that year in \ economic activity in the form of i "··-'··,.. _,.-~ .. <, payrolls, good and services provid- \!•.. ed, and State and local taxes i Ytrmtllcn .:·~··:".;1....-,_,, ~ugt -~ •• (Esparza 1991). Mtnbl Rlngt Five companies are presently mining taconite at six locations Ouluf' across the Mesabi Range (Figure 1). These operations include National i -·"1 ,...~ Steel, Hibbing Taconite, USX Minntac < ) Plant, Eveleth Mines, Inland Steel '-.l L> Minorca Plant, LTV, and Cyprus ! i Mines. All of these are open pit operations, but the mines are mucl1 jI '"'"Cltt,, ~i I ·-.\. ....._ larger than the open pit natural ore mines of the past. Typical taconite i \,...... mines are several miles long and ~ ,~----·-·-·-·-·-·-·-·-·-·-·-·-------·-iI cover hundreds of acres. Conseq- uently, large quantities of waste material including surface over- burden, waste rock, and tailings are generated from these facilities. Figure 1. - Minnesota's Iron Range The abandoned pits also remain to District fill with water. Post-mining uses exist, such as recreational facilities, aquaculture, and Mesabi Range was over 3.5 billion providing a local water supply if tons (Minnesota Mining Directory proper management is achieved. 1989). The last natural iron ore mine ceased operation in Minnesota Research conducted by the Bureau in 1991. of Mines, Twin Cities Research 109 Center (TCRC), is helping to define significantly altering the hydrology the environmental impacts of mining and water balance in the area. and mineral extraction in Minnesota. Cooperative research studies with Open pits are managed during the Minnesota Department of Natural deactivation of mining operations to Resources (MDNR), Division of achieve long term suitability for a Minerals and Division of Waters, are variety of subsequent uses and may developing models and treatment require pit water monitoring, treat- processes to protect and insure the ment, and/or continued maintenance State's pristine water supplies and after deactivation, to insure resources. This paper is an over- abandoned pits are non-polluting, view of two ongoing studies focusing stable, and free of hazards. on the hydrologic consequences of mining on the Mesabi Iron Range in Groundwater movement, storage, northern Minnesota. and supply are altered during the mining operation. Pumping activi- Open Pit Hydrology Study ties continue through the life of the mine operation, generally In Minnesota, there are two supplying good quality water to agencies that regulate mining. The downstream natural systems, area MDNR regulates mineland planning and residences, and industries. When reclamation, including water use and mining activities cease, pumping hydrologic impact evaluation. The generally stops, and the pits fill Minnesota Pollution Control Agency naturally through surface runoff and (MPCA) regulates water quality and groundwater inflow, and the issues permits based on effluent and hydrology is again altered. receiving stream water standards. These two agencies work jointly to The quantity and quality of insure that the State has a water is often critical to down- continued supply of quality water. stream users and is an important environmental consideration for the To comply with State Reclamation MDNR and MPCA. TCRC and MDNR are Regulations (Dept. of Nat. Res. obtaining data relating to water Rules Relating to Mineland Reclama- storage, the potential for overflow tion, Chapter 6130) and related of the pits, and the ultimate impact statutes (M.S.103G.297), the MDNR on surface and groundwater hydrology must acquire a basic understanding in the area to provide data for of the hydrologic impacts of mining regulators and mining companies in to ultimately develop management planning mining operations and strategies for pre- and post-mine assessing environmental impacts. planning. There is a general lack of Iron ore mining in Minnesota has information available on the hydro- left hundreds of vast open pits on logic consequences of mining on the the earth's surface. Like other Iron Range. Research underway will open pit mines, these pits intercept define and predict the hydrological and store huge quantities of water, changes that occur when the pits are abandoned. The overall objective of 110 this study is to adapt a hydrologic A pit near the extreme eastern model which will include evaporation limit of the Mesabi Iron Range near rates and surface- and groundwater the town of Babbitt, MN, was chosen components so that impacts and for investigation, due to its size, potential utilization of the pits ease of access to the water surface, upon mine closure can be determined. and minimal chance for vandalism (Figure 1). The contract included Phase I: Evaporation Component. provisions for direct measurement of pit evaporation and recording and The morphology of abandoned pits analysis of climatic data for inter- differs from natural lakes in the pretation and extrapolation region. Abandoned pits often have purposes. water depths of over 100 feet and generally exhibit low biological The experiment included the activity. They tend to maximize installation of standard evaporation heat storage due to the clarity of pans, precipitation gauges, anemo- the pit water and the nearly verti- meters, and thermometers. One pan cal pit walls. Large pit areas and weather station were installed intercepting significant amounts of on an upland site adjacent to a water are a primary component of the flooded pit and another was located groundwater flow, and surface water in the flooded, 4-acre pit. The pit evaporation is a major component of evaporation pan was housed in an pit water balance. The large aluminum flotation ring, designed by number and size of pits are believed the Bureau, and partially submerged to significantly affect the in the pit itself. hydrologic balance of the region. Readings were manually recorded The first phase of the study at both sites. Results during the addresses this evaporation component first field season indicated sig- of the water balance. In 1989, a nificant differences in the temp- contract was established between the erature and wind patterns between Bureau and MDNR to measure surface the pit and upland site (Table 1). water evaporation rates of Mesabi Pit water surface evaporation during Iron Range pits. Evaporation over the warmer months of July and August bodies of water has traditionally was greater than anticipated - been a difficult parameter to approximately 70% of that recorded measure due to the small changes in the upland pan. Increased wind over s·hort time periods and effects velocity recorded in the pit of dynamic weather conditions. compared to the upland site sug- Although direct evaporation gested localized air currents were measurements can be used, and data affecting in-pit evaporation.