A River Runs Through It:
Taconite Mining, Sulfate, and the St. Louis River
Michael E. Berndt�Minnesota DNR/ U of M
MMEW Worshop
June 16, 2015
Biwabik Iron Formation
Duluth Complex
St. Louis River
St. Louis River:
>180 miles long
~1100 foot drop from headwaters
to Lake Superior
9283 km2 Drainage Basin
Sulfate Source Plot for St. Louis River
Mining Avg
35 tons/day
Non-Mining Avg
15 tons/day
Mining
Non-Mining
2010
2011
Berndt and Bavin (2012)
2012-2013: Mine Water Research Advisory Panel (MWRAP)
Coordinated studies:
Sediments, water, biology
DOC/Hg/MeHg kinetics
Sulfur cycling, δ34S, δ18O
Topics for today
What lies beneath the landscape?
Where does water go when it rains?
HSPF User’s Manual, v.12.2, 2005
*About 28 inches falls on the landscape annually in this region.
*Little runs off directly to streams, except during bigger storms.
*About 8 inches infiltrates into the groundwater, eventually leaking to streams.
Freshly decaying organic matter is an important reactant.
In a mine, ground water leaks into pit. This and precipitation are pumped out.
Freshly decaying organic matter is not usually an important reactant.
Previously buried materials are exposed to oxygen in air.
Topics for today
What controls the chemistry?�
Water entering the streams takes its chemistry from the riparian soils, … the last soils in contact with the water before it becomes runoff.
(Bishop et al, Hydrol. Proc. 18, 185-189, 2004)
Dissolved Organic Carbon (DOC)
�Former Dissolved Organic Carbon (DOC), separated from water�
Sulfate Reduction
Iron Reduction
Oxidation
Hg2+, MeHg+
Hg2+, Fe2+
Hg2+
Photo-volatilization
Demethylation
Sulfate>1
DOC transports iron and other components, including mercury (Hg), from riparian sediments into the open water.
Berndt et al (in prep)
Event occurred following major rainfall in the non-mining region
St. Louis River
Biwabik Iron Formation
Iron Concentration in the St. Louis River at Scanlon Dam
Iron (Fe)
Fe
Fe
Flow
Flow
Flow
(Event #8)
Iron is released into streams following big storm events.
2010
2011
(Base flow)
A – High Flow
B – Medium Flow
Unsaturated
Saturated
(Base flow)
Berndt et al. (2014)
Different flow rates sample the levels in the soil profile in different proportions.
DOC+ Fe
DOC
DOC+ Fe
Minerals, microbes, and
decaying biota
Minerals, microbes, and
decaying biota
DOC
Fe
Biwabik Iron Formation
St. Louis River Basin
Lake Superior
Topics for today
Photos from Rod Johnson and Associates (2009) Petrography Report for Mesabi Mining
Pyrite in Biwabik Fe Formation
Iron Sulfide as fracture Filling on mine wall
FeS2 alteration products (Melanterite or
Calcite) along bedding plane
Iron oxide coating on pyrite
grain from aged taconite mine waste
Length: 10 um
Scale 50 um
After Wunderly et al. (1996)
Pyrite in mine wastes
FeS2 + 3.75O2 + 3.5 H2O = Fe(OH)3 + 2H2SO4
Pyrite Oxidation:
Sulfuric Acid
Altered Rind
Pyrite
Oxygen
Water
~30 Yr Old Taconite Tails
New Taconite Tails
N/A
N/A
A little pyrite oxidation releases a lot of sulfate!
Bavin et al. (2015)
Carbonate Neutralization:
H2SO4 + 2(Mg,Ca)CO3 = 2(Ca++,Mg++) + SO4= + 2HCO3-
FeS2 + 3.75O2 + 3.5 H2O = Fe(OH)3 + 2H2SO4
Pyrite Oxidation:
Sulfuric Acid
Calcium, Magnesium, Sulfate, and Bicarbonate
Slightly “alkaline” (pH>7)
Carbonate
Minerals
Mg vs SO4 for samples collected in or near mine pits on the Mesabi Iron Range
Topics for today
Jay Cook State Park Swinging Bridge
Thursday, June 21, 2012
Kare 11 News
Pioneer Press
Prior to flood
Skibo
Mile 94
Scanlon
Hydrograph and Sample Dates in 2012
Berndt et al (2014)
Skibo Site Sampling Photos in 2012
Mile 94 Site Sampling Photos in 2012
HSPF = Hydrologic Simulation Program (Fortran)
2014: MPCA commissioned flow model for St. Louis River by Tetratech.
2014-2016: DNR is using the flow model to help quantify mine impacts to chemistry.
(Rutelonis and Berndt – in prep)
Modeled and measured flow at Scanlon Dam
Origin of water in St. Louis River at Scanlon Dam (modeled)
Fraction of water from source
(Rutelonis and Berndt – in prep)
(Rutelonis and Berndt – in prep)
Fraction of water from source
Watershed
Point Sources:
Mining
Non mining
Fraction of water from source
Watershed
Point Sources:
Mining
Non mining
(Rutelonis and Berndt – in prep)
Sulfate vs Magnesium in the St. Louis River in 2012
Upstream site
Downstream Sites
Berndt et al. (2014)
Wet
Drying Out
Downstream
Upstream
Fe vs DOC: Upstream and Downstream from Mining Region
36
36
Berndt et al. (2014)
Wet
Drying out
DNR Website�http://www.dnr.state.mn.us/lands_minerals/dnr_so4_research.html
Acknowledgements