Managing the Hydrologic Impacts of Mining on Minnesota's Mesabi Iron Range1

MANAGING THE HYDROLOGIC IMPACTS OF MINING ON MINNESOTA'S MESABI IRON RANGE1

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. Water intensive methods such as energy temperature profiles were also budget and mass transfer calcula- recorded to describe diurnal and tions are accepted, methods of seasonal patterns and, theref_ore, effectively estimating evaporation predict these influences on from available meterological data is evaporation. limited (Anderson and Jobson 1982). Table 1. - Average Daily Data for the 1989 Partial Season (July 18 through October 31). 1

In-Pit Pan Ueland Pan Month Net Min/Max Total Net Min/Max Total Evaporation(mm) Temp.('C) Wind(krn) Evaporation Temp. ( 'C) Wind(krn)

July 3.69 NA2 NA 5.23 NA NA

August 3.24 18.2/22.8 108 5.0 12.0/24.5 75

September 3.39 13.5/18.0 133 3.44 5.7/17.3 100

October 1. 89 8.0/11.7 110 2.20 0.8/10.5 99

11989 Project Status Report, MDNR 2NA Not Available

Phase II: Groundwater Component. However, manual readings taken several times per week did not Presently, we are expanding our provide the resolution necessary to research to address the groundwater explain evaporation occurrences in component of the water balance the pit, and automatic data record- equation through a comprehensive ing instruments were installed. Two evaluation of another taconite pit electronic monitoring stations now complex, closed since 1985 and record and store average hourly located further west on the Range, evaporation and climatological between Grand Rapids and Hibbing, information such as solar radiation, MN, (Figure 1). This will give us wind speed and direction, pit water an opportunity to evaluate evapora- and pan water temperatures, ambient tive and climatological data in a temperature, and precipitation. The different geologic setting. data collected is being used as input in developing a predictive model Historical pumping records and for estimating pit water evaporation pit water levels will be assembled. at other locations across the Range. Data will be compiled on surface watersheds and flows, pit water Results from the 1990 and 1991 level changes over time, local field seasons are reported by Adams weather conditions, and pit morpho- et al (1992). They indicate that logy, for input into the existing seasonal pan coefficients used to water balance model (the Modified- estimate average annual lake evap- Penrnan-Monteith method) to evaluate oration in Minnesota may be unique the groundwater component of the pit to the flooded pits, and, hence, of complex (Adams et al., 1992). use in mineland impact analyses.

112 Sulfate Reduction for Trace Metal Lake, where elevated levels of metal Removal from Acid Mine Drainage concentrations have been measured in sediments and plant tissues (MDNR Open pit iron mining also 1990, Lapakko and Eger 1981). creates large waste rock stockpiles. These stockpiles range from 80 to In 1989, the cooperative 100 feet high and cover thousands of research agreement with the MDNR acres across the Mesabi Range. In included a task to evaluate biologi- general, the iron formation contains cal remediation methods for removing low levels of trace metals and the metals from acid metal mine drainage drainage from these stockpiles have and to measure the success of not created water quality problems. various, locally available organic However, at the east end of the materials in sustaining sulfate Range, the sulfide-bearing Duluth reduction. The study is also sup- gabbro formation overlies the iron ported by the Bureau of Mines formation. To reach the underlying Pittsburgh Research Center (PRC), taconite ore, the Duluth Complex and adds additional treatment tech- material was stripped off and stock- nologies in their in-house invest- piled. Over 55 million tons of igations of acid mine drainage in Duluth Complex covering over 320 coal mines. acres have been deposited during the last 25 years (Eger et al., 1981). Sulfate reduction has been defined as "a bacterial reaction in Trace metal concentrations of which bacteria use the oxygen copper, nickel, cobalt and zinc have present in the sulfate to oxidize been measured in the natural leach- organic matter to carbon dioxide, ate of gabbro waste rock stockpiles producing sulfide species as a by- at levels 10 to 10,000 times natural product" (Drever 1988). When background levels of local undist- sulfate is reduced to sulfide, urbed streams (Eger et al., 1981). metals present in the drainage react Trace metals may cause adverse to form insoluble metal sulfides. biological impact on aqueous popu- This method has been used success- lations at concentrations less than fully in field-scale tests by PRC 0.010 mg/L (Thingvold et al. 1979, scientists on acid coal mine Lind et al., 1978). Data collected drainage (Dvorak et al., 1991). between 1976 and 1980 showed concentrations of copper and nickel The sulfate reduction field exceeded the 48 hr LC50 for Daphnia study in northern Minnesota began in pulicaria, and nickel exceeded the 1990. Bureau scientists determined 96 hr LC50 for the fathead minnow that sulfate reducing bacteria could (LC50 is a concentration that is grow in the drainage from the Duluth lethal to 50% of the test organisms Complex material (McIntire personal in the indicated amount of communication). Acid drainage col- time)(MDNR 1990). Potential lected from a waste rock stockpile contamination is significantly was subsequently fed through enhanced for surface- and ground reaction barrels containing four waters, wildlife habitats, and locally available organic materials fisheries in nearby Bob Bay of Birch (Eger 1992).

113 Materials included 45-day-old compared to a standard evaporation composted municipal solid waste, coefficient for natural lakes in MN composted yard waste, horse manure of around 78 pct. mixed with sawdust, and composted municipal solid waste followed by Analysis of the evaporation, sawdust. Input and output water meterological, and groundwater chemistry is being determined to components will enhance our ability evaluate the effectiveness and to estimate and predict the effects efficiency of the different organics of the flooded mine pits on the in removing heavy metals and raising Range-wide hydrologic balance. The the pH. primary benefit of this open pit evaporation project will be to Results to date are very promis- provide technological data to ing, with all organic substrates regulators and mining companies to producing an improvement in water aid in pre- and post-mine planning quality (Table 2). The influent, operations to insure that sound which has a pH of 5.1, has been environmental decisions are made. neutralized by all substrates. Concentrations of copper and nickel Leachate flowing from Duluth and levels of sulfate are signifi- gabbro waste rock stockpiles is cantly reduced in all treatments significantly improved by sulfate (Table 2). First year analytical reducing bacteria present in the results and conclusions are reported organic material in the barrel in these proceedings by Eger. reactor study. pH of the influent is neutralized, and concentrations of Additional rows of barrels are copper and nickel are reduced up to now proposed to evaluate a 180-day- 90 pct in all treatments. Sulfate old municipal compost which is more levels are reduced from 860 mg/Lin readily available and may release the influent to around 230 mg/Lin fewer nutrients than the 45-day-old the effluent treated with 45-day-old compost. Drainage from another composted municipal waste. stockpile which has a pH of around 4 and higher levels of trace metals Plans are to continue the will also be treated. sulfate reduction trials to evaluate performance of the organic sub- Summary strates for removing trace metals and increasing pH, to determine the The evaporation component of the effect of residence time on metal hydrologic balance may be unique to removal and to determine the effect the abandoned minepits on the Iron of pH on removal efficiency. Bureau Range compared to natural lakes. and MDNR researchers plan to include Seasonal surface evaporation in open additional field-scale investiga- pits averages around 95 pct of that tions which will utilize the "best" in on-land evaporation stations, organic material in a constructed wetland substrate.

114 1 Table 2. - Water quality, influent, and effluents, 1990 averages . Effluents2 Parameter Influent Row 1 Row 2 Row 3 Row 4 pH 5.1 7.2 7.6 6.9 7.1

Cu (mg/L) 6.4 0.18 0.07 0.07 0.11

Ni (mg/L) 24.4 0.22 0.08 0.10 0.12

Co (mg/L) 1.2 0.06 0.05 0.05 0.05

Zn (mg/L) 1.4 0.26 0.08 0.09 0.17

S04 (mg/L) 860 230 620 660 290

11990 Project Status Report, MDNR 2Row 1 - 45-day old composted municipal waste Row 2 - Composted yard waste Row 3 - Horse manure mixed with wood chips Row 4 - 45-day old composted municipal waste compost followed by wood chips

Literature Cited Drever, J. I. 1988. Geochemistry of Natural Waters. 2nd Ed, Adams, J.L. R.T. Leibfried, G.J. Prentice Hall, Inc. 437 pp. Spoden, L. Alderdice. 1992. Surface Water Evaporation from Eger, A. P., K. A. Lapakko, and A. Mine Pits in Minnesota. In Weir. 1981. The environmental Proc. 9th National Meeting of leaching of stockpiles containing the American Society for Surface copper-nickel sulfide minerals: A Mining and Reclamation, June study of chemical release, 14-18, 1992, Duluth,. MN. chemical transport, and mitigation conducted at Erie Mining Company's Anderson, M.E. and Jobson, H.E. Dunka Mine, Babbitt, MN, 1976- 1982. Comparison of techniques 1980. MDNR, Div. of Minerals, St. for estimating annual lake Paul, MN 62 pp. evaporation using climatological data. Water Resource Res Eger, A. P. 1992. The Use of 18(3):630-636. Sulfate Reduction to Remove Metals from Acid Mine Drainage. Department of Natural Resources. In Proc. 9th Annual Meeting of Rules Relating to Mineland American Society for Surface Reclamation (6MCAR§§l.0401- Mining and Reclamation, June l.0407). 14-18, 1992, Duluth, MN.

115 Esparza, L. E. 1991. Minnesota; Nonferrous Metal Mining: Impact, Minerals Yearbook· 1989, U.S. Mitigation and Prediction Department of the Interior, Research. 1990. MDNR Div. of Bureau of Mines. U.S. Minerals. Non-published Government Printing Office. Internal Report. 1991-281-983/40040. 15 pp. Thingvold, D. A. P. Eger, M. J, Lapakko, K.A. and A. P. Eger. 1981. Hewett, B. Honetschlager, Transport of trace metals and K. Lapakko, R. Mustalish. 1979. other chemical components in Water Resources. In Minnesota mining runoff through a shallow Environmental Quality Board bay. MN Dep. Nat. Res., Div. of Regional Copper-Nickel Study Minerals, St. Paul, MN. 38 pp. 3(4):217 pp.

Minnesota Mining Directory. 1989. Veith, D. L. 1988. Minnesota's Rodney J. Lipp, Ed. Univer. of Unique Mesabi Iron Range. MN Mineral Resources Research Internal BuMines Report. Center, 266 pp. Not published.

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